Clinical Nutrition Book.pdf

A
Dietary Reference Intakes (DRI)
The Dietary Reference Intakes (DRI) include two sets of values that serve as goals for nutrient intake—Recommended Dietary Allowances (RDA) and Adequate
Intakes (AI). The RDA reflect the average daily amount of a nutrient considered adequate to meet the needs of most healthy people. If there is insufficient
evidence to determine an RDA, an AI is set. AI are more tentative than RDA, but both may be used as goals for nutrient intakes. (Chapter 1 provides more details.)
In addition to the values that serve as goals for nutrient intakes (presented in the tables on these two pages), the DRI include a set of values called Tolerable
Upper Intake Levels (UL). The UL represent the maximum amount of a nutrient that appears safe for most healthy people to consume on a regular basis. Turn the
page for a listing of the UL for selected vitamins and minerals.
Estimated Energy Requirements (EER), Recommended Dietary Allowances (RDA), and
Adequate Intakes (AI) for
Water, Energy, and the Energy Nutrients
NOTE: For all nutrients, values for infants are AI. Dashes indicate that values have not been
determined.
aThe water AI includes drinking water, water in beverages, and water in foods; in general,
drinking water and other beverages contribute about 70 to 80 percent, and foods, the remainder.
Conversion factors: 1 L 33.8 fluid oz; 1 L 1.06 qt; 1 cup 8 fluid oz.
bThe Estimated Energy Requirement (EER) represents the average dietary energy intake that will
maintain energy balance in a healthy person of a given gender, age, weight, height, and physical
activity level. The values listed are based on an “active” person at the reference height and weight
and at the midpoint ages for each group until age 19. Chapter 8 and Appendix F provide equa-
tions and tables to determine estimated energy requirements.
cThe linolenic acid referred to in this table and text is the omega-3 fatty acid known as alpha-
linolenic acid.
dThe values listed are based on reference body weights.
eAssumed to be from human milk.
fAssumed to be from human milk and complementary foods and beverages. This includes
approximately 0.6 L (~3 cups) as total fluid including formula, juices, and drinking water.
gFor energy, the age groups for young children are 1–2 years and 3–8 years.
hFor males, subtract 10 kcalories per day for each year of age above 19.
iFor females, subtract 7 kcalories per day for each year of age above 19.
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Age(yr)
Males
0–0.5 — 62 (24) 6 (13) 0.7e 570 60 — 31 4.4 0.5 9.1 1.52
0.5–1 — 71 (28) 9 (20) 0.8f 743 95 — 30 4.6 0.5 11 1.2
1–3g — 86 (34) 12 (27) 1.3 1046 130 19 — 7 0.7 13 1.05
4–8g 15.3 115 (45) 20 (44) 1.7 1742 130 25 — 10 0.9 19 0.95
9–13 17.2 144 (57) 36 (79) 2.4 2279 130 31 — 12 1.2 34 0.95
14–18 20.5 174 (68) 61 (134) 3.3 3152h 130 38 — 16 1.6 52 0.85
19–30 22.5 177 (70) 70 (154) 3.7 3067h 130 38 — 17 1.6 56 0.8
31–50 3.7 3067h 130 38 — 17 1.6 56 0.8
50 3.7 3067h 130 30 — 14 1.6 56 0.8
Females
0–0.5 — 62 (24) 6 (13) 0.7e 520 60 — 31 4.4 0.5 9.1 1.52
0.5–1 — 71 (28) 9 (20) 0.8f 676 95 — 30 4.6 0.5 11 1.2
1–3g — 86 (34) 12 (27) 1.3 992 130 19 — 7 0.7 13 1.05
4–8g 15.3 115 (45) 20 (44) 1.7 1642 130 25 — 10 0.9 19 0.95
9–13 17.4 144 (57) 37 (81) 2.1 2071 130 26 — 10 1.0 34 0.95
14–18 20.4 163 (64) 54 (119) 2.3 2368 130 26 — 11 1.1 46 0.85
19–30 21.5 163 (64) 57 (126) 2.7 2403i 130 25 — 12 1.1 46 0.8
31–50 2.7 2403i 130 25 — 12 1.1 46 0.8
50 2.7 2403i 130 21 — 11 1.1 46 0.8
Pregnancy
1st trimester 3.0 0 175 28 — 13 1.4 25 1.1
2nd trimester 3.0 340 175 28 — 13 1.4 25 1.1
3rd trimester 3.0 452 175 28 — 13 1.4 25 1.1
Lactation
1st 6 months 3.8 330 210 29 — 13 1.3 25 1.3
2nd 6 months 3.8 400 210 29 — 13 1.3 25 1.3
SOURCE: Adapted from the Dietary Reference Intakes series, National Academies Press. Copyright 1997, 1998, 2000, 2001, 2002, 2004, 2005 by the National Academies of Sciences.

B
A
Recommended Dietary Allowances (RDA) and Adequate Intakes (AI) for Vitamins
Recommended Dietary Allowances (RDA) and Adequate Intakes (AI) for Minerals
NOTE: For all nutrients, values for infants are AI. The glossary on the inside back cover defines units
of nutrient measure.
aNiacin recommendations are expressed as niacin equivalents (NE), except for recommendations
for infants younger than 6 months, which are expressed as preformed niacin.
bFolate recommendations are expressed as dietary folate equivalents (DFE).
cVitamin A recommendations are expressed as retinol activity equivalents (RAE).
dVitamin D recommendations are expressed as cholecalciferol and assume an absence of adequate
exposure to sunlight.
eVitamin E recommendations are expressed as -tocopherol.
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Age (yr)
Infants
0–0.5 0.2 0.3 2 5 1.7 0.1 65 0.4 125 40 400 5 4 2.0
0.5–1 0.3 0.4 4 6 1.8 0.3 80 0.5 150 50 500 5 5 2.5
Children
1–3 0.5 0.5 6 8 2 0.5 150 0.9 200 15 300 5 6 30
4–8 0.6 0.6 8 12 3 0.6 200 1.2 250 25 400 5 7 55
Males
9–13 0.9 0.9 12 20 4 1.0 300 1.8 375 45 600 5 11 60
14–18 1.2 1.3 16 25 5 1.3 400 2.4 550 75 900 5 15 75
19–30 1.2 1.3 16 30 5 1.3 400 2.4 550 90 900 5 15 120
31–50 1.2 1.3 16 30 5 1.3 400 2.4 550 90 900 5 15 120
51–70 1.2 1.3 16 30 5 1.7 400 2.4 550 90 900 10 15 120
70 1.2 1.3 16 30 5 1.7 400 2.4 550 90 900 15 15 120
Females
9–13 0.9 0.9 12 20 4 1.0 300 1.8 375 45 600 5 11 60
14–18 1.0 1.0 14 25 5 1.2 400 2.4 400 65 700 5 15 75
19–30 1.1 1.1 14 30 5 1.3 400 2.4 425 75 700 5 15 90
31–50 1.1 1.1 14 30 5 1.3 400 2.4 425 75 700 5 15 90
51–70 1.1 1.1 14 30 5 1.5 400 2.4 425 75 700 10 15 90
70 1.1 1.1 14 30 5 1.5 400 2.4 425 75 700 15 15 90
Pregnancy
≤18 1.4 1.4 18 30 6 1.9 600 2.6 450 80 750 5 15 75
19–30 1.4 1.4 18 30 6 1.9 600 2.6 450 85 770 5 15 90
31–50 1.4 1.4 18 30 6 1.9 600 2.6 450 85 770 5 15 90
Lactation
≤18 1.4 1.6 17 35 7 2.0 500 2.8 550 115 1200 5 19 75
19–30 1.4 1.6 17 35 7 2.0 500 2.8 550 120 1300 5 19 90
31–50 1.4 1.6 17 35 7 2.0 500 2.8 550 120 1300 5 19 90
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Age (yr)
Infants
0–0.5 120 180 400 210 100 30 0.27 2 110 15 200 0.003 0.01 0.2 2
0.5–1 370 570 700 270 275 75 11 3 130 20 220 0.6 0.5 5.5 3
Children
1–3 1000 1500 3000 500 460 80 7 3 90 20 340 1.2 0.7 11 17
4–8 1200 1900 3800 800 500 130 10 5 90 30 440 1.5 1.0 15 22
Males
9–13 1500 2300 4500 1300 1250 240 8 8 120 40 700 1.9 2 25 34
14–18 1500 2300 4700 1300 1250 410 11 11 150 55 890 2.2 3 35 43
19–30 1500 2300 4700 1000 700 400 8 11 150 55 900 2.3 4 35 45
31–50 1500 2300 4700 1000 700 420 8 11 150 55 900 2.3 4 35 45
51–70 1300 2000 4700 1200 700 420 8 11 150 55 900 2.3 4 30 45
70 1200 1800 4700 1200 700 420 8 11 150 55 900 2.3 4 30 45
Females
9–13 1500 2300 4500 1300 1250 240 8 8 120 40 700 1.6 2 21 34
14–18 1500 2300 4700 1300 1250 360 15 9 150 55 890 1.6 3 24 43
19–30 1500 2300 4700 1000 700 310 18 8 150 55 900 1.8 3 25 45
31–50 1500 2300 4700 1000 700 320 18 8 150 55 900 1.8 3 25 45
51–70 1300 2000 4700 1200 700 320 8 8 150 55 900 1.8 3 20 45
70 1200 1800 4700 1200 700 320 8 8 150 55 900 1.8 3 20 45
Pregnancy
≤18 1500 2300 4700 1300 1250 400 27 12 220 60 1000 2.0 3 29 50
19–30 1500 2300 4700 1000 700 350 27 11 220 60 1000 2.0 3 30 50
31–50 1500 2300 4700 1000 700 360 27 11 220 60 1000 2.0 3 30 50
Lactation
≤18 1500 2300 5100 1300 1250 360 10 13 290 70 1300 2.6 3 44 50
19–30 1500 2300 5100 1000 700 310 9 12 290 70 1300 2.6 3 45 50
31–50 1500 2300 5100 1000 700 320 9 12 290 70 1300 2.6 3 45 50

C
Tolerable Upper Intake Levels (UL) for Vitamins
Tolerable Upper Intake Levels (UL) for Minerals
aThe UL for niacin and folate apply to synthetic forms
obtained from supplements, fortified foods, or a combination
of the two.
bThe UL for vitamin A applies to the preformed vitamin only.
cThe UL for vitamin E applies to any form of supplemental
-tocopherol, fortified foods, or a combination of the two.
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c
Age (yr)
Infants
0–0.5 — — — — — 600 25 —
0.5–1 — — — — — 600 25 —
Children
1–3 10 30 300 1000 400 600 50 200
4–8 15 40 400 1000 650 900 50 300
9–13 20 60 600 2000 1200 1700 50 600
Adolescents
14–18 30 80 800 3000 1800 2800 50 800
Adults
19–70 35 100 1000 3500 2000 3000 50 1000
70 35 100 1000 3500 2000 3000 50 1000
Pregnancy
≤18 30 80 800 3000 1800 2800 50 800
19–50 35 100 1000 3500 2000 3000 50 1000
Lactation
≤18 30 80 800 3000 1800 2800 50 800
19–50 35 100 1000 3500 2000 3000 50 1000
dThe UL for magnesium applies to synthetic forms obtained from supplements or drugs only.
eSource of intake should be from human milk (or formula) and food only.
NOTE: An Upper Limit was not established for vitamins and minerals not listed and for those age groups
listed with a dash (—) because of a lack of data, not because these nutrients are safe to consume at any
level of intake. All nutrients can have adverse effects when intakes are excessive.
SOURCE: Adapted with permission from the Dietary Reference Intakes series, National Academies Press.
Copyright 1997, 1998, 2000, 2001, 2002, 2005 by the National Academy of Sciences. Courtesy of the
National Academies Press, Washington, D.C.
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Infants
0–0.5 —e —e — — — 40 4 — 45 — — 0.7 — — — —
0.5–1 —e —e — — — 40 5 — 60 — — 0.9 — — — —
Children
1–3 1500 2300 2500 3000 65 40 7 200 90 1000 2 1.3 300 3 0.2 —
4–8 1900 2900 2500 3000 110 40 12 300 150 3000 3 2.2 600 6 0.3 —
9–13 2200 3400 2500 4000 350 40 23 600 280 5000 6 10 1100 11 0.6 —
Adolescents
14–18 2300 3600 2500 4000 350 45 34 900 400 8000 9 10 1700 17 1.0 —
Adults
19–70 2300 3600 2500 4000 350 45 40 1100 400 10,000 11 10 2000 20 1.0 1.8
70 2300 3600 2500 3000 350 45 40 1100 400 10,000 11 10 2000 20 1.0 1.8
Pregnancy
≤18 2300 3600 2500 3500 350 45 34 900 400 8000 9 10 1700 17 1.0 —
19–50 2300 3600 2500 3500 350 45 40 1100 400 10,000 11 10 2000 20 1.0 —
Lactation
≤18 2300 3600 2500 4000 350 45 34 900 400 8000 9 10 1700 17 1.0 —
19–50 2300 3600 2500 4000 350 45 40 1100 400 10,000 11 10 2000 20 1.0 —

Nutrition
UNDERSTANDING NORMAL AND CLINICAL
SHARON RADY ROLFES | KATHRYN PINNA | ELLIE WHITNEY
Eighth Edition
Australia • Brazil • Japan • Korea • Mexico • Singapore • Spain • United Kingdom • United States

Understanding Normal and Clinical
Nutrition, Eighth Edition
Sharon Rady Rolfes, Kathryn Pinna,
Ellie Whitney
Publisher: Yolanda Cossio
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Printed in Canada
1 2 3 4 5 6 7 12 11 10 09 08

To Ellie Whitney, my mentor,
partner, and friend, with much
appreciation for believing in
me, sharing your wisdom, and
giving me the opportunity to
pursue a career more challenging
and rewarding than any I could
have imagined.
Sharon
To David Stone, for years
of love, friendship, and
assistance with numerous
academic and musical pursuits.
Kathryn
To the memory of
Gary Woodruff, the editor who
first encouraged me to write.
Ellie

About the Authors
Sharon Rady Rolfes received her M.S. in nutrition and food science from
Florida State University. She is a founding member of Nutrition and Health Asso-
ciates, an information resource center that maintains a research database on
over 1000 nutrition-related topics. Her other publications include the college
textbooks Understanding Nutrition and Nutrition for Health and Health Care and a
multimedia CD-ROM called Nutrition Interactive. In addition to writing, she occa-
sionally teaches at Florida State University and serves as a consultant for various
educational projects. Her volunteer work includes coordinating meals for the
hungry and homeless and serving on the steering committee of Working Well, a
community initiative designed to help local businesses improve the health and
well-being of their employees. She maintains her registration as a dietitian and
membership in the American Dietetic Association.
Kathryn Pinna received her M.S. and Ph.D. degrees in nutrition from the
University of California at Berkeley. She has taught nutrition, food science, and
biology courses in the San Francisco Bay Area for over 20 years. She has also
worked as an outpatient dietitian, Internet consultant, and freelance writer. Her
other publications include the textbooks Nutrition for Health and Health Care and
Nutrition and Diet Therapy. She is a registered dietitian and a member of the Amer-
ican Society for Nutrition and the American Dietetic Association.
Ellie Whitney grew up in New York City and received her B.A. and Ph.D.
degrees in English and Biology at Radcliffe/Harvard University and Washington
University, respectively. She has lived in Tallahassee since 1970, has taught at
both Florida State University and Florida AM University, has written newspaper
columns on environmental matters for the Tallahassee Democrat, and has
authored almost a dozen college textbooks on nutrition, health, and related top-
ics, many of which have been revised multiple times over the years. In addition
to teaching and writing, she has spent the past three-plus decades exploring out-
door Florida and studying its ecology. Her latest book is Priceless Florida: The Nat-
ural Ecosystems (Pineapple Press, 2004).

Brief Contents
CHAPTER 1 An Overview of Nutrition 2
H I G H L I G H T Nutrition Information and Misinformation—On the Net and in the News 30
CHAPTER 2 Planning a Healthy Diet 36
H I G H L I G H T Vegetarian Diets 64
CHAPTER 3 Digestion, Absorption, and Transport 70
H I G H L I G H T Common Digestive Problems 92
CHAPTER 4 The Carbohydrates: Sugars, Starches, and Fibers 100
H I G H L I G H T Alternatives to Sugar 132
CHAPTER 5 The Lipids: Triglycerides, Phospholipids, and Sterols 138
H I G H L I G H T High-Fat Foods—Friend or Foe? 172
CHAPTER 6 Protein: Amino Acids 180
H I G H L I G H T Nutritional Genomics 207
CHAPTER 7 Metabolism: Transformations and Interactions 212
H I G H L I G H T Alcohol and Nutrition 238
CHAPTER 8 Energy Balance and Body Composition 248
H I G H L I G H T Eating Disorders 270
CHAPTER 9 Weight Management: Overweight, Obesity, and Underweight 280
H I G H L I G H T The Latest and Greatest Weight-Loss Diet—Again 315
CHAPTER 10 The Water-Soluble Vitamins: B Vitamins and Vitamin C 322
H I G H L I G H T Vitamin and Mineral Supplements 360
CHAPTER 11 The Fat-Soluble Vitamins: A, D, E, and K 368
H I G H L I G H T Antioxidant Nutrients in Disease Prevention 390
CHAPTER 12 Water and the Major Minerals 396
H I G H L I G H T Osteoporosis and Calcium 431
CHAPTER 13 The Trace Minerals 440
H I G H L I G H T Phytochemicals and Functional Foods 469
CHAPTER 14 Life Cycle Nutrition: Pregnancy and Lactation 476
H I G H L I G H T Fetal Alcohol Syndrome 511
CHAPTER 15 Life Cycle Nutrition: Infancy, Childhood, and Adolescence 514
H I G H L I G H T Childhood Obesity and the Early Development of Chronic Diseases 554
CHAPTER 16 Life Cycle Nutrition: Adulthood and the Later Years 560
H I G H L I G H T Hunger and Community Nutrition 583
CHAPTER 17 Nutrition Care and Assessment 588
H I G H L I G H T Nutrition and Immunity 609

vi • BRIEF CONTENTS
CHAPTER 18 Nutrition Intervention 614
H I G H L I G H T Foodborne Illnesses 632
CHAPTER 19 Medications, Herbal Products, and Diet-Drug Interactions 640
H I G H L I G H T Anemia in Illness 657
CHAPTER 20 Enteral Nutrition Support 662
H I G H L I G H T Inborn Errors of Metabolism 682
CHAPTER 21 Parenteral Nutrition Support 686
H I G H L I G H T Ethical Issues in Nutrition Care 704
CHAPTER 22 Metabolic and Respiratory Stress 708
H I G H L I G H T Multiple Organ Dysfunction Syndrome 727
CHAPTER 23 Upper Gastrointestinal Disorders 730
H I G H L I G H T Dental Health and Chronic Illness 750
CHAPTER 24 Lower Gastrointestinal Disorders 754
H I G H L I G H T Probiotics and Intestinal Health 783
CHAPTER 25 Liver Disease and Gallstones 786
H I G H L I G H T Food Allergies 806
CHAPTER 26 Diabetes Mellitus 810
H I G H L I G H T The Metabolic Syndrome 836
CHAPTER 27 Cardiovascular Diseases 840
H I G H L I G H T Feeding Disabilities 868
CHAPTER 28 Renal Diseases 872
H I G H L I G H T Dialysis 896
CHAPTER 29 Cancer and HIV Infection 900
H I G H L I G H T Complementary and Alternative Medicine 921
APPENDIX A Cells, Hormones, and Nerves A-1
APPENDIX B Basic Chemistry Concepts B-1
APPENDIX C Biochemical Structures and Pathways C-1
APPENDIX D Measures of Protein Quality D-1
APPENDIX E Nutrition Assessment: Supplemental Information E-1
APPENDIX F Physical Activity and Energy Requirements F-1
APPENDIX G Exchange Lists for Diabetes G-1
APPENDIX H Table of Food Composition H-1
APPENDIX I WHO: Nutrition Recommendations Canada: Guidelines and Meal Planning I-1
APPENDIX J Healthy People 2010 J-1
APPENDIX K Enteral Formulas K-1

CHAPTER 1
An Overview of Nutrition 2
Food Choices 3
The Nutrients 5
Nutrients in Foods and in the Body 6
The Energy-Yielding Nutrients:
Carbohydrate, Fat, and Protein 7
The Vitamins 10
The Minerals 10
Water 11
The Science of Nutrition 11
Conducting Research 11
Analyzing Research Findings 14
Publishing Research 15
Dietary Reference Intakes 16
Establishing Nutrient Recommendations 16
Establishing Energy Recommendations 18
Using Nutrient Recommendations 18
Comparing Nutrient Recommendations 19
Nutrition Assessment 20
Nutrition Assessment of Individuals 20
Nutrition Assessment of Populations 22
Diet and Health 24
Chronic Diseases 24
Risk Factors for Chronic Diseases 24
H I G H L I G H T 1 Nutrition Information and
Misinformation—On the Net and in the News 30
CHAPTER 2
Planning a Healthy Diet 36
Principles and Guidelines 37
Diet-Planning Principles 37
Dietary Guidelines for Americans 39
Diet-Planning Guides 41
USDA Food Guide 41
Exchange Lists 47
Putting the Plan into Action 48
From Guidelines to Groceries 48
Food Labels 54
The Ingredient List 55
Serving Sizes 55
Nutrition Facts 55
The Daily Values 56
Nutrient Claims 58
Health Claims 59
Structure-Function Claims 59
Consumer Education 60
H I G H L I G H T 2 Vegetarian Diets 64
CHAPTER 3
Digestion, Absorption,
and Transport 70
Digestion 71
Anatomy of the Digestive Tract 72
The Muscular Action of Digestion 74
The Secretions of Digestion 76
The Final Stage 78
Absorption 80
Anatomy of the Absorptive System 80
A Closer Look at the Intestinal Cells 81
The Circulatory Systems 83
The Vascular System 83
The Lymphatic System 84
The Health and Regulation of the GI Tract 86
Gastrointestinal Bacteria 86
Gastrointestinal Hormones and Nerve Pathways 86
The System at Its Best 88
H I G H L I G H T 3 Common Digestive Problems 92
CHAPTER 4
The Carbohydrates: Sugars,
Starches, and Fibers 100
The Chemist’s View of Carbohydrates 101
The Simple Carbohydrates 102
Contents

viii • CONTENTS
Monosaccharides 102
Disaccharides 103
The Complex Carbohydrates 105
Glycogen 105
Starches 105
Fibers 106
Digestion and Absorption of Carbohydrates 107
Carbohydrate Digestion 108
Carbohydrate Absorption 108
Lactose Intolerance 110
Glucose in the Body 111
A Preview of Carbohydrate Metabolism 112
The Constancy of Blood Glucose 113
Health Effects and Recommended Intakes
of Sugars 117
Health Effects of Sugars 117
Controversies Surrounding Sugars 119
Recommended Intakes of Sugars 121
of Starch and Fibers 122
Health Effects of Starch and Fibers 122
Recommended Intakes of Starch and Fibers 124
H I G H L I G H T 4 Alternatives to Sugar 132
CHAPTER 5
The Lipids: Triglycerides,
Phospholipids, and Sterols 138
The Chemist’s View of Fatty Acids and Triglycerides 139
Fatty Acids 140
Triglycerides 142
Degree of Unsaturation Revisited 142
The Chemist’s View of Phospholipids and Sterols 145
Phospholipids 145
Sterols 146
Digestion, Absorption, and Transport of Lipids 147
Lipid Digestion 147
Lipid Absorption 149
Lipid Transport 150
Lipids in the Body 153
Roles of Triglycerides 153
Essential Fatty Acids 154
A Preview of Lipid Metabolism 155
Health Effects and Recommended Intakes of Lipids 156
Health Effects of Lipids 156
Recommended Intakes of Fat 160
H I G H L I G H T 5 High-Fat Foods—Friend or Foe? 172
CHAPTER 6
Protein: Amino Acids 180
The Chemist’s View of Proteins 181
Amino Acids 181
Proteins 183
Digestion and Absorption of Protein 185
Protein Digestion 185
Protein Absorption 185
Proteins in the Body 187
Protein Synthesis 187
Roles of Proteins 189
A Preview of Protein Metabolism 193
Protein in Foods 195
Protein Quality 195
Protein Regulations for Food Labels 196
of Protein 196
Protein-Energy Malnutrition 196
Health Effects of Protein 199
Recommended Intakes of Protein 201
Protein and Amino Acid Supplements 202
H I G H L I G H T 6 Nutritional Genomics 207
CHAPTER 7
Metabolism: Transformations
and Interactions 212
Chemical Reactions in the Body 214
Breaking Down Nutrients for Energy 217
Glucose 219
Glycerol and Fatty Acids 222
Amino Acids 224
Breaking Down Nutrients for Energy—In Summary 226
The Final Steps of Catabolism 227
Energy Balance 230
Feasting—Excess Energy 232
The Transition from Feasting to Fasting 233
Fasting—Inadequate Energy 233
H I G H L I G H T 7 Alcohol and Nutrition 238

CONTENTS • ix
CHAPTER 8
Energy Balance and Body
Composition 248
Energy Balance 249
Energy In: The kCalories Foods Provide 250
Food Composition 250
Food Intake 251
Energy Out: The kCalories the Body Expends 253
Components of Energy Expenditure 254
Estimating Energy Requirements 256
Body Weight, Body Composition, and Health 258
Defining Healthy Body Weight 258
Body Fat and Its Distribution 260
Health Risks Associated with Body Weight
and Body Fat 263
H I G H L I G H T 8 Eating Disorders 270
CHAPTER 9
Weight Management: Overweight,
Obesity, and Underweight 280
Overweight and Obesity 281
Fat Cell Development 282
Fat Cell Metabolism 282
Set-Point Theory 283
Causes of Overweight and Obesity 283
Genetics 284
Environment 286
Problems of Overweight and Obesity 288
Health Risks 288
Perceptions and Prejudices 289
Dangerous Interventions 289
Aggressive Treatments for Obesity 292
Drugs 292
Surgery 292
Weight-Loss Strategies 294
Eating Plans 295
Physical Activity 299
Environmental Influences 302
Behavior and Attitude 303
Weight Maintenance 305
Prevention 306
Public Health Programs 306
Underweight 307
Problems of Underweight 307
Weight-Gain Strategies 307
H I G H L I G H T 9 The Latest and Greatest
Weight-Loss Diet—Again 315
CHAPTER 10
The Water-Soluble Vitamins:
B Vitamins and Vitamin C 322
The Vitamins—An Overview 323
The B Vitamins—As Individuals 326
Thiamin 327
Riboflavin 328
Niacin 331
Biotin 333
Pantothenic Acid 335
Vitamin B6
336
Folate 338
Vitamin B12
342
Non-B Vitamins 345
The B Vitamins—In Concert 346
B Vitamin Roles 347
B Vitamin Deficiencies 348
B Vitamin Toxicities 349
B Vitamin Food Sources 349
Vitamin C 350
Vitamin C Roles 351
Vitamin C Recommendations 352
Vitamin C Deficiency 353
Vitamin C Toxicity 353
Vitamin C Food Sources 354
H I G H L I G H T 1 0 Vitamin and Mineral
Supplements 360
CHAPTER 11
The Fat-Soluble Vitamins:
A, D, E, and K 368
Vitamin A and Beta-Carotene 369
Roles in the Body 370
Vitamin A Deficiency 372
Vitamin A Toxicity 374
Vitamin A Recommendations 374

x • CONTENTS
Vitamin A in Foods 374
Vitamin D 377
Vitamin D Deficiency 378
Vitamin D Toxicity 379
Vitamin D Recommendations and Sources 379
Vitamin E 381
Vitamin E as an Antioxidant 382
Vitamin E Deficiency 382
Vitamin E Toxicity 382
Vitamin E Recommendations 382
Vitamin E in Foods 383
Vitamin K 383
Vitamin K Deficiency 384
Vitamin K Toxicity 385
Vitamin K Recommendations and Sources 385
The Fat-Soluble Vitamins—In Summary 385
H I G H L I G H T 1 1 Antioxidant Nutrients in
Disease Prevention 390
CHAPTER 12
Water and the Major Minerals 396
Water and the Body Fluids 397
Water Balance and Recommended Intakes 398
Blood Volume and Blood Pressure 401
Fluid and Electrolyte Balance 402
Fluid and Electrolyte Imbalance 406
Acid-Base Balance 406
The Minerals—An Overview 408
Sodium 410
Chloride 413
Potassium 414
Calcium 416
Calcium Roles in the Body 416
Calcium Recommendations and Sources 418
Calcium Deficiency 421
Phosphorus 422
Magnesium 423
Sulfate 425
H I G H L I G H T 1 2 Osteoporosis and Calcium 431
CHAPTER 13
The Trace Minerals 440
The Trace Minerals—An Overview 441
Iron 442
Iron Roles in the Body 442
Iron Absorption and Metabolism 443
Iron Deficiency 445
Iron Toxicity 447
Iron Recommendations and Sources 449
Iron Contamination and Supplementation 450
Zinc 452
Zinc Roles in the Body 452
Zinc Absorption and Metabolism 452
Zinc Deficiency 453
Zinc Toxicity 454
Zinc Recommendations and Sources 454
Zinc Supplementation 455
Iodine 455
Selenium 457
Copper 458
Manganese 459
Fluoride 460
Chromium 461
Molybdenum 462
Other Trace Minerals 462
Contaminant Minerals 463
Closing Thoughts on the Nutrients 463
H I G H L I G H T 1 3 Phytochemicals and
Functional Foods 469
CHAPTER 14
Life Cycle Nutrition: Pregnancy
and Lactation 476
Nutrition prior to Pregnancy 477
Growth and Development during Pregnancy 478
Placental Development 478
Fetal Growth and Development 478
Critical Periods 480

CONTENTS • xi
Maternal Weight 483
Weight prior to Conception 484
Weight Gain during Pregnancy 484
Exercise during Pregnancy 486
Nutrition during Pregnancy 487
Energy and Nutrient Needs during Pregnancy 488
Vegetarian Diets during Pregnancy and Lactation 492
Common Nutrition-Related Concerns of Pregnancy 492
High-Risk Pregnancies 493
The Infant’s Birthweight 493
Malnutrition and Pregnancy 494
Food Assistance Programs 495
Maternal Health 495
The Mother’s Age 497
Practices Incompatible with Pregnancy 498
Nutrition during Lactation 500
Lactation: A Physiological Process 501
Breastfeeding: A Learned Behavior 502
Maternal Energy and Nutrient Needs during Lactation 502
Maternal Health 504
Practices Incompatible with Lactation 505
H I G H L I G H T 1 4 Fetal Alcohol Syndrome 511
CHAPTER 15
Life Cycle Nutrition: Infancy,
Childhood, and Adolescence 514
Nutrition during Infancy 515
Energy and Nutrient Needs 515
Breast Milk 518
Infant Formula 520
Special Needs of Preterm Infants 522
Introducing Cow’s Milk 522
Introducing Solid Foods 523
Mealtimes with Toddlers 525
Nutrition during Childhood 526
Hunger and Malnutrition in Children 530
The Malnutrition-Lead Connection 532
Hyperactivity and “Hyper” Behavior 532
Food Allergy and Intolerance 533
Childhood Obesity 535
Mealtimes at Home 539
Nutrition at School 541
Nutrition during Adolescence 543
Growth and Development 543
Food Choices and Health Habits 545
Problems Adolescents Face 546
H I G H L I G H T 1 5 Childhood Obesity and the Early
Development of Chronic Diseases 554
CHAPTER 16
Life Cycle Nutrition: Adulthood
and the Later Years 560
Nutrition and Longevity 562
Observation of Older Adults 563
Manipulation of Diet 564
The Aging Process 565
Physiological Changes 566
Other Changes 568
Energy and Nutrient Needs of Older Adults 569
Water 569
Energy and Energy Nutrients 569
Vitamins and Minerals 570
Nutrient Supplements 571
Nutrition-Related Concerns of Older Adults 572
Vision 572
Arthritis 573
The Aging Brain 574
Food Choices and Eating Habits
of Older Adults 575
Food Assistance Programs 576
Meals for Singles 577
H I G H L I G H T 1 6 Hunger and Community
Nutrition 583
CHAPTER 17
Nutrition Care and Assessment 588
Nutrition in Health Care 589
Effects of Illness on Nutrition Status 589
Responsibility for Nutrition Care 590
Nutrition Screening 591
The Nutrition Care Process 593
Nutrition Assessment 595
Historical Information 595
Food Intake Data 596
Anthropometric Data 599
Biochemical Data 601
Medical Tests and Procedures 604
Physical Examinations 604
H I G H L I G H T 1 7 Nutrition and Immunity 609

xii • CONTENTS
CHAPTER 18
Nutrition Intervention 614
Implementing Nutrition Care 615
Documenting Nutrition Care 615
Approaches to Nutrition Care 617
Determining Energy Requirements 619
Dietary Modifications 621
Modified Diets 621
Alternative Feeding Routes 624
Nothing by Mouth (NPO) 625
Foodservice 626
Menu Planning 626
Food Selection 626
Food Preparation and Delivery 627
Food Safety 628
Improving Food Intake 628
H I G H L I G H T 1 8 Foodborne Illnesses 632
CHAPTER 19
Medications, Herbal Products,
and Diet-Drug Interactions 640
Medications in Disease Treatment 641
Risks from Medications 642
Patients at High Risk of Adverse Effects 643
Herbal Products 644
Effectiveness and Safety of Herbal Products 644
Use of Herbal Products in Illness 646
Diet-Drug Interactions 648
Drug Effects on Food Intake 648
Drug Effects on Nutrient Absorption 648
Dietary Effects on Drug Absorption 650
Drug Effects on Nutrient Metabolism 650
Dietary Effects on Drug Metabolism 651
Drug Effects on Nutrient Excretion 651
Dietary Effects on Drug Excretion 652
Diet-Drug Interactions and Toxicity 652
H I G H L I G H T 1 9 Anemia in Illness 657
CHAPTER 20
Enteral Nutrition Support 662
Enteral Formulas 663
Types of Enteral Formulas 664
Formula Characteristics 665
Enteral Nutrition in Medical Care 666
Oral Use of Enteral Formulas 666
Indications for Tube Feedings 666
Feeding Routes 667
Formula Selection 669
Meeting Water Needs 671
Administration of Tube Feedings 671
Safe Handling 671
Initiating and Progressing a Tube Feeding 672
Medication Delivery through Feeding Tubes 675
Tube Feeding Complications 675
Transition to Table Foods 676
H I G H L I G H T 2 0 Inborn Errors of Metabolism 682
CHAPTER 21
Parenteral Nutrition Support 686
Indications for Parenteral Nutrition 687
Parenteral Solutions 690
Parenteral Nutrients 690
Solution Preparation 691
Administering Parenteral Nutrition 694
Insertion and Care of Intravenous Catheters 694
Administration of Parenteral Solutions 696
Discontinuing Intravenous Feedings 696
Managing Metabolic Complications 697
Nutrition Support at Home 698
Candidates for Home Nutrition Support 698
Planning Home Nutrition Care 699
Quality-of-Life Issues 700
H I G H L I G H T 2 1 Ethical Issues in Nutrition Care 704

CONTENTS • xiii
CHAPTER 22
Metabolic and Respiratory
Stress 708
The Body’s Responses to Stress and Injury 709
Hormonal Responses to Stress 710
The Inflammatory Response 710
Nutrition Treatment of Acute Stress 712
Determining Nutritional Requirements 712
Approaches to Nutrition Care in Acute Stress 715
Patients with Burn Injuries 715
Nutrition and Respiratory Stress 717
Chronic Obstructive Pulmonary Disease 717
Respiratory Failure 721
H I G H L I G H T 2 2 Multiple Organ Dysfunction
Syndrome 727
CHAPTER 23
Upper Gastrointestinal
Disorders 730
Conditions Affecting the Esophagus 731
Dysphagia 731
Gastroesophageal Reflux Disease 734
Conditions Affecting the Stomach 738
Dyspepsia 738
Nausea and Vomiting 739
Gastritis 739
Peptic Ulcer Disease 740
Gastric Surgery 741
Gastrectomy 742
Bariatric Surgery 745
H I G H L I G H T 2 3 Dental Health and Chronic
Illness 750
CHAPTER 24
Lower Gastrointestinal Disorders 754
Common Intestinal Problems 755
Constipation 755
Intestinal Gas 758
Diarrhea 758
Malabsorption Syndromes 760
Fat Malabsorption 760
Bacterial Overgrowth 761
Conditions Affecting the Pancreas 763
Pancreatitis 764
Cystic Fibrosis 765
Conditions Affecting the Small Intestine 767
Celiac Disease 767
Inflammatory Bowel Diseases 768
Short Bowel Syndrome 771
Conditions Affecting the Large Intestine 774
Irritable Bowel Syndrome 774
Diverticular Disease of the Colon 776
Colostomies and Ileostomies 777
H I G H L I G H T 2 4 Probiotics and Intestinal
Health 783
CHAPTER 25
Liver Disease and Gallstones 786
Fatty Liver and Hepatitis 787
Fatty Liver 788
Hepatitis 789
Cirrhosis 790
Consequences of Cirrhosis 791
Treatment of Cirrhosis 793
Medical Nutrition Therapy for Cirrhosis 794
Liver Transplantation 797
Gallbladder Disease 798
Types of Gallstones 798
Consequences of Gallstones 799
Risk Factors for Gallstones 800
Treatment for Gallstones 800
H I G H L I G H T 2 5 Food Allergies 806
CHAPTER 26
Diabetes Mellitus 810
Overview of Diabetes Mellitus 811
Symptoms of Diabetes Mellitus 812
Diagnosis of Diabetes Mellitus 812
Types of Diabetes Mellitus 813
Prevention of Type 2 Diabetes Mellitus 815
Acute Complications of Diabetes Mellitus 815
Chronic Complications of Diabetes Mellitus 817

xiv • CONTENTS
Treatment of Diabetes Mellitus 818
Treatment Goals 818
Evaluating Diabetes Treatment 819
Body Weight Concerns 820
Medical Nutrition Therapy: Nutrient
Recommendations 821
Medical Nutrition Therapy: Meal-Planning
Strategies 822
Insulin Therapy 823
Antidiabetic Drugs 828
Physical Activity and Diabetes Management 828
Sick-Day Management 830
Diabetes Management in Pregnancy 830
Pregnancy in Type 1 or Type 2 Diabetes 831
Gestational Diabetes 831
H I G H L I G H T 2 6 The Metabolic Syndrome 836
CHAPTER 27
Cardiovascular Diseases 840
Atherosclerosis 841
Consequences of Atherosclerosis 842
Development of Atherosclerosis 842
Causes of Atherosclerosis 843
Coronary Heart Disease (CHD) 845
Symptoms of Coronary Heart Disease 845
Evaluating Risk for Coronary Heart Disease 845
Therapeutic Lifestyle Changes for Lowering
CHD Risk 847
Lifestyle Changes for Hypertriglyceridemia 852
Vitamin Supplementation and CHD Risk 854
Drug Therapies for CHD Prevention 854
Treatment of Heart Attack 855
Hypertension 856
Factors That Influence Blood Pressure 856
Factors That Contribute to Hypertension 857
Treatment of Hypertension 858
Heart Failure 861
Consequences of Heart Failure 861
Medical Management of Heart Failure 862
Stroke 863
Stroke Prevention 863
Stroke Management 864
H I G H L I G H T 2 7 Feeding Disabilities 868
CHAPTER 28
Renal Diseases 872
Functions of the Kidneys 873
The Nephrotic Syndrome 874
Consequences of the Nephrotic Syndrome 875
Treatment of the Nephrotic Syndrome 875
Acute Renal Failure 878
Causes of Acute Renal Failure 878
Consequences of Acute Renal Failure 878
Treatment of Acute Renal Failure 879
Chronic Kidney Disease 880
Consequences of Chronic Kidney Disease 881
Treatment of Chronic Kidney Disease 882
Kidney Transplants 886
Kidney Stones 888
Formation of Kidney Stones 889
Consequences of Kidney Stones 889
Prevention and Treatment of Kidney Stones 891
H I G H L I G H T 2 8 Dialysis 896
CHAPTER 29
Cancer and HIV Infection 900
Cancer 901
How Cancer Develops 901
Nutrition and Cancer Risk 903
Consequences of Cancer 905
Treatments for Cancer 906
Medical Nutrition Therapy for Cancer 907
HIV Infection 911
Consequences of HIV Infection 911
Treatments for HIV Infection 913
Medical Nutrition Therapy for HIV Infection 915
H I G H L I G H T 2 9 Complementary and Alternative
Medicine 921

CONTENTS • xv
APPENDIX A Cells, Hormones, and Nerves A-1
APPENDIX B Basic Chemistry Concepts B-1
APPENDIX C Biochemical Structures
and Pathways C-1
APPENDIX D Measures of Protein Quality D-1
APPENDIX E Nutrition Assessment: Supplemental
Information E-1
APPENDIX F Physical Activity and Energy
Requirements F-1
APPENDIX G Exchange Lists for Diabetes G-1
APPENDIX H Table of Food Composition H-1
APPENDIX I WHO: Nutrition Recommendations
Canada: Guidelines and Meal
Planning I-1
APPENDIX J Healthy People 2010 J-1
APPENDIX K Enteral Formulas K-1
Glossary GL-1
Index IN-1
Aids To Calculation W
Dietary Reference Intakes
(Inside Front Covers)
Daily Values For Food Labels
(Inside Back Cover, Left)
Body Mass Index (BMI)
(Inside Back Cover, Right)

xvi • CONTENTS
HOW TO BOXES
Chapter 1
Think Metric 8
Calculate the Energy Available from Foods 9
Determine Whether a Website Is Reliable 31
Find Credible Sources of Nutrition Information 33
Chapter 2
Compare Foods Based on Nutrient Density 38
Calculate Personal Daily Values 57
Chapter 5
Make Heart-Healthy Choices—by Food Group 163
Calculate a Personal Daily Value for Fat 165
Understand “% Daily Value” and “% kCalories from Fat” 167
Chapter 6
Calculate Recommended Protein Intake 201
Chapter 8
Estimate Energy Requirements 257
Determine Body Weight Based on BMI 261
Chapter 9
Compare Foods Based on Energy Density 297
Chapter 10
Understand Dose Levels and Effects 325
Evaluate Foods for Their Nutrient Contributions 329
Estimate Niacin Equivalents 333
Estimate Dietary Folate Equivalents 339
Distinguish Symptoms and Causes 350
Chapter 12
Cut Salt (and Sodium) Intake 411
Estimate Your Calcium Intake 420
Chapter 13
Estimate the Recommended Daily Intake for Iron 449
Chapter 15
Plot Measures on a Growth Chart 516
Protect against Lead Toxicity 533
Chapter 16
Estimate Energy Requirements for Older Adults 570
Identify Food Insecurity in a U.S. Household 584
Plan Healthy, Thrifty Meals 585
Chapter 17
Measure Length and Height 600
Measure Weight 600
Estimate and Evaluate %IBW and %UBW 602
Chapter 18
Estimate the Energy Requirements of a Hospital Patient 621
Help Hospital Patients Improve Their Food Intakes 629
Prevent Foodborne Illnesses 636
Chapter 19
Reduce the Risks of Adverse Effects from Medications 644
Prevent Diet-Drug Interactions 653
Chapter 20
Help Patients Accept Oral Formulas 666
Help Patients Cope with Tube Feedings 673
Determine the Formula Volumes to Administer
in Tube Feedings 674
Administer Medications to Patients Receiving
Tube Feedings 675
Chapter 21
Express the Osmolar Concentration of a Solution 689
Calculate the Macronutrient and Energy Content
of a Parenteral Solution 692
Calculate the Nonprotein kCalorie-to-Nitrogen Ratio 693
Chapter 22
Estimate the Energy Needs of a Critical Care Patient 714
Chapter 23
Improve Acceptance of Mechanically Altered Foods 735
Manage Gastrointestinal Reflux Disease 737
Alter the Diet to Reduce Symptoms of Dumping
Syndrome 744
Alter Dietary Habits to Achieve and Maintain Weight Loss
after Bariatric Surgery 746
Chapter 24
Follow a Fat-Restricted Diet 763
Chapter 25
Help the Person with Cirrhosis Eat Enough Food 795
Chapter 26
Use Carbohydrate Counting in Clinical Practice 824
Chapter 27
Assess a Person’s Risk of Heart Disease 847
Detect, Evaluate, and Treat High Blood Cholesterol 848
Implement a Heart-Healthy Diet 853
Reduce Sodium Intake 860
Chapter 28
Help Patients Comply with a Renal Diet 886
Chapter 29
Increase kCalories and Protein in Meals 908
Help Patients Handle Food-Related Problems 910

CONTENTS • xvii
CASE STUDIES
Chapter 17
Nutrition Screening and Assessment 605
Chapter 18
Implementing Nutrition Care 629
Chapter 20
Graphics Designer Requiring Enteral Nutrition Support 678
Chapter 21
Geologist Requiring Parenteral Nutrition 699
Chapter 22
Mortgage Broker with a Severe Burn 717
Elderly Person with Emphysema 721
Chapter 23
Accountant with GERD 737
Biology Teacher Requiring Gastric Surgery 745
Chapter 24
Retired Executive with Chronic Pancreatitis 765
Child with Cystic Fibrosis 766
Economist with Short Bowel Syndrome 773
New College Graduate with Irritable Bowel Syndrome 775
Chapter 25
Carpenter with Cirrhosis 796
Chapter 26
Child with Type 1 Diabetes 831
School Counselor with Type 2 Diabetes 832
Chapter 27
Computer Programmer with Cardiovascular Disease 861
Chapter 28
Store Manager with Acute Renal Failure 881
Banker with Chronic Kidney Disease 887
Chapter 29
Public Relations Consultant with Cancer 911
Financial Planner with HIV Infection 916

Preface
Each year brings new discoveries in nutrition science. Staying current in this remark-
able field remains a challenge for educators and health professionals alike. In this
eighth edition of Understanding Normal and Clinical Nutrition, we present updated,
comprehensive coverage of the fundamentals of nutrition and nutrition therapy for
an introductory nutrition course. The early chapters focus on “normal” nutrition—
recommendations about nutrition that are essential for maintaining health and
preventing disease. The later chapters provide lessons in “clinical” nutrition—the
pathophysiology and nutrition therapy for a wide range of medical conditions. As
with previous editions, each chapter has been substantially revised and updated.
New research topics, such as functional foods, probiotics, cytokines, and nutritional
genomics, are introduced or more fully explored. The chapters include practical in-
formation and valuable resources to help readers apply nutrition knowledge and
skills to their daily lives and the clinical setting.
Our goal in writing this book has always been to share our excitement about the
field of nutrition in a manner that motivates students to study and learn. Moreover,
we seek to provide accurate, current information that is meaningful to the student
or health professional. Individuals who study nutrition often find nutritional sci-
ence to be at once both fascinating and overwhelming; there are so many “details”
to learn—new terms, new chemical structures, and new biological concepts. Taken
one step at a time, however, the science of nutrition may seem less daunting and
the “facts” more memorable. We hope that this book serves you well.
The Chapters Chapter 1 begins by exploring why we eat the foods we do and con-
tinues with a brief overview of the nutrients, the science of nutrition, recommended
nutrient intakes, assessment, and important relationships between diet and health.
Chapter 2 describes the diet-planning principles and food guides used to create diets
that support good health and includes instructions on how to read a food label. In
Chapter 3, readers follow the journey of digestion and absorption as the body trans-
forms foods into nutrients. Chapters 4 through 6 describe carbohydrates, fats, and
proteins—their chemistry, roles in the body, and places in the diet. Chapter 7 shows
how the body derives energy from these three nutrients. Chapters 8 and 9 continue the
story with a look at energy balance, the factors associated with overweight and under-
weight, and the benefits and dangers of weight loss and weight gain. Chapters 10
through 13 describe the vitamins, the minerals, and water—their roles in the body, de-
ficiency and toxicity symptoms, and food sources. Chapters 14 through 16 complete
the “normal” chapters by presenting the special nutrient needs of people who are at
different phases of the life cycle—pregnancy and lactation, infancy, childhood, ado-
lescence, and adulthood and the later years.
The remaining “clinical” chapters of the book focus on the nutrition care of in-
dividuals with health problems. Chapter 17 explains how illnesses and their treat-
ments influence nutrient needs and describes the process of nutrition assessment.
Chapter 18 discusses how nutrition care is implemented and introduces the differ-
ent types of therapeutic diets used in patient care. Chapter 19 explores the poten-
tial interactions between nutrients and medications and examines the benefits and
risks associated with herbal remedies. Chapters 20 and 21 describe special ways of
feeding people who cannot eat conventional foods. Chapter 22 explains the in-
flammatory process and shows how metabolic and respiratory stress influence nu-

PREFACE • xix
trient needs. Chapters 23 through 29 explore the pathology, medical treatment,
and nutrition care associated with specific diseases, including gastrointestinal dis-
orders, liver disease, diabetes mellitus, cardiovascular diseases, renal diseases, can-
cer, and HIV infection.
The Highlights Every chapter is followed by a highlight that provides readers with
an in-depth look at a current, and often controversial, topic that relates to its compan-
ion chapter. New highlights in this edition feature foodborne illnesses and the role of
probiotics in intestinal health.
Special Features The art and layout in this edition have been carefully designed to
be inviting while enhancing student learning. In addition, special features help read-
ers identify key concepts and apply nutrition knowledge. For example, when a new
term is introduced, it is printed in bold type and a definition is provided. These defi-
nitions often include pronunciations and derivations to facilitate understanding. A
glossary at the end of the book includes all defined terms.
These guidelines provide science-based advice to promote health and to
reduce the risk of chronic disease through diet and physical activity.
Each major section within a chapter concludes with a summary paragraph
that reviews the key concepts. Similarly, summary tables organize informa-
tion in an easy-to-read format.
Chapters 1 through 16 begin with Nutrition in Your Life sections that introduce the essece of the chapter with a friendly
and familiar scenario. Similiarly, Chapters 17 through 29 begin with Nutrition in the Clinical Setting sections, which in-
troduce real-life concerns associated with diseases or their treatments.
IN SUMMARY
Also featured in this edition are the Dietary Guidelines for Americans 2005 recom-
mendations, which are introduced in Chapter 2 and presented throughout the text
whenever their subjects are discussed. Look for the following design.
definition (DEF-eh-NISH-en): the meaning of
a word.
• de = from
• finis = boundary
At the end of Chapters 1 through 16, a Nutrition Portfolio section revisits the messages
introduced in the chapter and prompts readers to consider whether their personal
choices meet the dietary goals discussed. Chapters 17 through 29 end with a Clinical
Portfolio section, which enables readers to practice their clinical skills by addressing hypo-
thetical clinical situations.
Nutrition Portfolio/Clinical Portfolio
Nutrition in Your Life/Nutrition in the Clinical Setting

xx • PREFACE
Several of the early chapters close with a “Nutrition Calcula-
tion” section. These sections often reinforce the “How to” les-
sons and provide practice in doing nutrition-related
calculations. The problems enable readers to practice their
skills and then check their answers (found at the end of the
chapter). Readers who successfully master these exercises will
be well prepared for “real-life” nutrition-related problems.
NUTRITION CALCULATIONS
Each chapter and many highlights conclude with Nutrition on
the Net—a list of websites for further study of topics covered in
the accompanying text. These lists do not imply an endorse-
ment of the organizations or their programs. We have tried to
provide reputable sources, but cannot be responsible for the
content of these sites. (Read Highlight 1 to learn how to find re-
liable information on the Internet.)
NUTRITION ON THE NET
Each chapter ends with study questions in essay and multiple-
choice format. Study questions offer readers the opportunity to
review the major concepts presented in the chapters in prepa-
ration for exams. The page numbers after each essay question
refer readers to discussions that answer the question; multiple-
choice answers appear at the end of the chapter.
STUDY QUESTIONS
The clinical chapters include case studies that present problems and pose questions that al-
low readers to apply chapter material to hypothetical situations. Readers who successfully
master these exercises will be better prepared to face “real-life” challenges that arise in the
clinical setting.
CASE STUDY
The clinical chapters close with a Nutrition Assess-
ment Checklist that helps readers evaluate how
various disorders impair nutrition status. These
sections highlight the medical, dietary, anthropo-
metric, biochemical, and physical findings most
relevant to patients with specific diseases.
NUTRITION ASSESSMENT CHECKLIST
Most of the clinical chapters also include a section on Diet-Drug Interactions that
describes the nutrition-related concerns associated with the medications commonly
used to treat the disorders described in the chapter.
Many of the chapters include “How to” sec-
tions that guide readers through problem-
solving tasks. For example, the “How to” in
Chapter 1 takes students through the steps of
calculating energy intake from the grams of
carbohydrate, fat, and protein in a food;
another “How to” in Chapter 18 shows how
to estimate the energy requirements of a hos-
pital patient.
HOW TO

PREFACE • xxi
The Appendixes The appendixes are valuable references for a number of purposes.
Appendix A summarizes background information on the hormonal and nervous sys-
tems, complementing Appendixes B and C on basic chemistry, the chemical structures
of nutrients, and major metabolic pathways. Appendix D describes measures of pro-
tein quality. Appendix E provides supplemental coverage of nutrition assessment. Ap-
pendix F presents the estimated energy requirements for men and women at various
levels of physical activity. Appendix G presents the 2007 U.S. Exchange System. Ap-
pendix H is an 8000-item food composition table compiled from the latest nutrient
database assembled by Axxya Systems. Appendix I presents recommendations from
the World Health Organization (WHO) and information for Canadians—the 2005 Be-
yond the Basics meal-planning system and 2007 guidelines for healthy eating and
physical activities. Appendix J presents the Healthy People 2010 nutrition-related ob-
jectives. Appendix K provides examples of commercial enteral formulas commonly
used in tube feedings or to supplement oral diets.
The Inside Covers The inside covers put commonly used information at your
fingertips. The front covers (pp. A, B, and C) present the current nutrient recom-
mendations; the inside back cover (p. Y on the left) features the Daily Values used
on food labels and a glossary of nutrient measures; and the inside back cover (p.
Z on the right) shows suggested weight ranges for various heights (based on the
Body Mass Index). The pages just prior to the back cover (pp. W–X) assist readers
with calculations and conversions.
Closing Comments We have taken great care to provide accurate information and
have included many references at the end of each chapter and highlight. To keep the
number of references manageable, however, many statements that appeared in pre-
vious editions with references now appear without them. All statements reflect current
nutrition knowledge, and the authors will supply references to back editions upon re-
quest. In addition to supporting text statements, the end-of-chapter references provide
readers with resources for finding a good overview or more details on the subject. Nu-
trition is a fascinating subject, and we hope our enthusiasm for it comes through on
every page.
Sharon Rady Rolfes
Kathryn Pinna
Ellie Whitney
May 2008

xxii • PREFACE
Acknowledgments
To produce a book requires the coordinated effort of a team of people—and, no
doubt, each team member has another team of support people as well. We salute,
with a big round of applause, everyone who has worked so diligently to ensure the
quality of this book.
We thank our partners and friends, Linda DeBruyne and Fran Webb, for their
valuable consultations and contributions; working together over the past 20+ years
has been a most wonderful experience. We especially appreciate Linda’s research
assistance on several chapters. Special thanks go to our colleagues Gail Hammond
for her Canadian perspective, Sylvia Crews for her revision of the Aids to Calcula-
tion section at the end of the book, and David Stone for his careful critique of sev-
eral newly written sections in the clinical chapters. A thousand thank-yous to Beth
Magana, Marni Jay Rolfes, and Alex Rodriguez for their careful attention to man-
uscript preparation and a multitude of other daily tasks.
We also thank the many people who have prepared the ancillaries that accom-
pany this text: Harry Sitren and Ileana Trautwein for writing and enhancing the
test bank; Gail Hammond, Melissa Langone, Barbara Quinn, Tania Rivera, Sharon
Stewart, Lori Turner, and Daryle Wane for contributing to the instructor’s manual;
Connie Goff for preparing PowerPoint lecture presentations; and Celine Heskey for
creating materials for Cengage Now. Thanks also to the folks at Axxya for their as-
sistance in creating the food composition appendix and developing the computer-
ized diet analysis program that accompanies this book.
Our special thanks to our editorial team for their hard work and enthusiasm—
Peter Adams for his leadership and support; Anna Lustig for her efficient analysis
of reviews and patience during manuscript preparation; Trudy Brown for her efforts
in managing production; Mary Berry for her outstanding copyediting abilities, in-
terest in accuracy, and eye for detail; Gary Kliewer of The Book Company for his
diligent attention to the innumerable details involved in production; Roman
Barnes for the extra care he took to locate meaningful photos; Pat Lewis for proof-
reading the final text pages; Elesha Feldman for her competent coordination of an-
cillaries and her work on the food composition appendix; and Erin Taylor for
composing a thorough and useful index. We’d also like to thank Diane Beasley for
creatively designing these pages, Cathy Leonard for coordinating artwork and
page production, and Karyn Morrison and Margaret Chamberlain-Gaston for their
assistance in obtaining permissions. To the many, many others involved in produc-
tion and sales, we tip our hats in appreciation.
We are especially grateful to our associates, friends, and families for their con-
tinued encouragement and support. We also thank our many reviewers for their
comments and contributions to this edition and all previous editions.

PREFACE • xxiii
Melody Anacker
Montana State University
Janet Anderson
Utah State University
Judi Brooks
Eastern Michigan University
Richard S. Crow
University of Minnesota
Robert Davidson
Brigham Young University
Marguerite Dunne
Marist College
Brenda Eissenstat
Pennsylvania State
University
Cindy Fitch
West Virginia University
Mary Flynn
Brown University
Gloria Gonzalez
Pensacola Junior College
Kathleen Gould
Townson University
Kathryn Henry
Hood College
Le Greta Hudson
University of
Missouri–Columbia
Dale Larson
Johnson Community College
Katy Lenker
University of Central
Oklahoma
Lorraine Lewis
Viterbo University
Kimberly Lower
Collin County Community
College
Mary Maciolek
Middlesex County College
Kim McMahon
Utah State University
Steven Nizielski
Grand Valley State
University
Anna Page
Johnson County
Community College
Sarah Panarello
Yakima Valley Community
College
Roman Pawlak
East Carolina University
Sue Roberts
Walla Walla Community College
Linda Shepherd
College of Saint Benedict, Saint
John’s University
Sandra Shortt
Cedarville University
Denise Signorelli
Community College
of Southern Nevada
Mollie Smith
California State University,
Fresno
Luann Soliah
Baylor University
Tammy Stephenson
University of Kentucky
Sherry Stewart
University of Texas at Dallas
Trinh Tran
City College of San Francisco
Eric Vlahov
University of Tampa
Janelle Walter
Baylor University
Stacie Wing-Gaia
University of Utah
Reviewers of Understanding Normal and Clinical Nutrition

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Believe it or not, you have probably eaten at least 20,000 meals in your life.
Without any conscious effort on your part, your body uses the nutrients from
those foods to make all its components, fuel all its activities, and defend itself
against diseases. How successfully your body handles these tasks depends, in
part, on your food choices. Nutritious food choices support healthy bodies.
Nutrition in Your Life
Key Sanders/Getty Images
The CengageNOW logo
indicates an opportunity for
online self-study, linking you
to interactive tutorials and videos based on
your level of understanding.
academic.cengage.com/login
How To: Practice Problems
Nutrition Portfolio Journal
Nutrition Calculations: Practice Problems

Welcome to the world of nutrition. Although you may not always have
been aware of it, nutrition has played a significant role in your life. And it
will continue to affect you in major ways, depending on the foods you select.
Every day, several times a day, you make food choices that influence
your body’s health for better or worse. Each day’s choices may benefit or
harm your health only a little, but when these choices are repeated over
years and decades, the rewards or consequences become major. That being
the case, paying close attention to good eating habits now can bring you
health benefits later. Conversely, carelessness about food choices can con-
tribute to many chronic diseases ◆ prevalent in later life, including heart
disease and cancer. Of course, some people will become ill or die young no
matter what choices they make, and others will live long lives despite mak-
ing poor choices. For the majority of us, however, the food choices we make
each and every day will benefit or impair our health in proportion to the
wisdom of those choices.
Although most people realize that their food habits affect their health, they of-
ten choose foods for other reasons. After all, foods bring to the table a variety of
pleasures, traditions, and associations as well as nourishment. The challenge, then,
is to combine favorite foods and fun times with a nutritionally balanced diet.
Food Choices
People decide what to eat, when to eat, and even whether to eat in highly personal
ways, often based on behavioral or social motives rather than on an awareness of nu-
trition’s importance to health. Many different food choices can support good health,
and an understanding of nutrition helps you make sensible selections more often.
Personal Preference As you might expect, the number one reason people choose
foods is taste—they like certain flavors. Two widely shared preferences are for the
sweetness of sugar and the savoriness of salt. Liking high-fat foods also appears to be
a universally common preference. Other preferences might be for the hot peppers
3
CHAPTER OUTLINE
Food Choices
The Nutrients • Nutrients in Foods and
in the Body • The Energy-Yielding Nutri-
ents: Carbohydrate, Fat, and Protein •
The Vitamins • The Minerals • Water
The Science of Nutrition • Conducting
Research • Analyzing Research Findings •
Publishing Research
Dietary Reference Intakes • Establish-
ing Nutrient Recommendations • Estab-
lishing Energy Recommendations • Using
Nutrient Recommendations • Comparing
Nutrient Recommendations
Nutrition Assessment • Nutrition
Assessment of Individuals • Nutrition
Assessment of Populations
Diet and Health • Chronic Diseases •
Risk Factors for Chronic Diseases
HIGHLIGHT 1 Nutrition Information and
Misinformation—On the Net and in the News
1
An Overview
of Nutrition
C H A P T E R
nutrition: the science of foods and the
nutrients and other substances they contain,
and of their actions within the body
(including ingestion, digestion, absorption,
transport, metabolism, and excretion).
A broader definition includes the social,
economic, cultural, and psychological
implications of food and eating.
foods: products derived from plants or
animals that can be taken into the body
to yield energy and nutrients for the
maintenance of life and the growth
and repair of tissues.
diet: the foods and beverages a person eats
and drinks.
◆ In general, a chronic disease progresses
slowly or with little change and lasts a
long time. By comparison, an acute dis-
ease develops quickly, produces sharp
symptoms, and runs a short course.
• chronos = time
• acute = sharp

common in Mexican cooking or the curry spices of Indian cuisine. Some research sug-
gests that genetics may influence people’s food preferences.1
Habit People sometimes select foods out of habit. They eat cereal every morning,
for example, simply because they have always eaten cereal for breakfast. Eating a
familiar food and not having to make any decisions can be comforting.
Ethnic Heritage or Tradition
Among the strongest influences on food choices are ethnic heritage and tradition.
People eat the foods they grew up eating. Every country, and in fact every region of
a country, has its own typical foods and ways of combining them into meals. The
“American diet” includes many ethnic foods from various countries, all adding va-
riety to the diet. This is most evident when eating out: 60 percent of U.S. restaurants
(excluding fast-food places) have an ethnic emphasis, most commonly Chinese,
Italian, or Mexican.
Social Interactions Most people enjoy companionship while eating. It’s fun to go
out with friends for pizza or ice cream. Meals are social events, and sharing food is
part of hospitality. Social customs invite people to accept food or drink offered by a
host or shared by a group.
Availability, Convenience, and Economy People eat foods that are accessible,
quick and easy to prepare, and within their financial means. Today’s consumers
value convenience and are willing to spend more than half of their food budget on
meals that require little, if any, further preparation.2 They frequently eat out, bring
home ready-to-eat meals, or have food delivered. Even when they venture into the
kitchen, they want to prepare a meal in 15 to 20 minutes, using less than a half
dozen ingredients—and those “ingredients” are often semiprepared foods, such as
canned soups. This emphasis on convenience limits food choices to the selections of-
fered on menus and products designed for quick preparation. Whether decisions
based on convenience meet a person’s nutrition needs depends on the choices made.
Eating a banana or a candy bar may be equally convenient, but the fruit offers more
vitamins and minerals and less sugar and fat.
Positive and Negative Associations People tend to like particular foods associ-
ated with happy occasions—such as hot dogs at ball games or cake and ice cream
at birthday parties. By the same token, people can develop aversions and dislike
foods that they ate when they felt sick or that were forced on them.3 By using foods
as rewards or punishments, parents may inadvertently teach their children to like
and dislike certain foods.
Emotional Comfort Some people cannot eat when they are emotionally upset.
Others may eat in response to a variety of emotional stimuli—for example, to re-
lieve boredom or depression or to calm anxiety.4 A depressed person may choose to
eat rather than to call a friend. A person who has returned home from an exciting
evening out may unwind with a late-night snack. These people may find emotional
comfort, in part, because foods can influence the brain’s chemistry and the mind’s
response. Carbohydrates and alcohol, for example, tend to calm, whereas proteins
and caffeine are more likely to activate. Eating in response to emotions can easily
lead to overeating and obesity, but it may be appropriate at times. For example,
sharing food at times of bereavement serves both the giver’s need to provide comfort
and the receiver’s need to be cared for and to interact with others, as well as to take
nourishment.
Values Food choices may reflect people’s religious beliefs, political views, or envi-
ronmental concerns. For example, many Christians forgo meat during Lent (the
period prior to Easter), Jewish law includes an extensive set of dietary rules that
govern the use of foods derived from animals, and Muslims fast between sunrise
and sunset during Ramadan (the ninth month of the Islamic calendar). A con-
An enjoyable way to learn about other
cultures is to taste their ethnic foods.
©
Bill
Aron/PhotoEdit,
Inc.
4 • CHAPTER 1

cerned consumer may boycott fruit picked by migrant workers who have been ex-
ploited. People may buy vegetables from local farmers to save the fuel and envi-
ronmental costs of foods shipped in from far away. They may also select foods
packaged in containers that can be reused or recycled. Some consumers accept or
reject foods that have been irradiated or genetically modified, depending on their
approval of these processes.
Body Weight and Image Sometimes people select certain foods and supplements
that they believe will improve their physical appearance and avoid those they be-
lieve might be detrimental. Such decisions can be beneficial when based on sound
nutrition and fitness knowledge, but decisions based on fads or carried to extremes
undermine good health, as pointed out in later discussions of eating disorders
(Highlight 8).
Nutrition and Health Benefits Finally, of course, many consumers make food
choices that will benefit health. Food manufacturers and restaurant chefs have re-
sponded to scientific findings linking health with nutrition by offering an abun-
dant selection of health-promoting foods and beverages. Foods that provide
health benefits beyond their nutrient contributions are called functional foods.5
Whole foods—as natural and familiar as oatmeal or tomatoes—are the simplest
functional foods. In other cases, foods have been modified to provide health ben-
efits, perhaps by lowering the fat contents. In still other cases, manufacturers have
fortified foods by adding nutrients or phytochemicals that provide health ben-
efits (see Highlight 13). ◆ Examples of these functional foods include orange juice
fortified with calcium to help build strong bones and margarine made with a
plant sterol that lowers blood cholesterol.
Consumers typically welcome new foods into their diets, provided that these
foods are reasonably priced, clearly labeled, easy to find in the grocery store, and
convenient to prepare. These foods must also taste good—as good as the tradi-
tional choices. Of course, a person need not eat any of these “special” foods to en-
joy a healthy diet; many “regular” foods provide numerous health benefits as
well. In fact, “regular” foods such as whole grains; vegetables and legumes; fruits;
meats, fish, and poultry; and milk products are among the healthiest choices a
person can make.
To enhance your health, keep nutrition in
mind when selecting foods.
◆ Functional foods may include whole foods,
modified foods, or fortified foods.
A person selects foods for a variety of reasons. Whatever those reasons may be,
food choices influence health. Individual food selections neither make nor
break a diet’s healthfulness, but the balance of foods selected over time can
make an important difference to health.6 For this reason, people are wise to
think “nutrition” when making their food choices.
IN SUMMARY
The Nutrients
Biologically speaking, people eat to receive nourishment. Do you ever think of your-
self as a biological being made of carefully arranged atoms, molecules, cells, tissues,
and organs? Are you aware of the activity going on within your body even as you sit
still? The atoms, molecules, and cells of your body continually move and change,
even though the structures of your tissues and organs and your external appearance
remain relatively constant. Your skin, which has covered you since your birth, is re-
placed entirely by new cells every seven years. The fat beneath your skin is not the
functional foods: foods that contain
physiologically active compounds that
provide health benefits beyond their nutrient
contributions; sometimes called designer
foods or nutraceuticals.
phytochemicals (FIE-toe-KEM-ih-cals):
nonnutrient compounds found in plant-
derived foods that have biological activity
in the body.
• phyto = plant
©
Ariel
Skelley/CORBIS
AN OVERVIEW OF NUTRITION • 5

same fat that was there a year ago. Your oldest red blood cell
is only 120 days old, and the entire lining of your digestive
tract is renewed every 3 to 5 days. To maintain your “self,”
you must continually replenish, from foods, the energy and
the nutrients you deplete as your body maintains itself.
Nutrients in Foods and in the
Body
Amazingly, our bodies can derive all the energy, structural
materials, and regulating agents we need from the foods we
eat. This section introduces the nutrients that foods deliver
and shows how they participate in the dynamic processes
that keep people alive and well.
Composition of Foods Chemical analysis of a food such
as a tomato shows that it is composed primarily of water (95
percent). Most of the solid materials are carbohydrates,
lipids, ◆ and proteins. If you could remove these materials,
you would find a tiny residue of vitamins, minerals, and
other compounds. Water, carbohydrates, lipids, proteins, vitamins, and some of the
minerals found in foods are nutrients—substances the body uses for the growth,
maintenance, and repair of its tissues.
This book focuses mostly on the nutrients, but foods contain other compounds
as well—fibers, phytochemicals, pigments, additives, alcohols, and others. Some
are beneficial, some are neutral, and a few are harmful. Later sections of the book
touch on these compounds and their significance.
Composition of the Body A complete chemical analysis of your body would
show that it is made of materials similar to those found in foods (see Figure 1-1). A
healthy 150-pound body contains about 90 pounds of water and about 20 to 45
pounds of fat. The remaining pounds are mostly protein, carbohydrate, and the ma-
jor minerals of the bones. Vitamins, other minerals, and incidental extras constitute
a fraction of a pound.
Foods bring pleasure—and nutrients.
◆ As Chapter 5 explains, most lipids are fats.
% Carbohydrates, proteins,
vitamins, minerals in the body
Key:
% Fat in the body
% Water in the body
energy: the capacity to do work. The energy
in food is chemical energy. The body can
convert this chemical energy to mechanical,
electrical, or heat energy.
nutrients: chemical substances obtained
from food and used in the body to provide
energy, structural materials, and regulating
agents to support growth, maintenance, and
repair of the body’s tissues. Nutrients may
also reduce the risks of some diseases.
©
Masterfile
6 • CHAPTER 1
FIGURE 1-1 Body Composition of Healthy-Weight Men and Women
The human body is made of compounds similar to those found in foods—mostly
water (60 percent) and some fat (13 to 21 percent for young men, 23 to 31 percent
for young women), with carbohydrate, protein, vitamins, minerals, and other
minor constituents making up the remainder. (Chapter 8 describes the health haz-
ards of too little or too much body fat.)
© Photodisc/Getty Images

Chemical Composition of Nutrients The simplest of the nutrients are the min-
erals. Each mineral is a chemical element; its atoms are all alike. As a result, its iden-
tity never changes. For example, iron may have different electrical charges, but the
individual iron atoms remain the same when they are in a food, when a person eats
the food, when the iron becomes part of a red blood cell, when the cell is broken
down, and when the iron is lost from the body by excretion. The next simplest nu-
trient is water, a compound made of two elements—hydrogen and oxygen. Miner-
als and water are inorganic nutrients—which means they do not contain carbon.
The other four classes of nutrients (carbohydrates, lipids, proteins, and vitamins)
are more complex. In addition to hydrogen and oxygen, they all contain carbon,
an element found in all living things. They are therefore called organic ◆ com-
pounds (meaning, literally, “alive”). Protein and some vitamins also contain nitro-
gen and may contain other elements as well (see Table 1-1).
Essential Nutrients The body can make some nutrients, but it cannot make all of
them. Also, it makes some in insufficient quantities to meet its needs and, therefore,
must obtain these nutrients from foods. The nutrients that foods must supply are es-
sential nutrients. When used to refer to nutrients, the word essential means more
than just “necessary”; it means “needed from outside the body”—normally, from
foods.
The Energy-Yielding Nutrients:
Carbohydrate, Fat, and Protein
In the body, three organic nutrients can be used to provide energy: carbohydrate,
fat, and protein. ◆ In contrast to these energy-yielding nutrients, vitamins, min-
erals, and water do not yield energy in the human body.
Energy Measured in kCalories The energy released from carbohydrates, fats,
and proteins can be measured in calories—tiny units of energy so small that a sin-
gle apple provides tens of thousands of them. To ease calculations, energy is expressed
in 1000-calorie metric units known as kilocalories (shortened to kcalories, but com-
monly called “calories”). When you read in popular books or magazines that an ap-
ple provides “100 calories,” it actually means 100 kcalories. This book uses the term
kcalorie and its abbreviation kcal throughout, as do other scientific books and jour-
nals. ◆ The “How to” on p. 8 provides a few tips on “thinking metric.”
TABLE 1-1 Elements in the Six Classes of Nutrients
Notice that organic nutrients contain carbon.
Carbon Hydrogen Oxygen Nitrogen Minerals
Inorganic nutrients
Minerals ✓
Water ✓ ✓
Organic nutrients
Carbohydrates ✓ ✓ ✓
Lipids (fats) ✓ ✓ ✓
Proteinsa ✓ ✓ ✓ ✓
Vitaminsb ✓ ✓ ✓
aSome proteins also contain the mineral sulfur.
bSome vitamins contain nitrogen; some contain minerals.
◆ In agriculture, organic farming refers to
growing crops and raising livestock accord-
ing to standards set by the U.S. Department
of Agriculture (USDA).
◆ Carbohydrate, fat, and protein are
sometimes called macronutrients because
the body requires them in relatively large
amounts (many grams daily). In contrast, vi-
tamins and minerals are micronutrients,
required only in small amounts (milligrams
or micrograms daily).
◆ The international unit for measuring food
energy is the joule, a measure of work
energy. To convert kcalories to kilojoules,
multiply by 4.2; to convert kilojoules to
kcalories, multiply by 0.24.
inorganic: not containing carbon or
pertaining to living things.
• in = not
organic: in chemistry, a substance or
molecule containing carbon-carbon bonds
or carbon-hydrogen bonds. This definition
excludes coal, diamonds, and a few carbon-
containing compounds that contain only a
single carbon and no hydrogen, such as
carbon dioxide (CO2), calcium carbonate
(CaCO3), magnesium carbonate (MgCO3),
and sodium cyanide (NaCN).
essential nutrients: nutrients a person must
obtain from food because the body cannot
make them for itself in sufficient quantity
to meet physiological needs; also called
indispensable nutrients. About 40
nutrients are currently known to be
essential for human beings.
energy-yielding nutrients: the nutrients
that break down to yield energy the body
can use:
• Carbohydrate
• Fat
• Protein
calories: units by which energy is measured.
Food energy is measured in kilocalories
(1000 calories equal 1 kilocalorie),
abbreviated kcalories or kcal. One kcalorie
is the amount of heat necessary to raise the
temperature of 1 kilogram (kg) of water 1°C.
The scientific use of the term kcalorie is the
same as the popular use of the term calorie.

8 • CHAPTER 1
Energy from Foods The amount of energy a food provides depends on how much
carbohydrate, fat, and protein it contains. When completely broken down in the body,
a gram of carbohydrate yields about 4 kcalories of energy; a gram of protein also
yields 4 kcalories; and a gram of fat yields 9 kcalories (see Table 1-2). Fat, therefore, has
a greater energy density than either carbohydrate or protein. Figure 1-2 compares
the energy density of two breakfast options, and later chapters describe how consider-
ing a food’s energy density can help with weight management. ◆ The “How to” on
p. 9 explains how to calculate the energy available from foods.
One other substance contributes energy—alcohol. Alcohol is not considered a
nutrient because it interferes with the growth, maintenance, and repair of the body,
but it does yield energy (7 kcalories per gram) when metabolized in the body. (High-
light 7 presents alcohol metabolism; Chapter 27 mentions the potential harmful
role of alcohol in hypertension and the possible beneficial role in heart disease.)
Like other scientists, nutrition scientists use
metric units of measure. They measure food
energy in kilocalories, people’s height in cen-
timeters, people’s weight in kilograms, and the
weights of foods and nutrients in grams, mil-
ligrams, or micrograms. For ease in using these
measures, it helps to remember that the prefixes
on the grams imply 1000. For example, a kilo-
gram is 1000 grams, a milligram is 1/1000 of a
gram, and a microgram is 1/1000 of a milligram.
Most food labels and many recipe books
provide “dual measures,” listing both household
measures, such as cups, quarts, and teaspoons,
and metric measures, such as milliliters, liters,
and grams. This practice gives people an oppor-
tunity to gradually learn to “think metric.”
A person might begin to “think metric” by
simply observing the measure—by noticing the
amount of soda in a 2-liter bottle, for example.
Through such experiences, a person can be-
come familiar with a measure without having to
do any conversions.
To facilitate communication, many members
of the international scientific community have
adopted a common system of measurement—
the International System of Units (SI). In addition
to using metric measures, the SI establishes
common units of measurement. For example,
the SI unit for measuring food energy is the joule
(not the kcalorie). A joule is the amount of
energy expended when 1 kilogram is moved 1
meter by a force of 1 newton. The joule is thus a
measure of work energy, whereas the kcalorie is
a measure of heat energy. While many scientists
and journals report their findings in kilojoules
(kJ), many others, particularly those in the
United States, use kcalories (kcal). To convert
energy measures from kcalories to kilojoules,
multiply by 4.2. For example, a 50-kcalorie
cookie provides 210 kilojoules:
50 kcal 4.2 210 kJ
Exact conversion factors for these and other units
of measure are in the Aids to Calculation section
on the last two pages of the book.
HOW TO Think Metric
Volume: Liters (L)
1 L 1000 milliliters (mL)
0.95 L 1 quart
1 mL 0.03 fluid ounces
240 mL 1 cup
A liter of liquid is approximately one U.S.
quart. (Four liters are only about 5 percent
more than a gallon.)
One cup is about 240 milliliters; a half-cup of
liquid is about 120 milliliters.
©
Felicia
Martinez/Photo
Edit
©
PhotoEdit/Felicia
Martinez
Weight: Grams (g)
1 g 1000 milligrams (mg)
1 g 0.04 ounce (oz)
1 oz 28.35 g (or 30 g)
100 g 31
⁄2 oz
1 kilogram (kg) 1000 g
1 kg 2.2 pounds (lb)
454 g 1 lb
A half-cup of vegetables weighs about 100
grams; one pea weighs about 1
⁄2 gram.
A 5-pound bag of potatoes weighs about 2
kilograms, and a 176-pound person weighs
80 kilograms.
©
Thomas
Harm,
Tom
Peterson/
Quest
Photographic
Inc.
©
Tony
Freeman/Photo
Edit
A kilogram is slightly more than 2 lb;
conversely, a pound is about 1
⁄2 kg.
energy density: a measure of the energy a
food provides relative to the amount of food
(kcalories per gram).
◆ Foods with a high energy density help with
weight gain, whereas those with a low
energy density help with weight loss.
To practice thinking metrically, log on to
academic.cengage.com/login, go to
Chapter 1, then go to How To.

FIGURE 1-2 Energy Density of Two Breakfast Options Compared
Gram for gram, ounce for ounce, and bite for bite, foods with a high energy density deliver more
kcalories than foods with a low energy density. Both of these breakfast options provide 500 kcalories,
but the cereal with milk, fruit salad, scrambled egg, turkey sausage, and toast with jam offers three
times as much food as the doughnuts (based on weight); it has a lower energy density than the
doughnuts. Selecting a variety of foods also helps to ensure nutrient adequacy.
Most foods contain all three energy-yielding nutrients, as well as water, vita-
mins, minerals, and other substances. For example, meat contains water, fat, vita-
mins, and minerals as well as protein. Bread contains water, a trace of fat, a little
protein, and some vitamins and minerals in addition to its carbohydrate. Only a
few foods are exceptions to this rule, the common ones being sugar (pure carbohy-
drate) and oil (essentially pure fat).
Energy in the Body The body uses the energy-yielding nutrients to fuel all its activ-
ities. When the body uses carbohydrate, fat, or protein for energy, the bonds between
LOWER ENERGY DENSITY
This 450-gram breakfast delivers 500 kcalories,
for an energy density of 1.1
(500 kcal 450 g 1.1 kcal/g).
HIGHER ENERGY DENSITY
This 144-gram breakfast delivers 500 kcalories,
for an energy density of 3.5
(500 kcal 144 g 3.5 kcal/g).
©
Matthew
Farruggio
(both)
To calculate the energy available from a
food, multiply the number of grams of
carbohydrate, protein, and fat by 4, 4,
and 9, respectively. Then add the results
together. For example, 1 slice of bread
with 1 tablespoon of peanut butter on it
contains 16 grams carbohydrate, 7
grams protein, and 9 grams fat:
16 g carbohydrate 4 kcal/g 64 kcal
7 g protein 4 kcal/g 28 kcal
9 g fat 9 kcal/g 81 kcal
Total 173 kcal
From this information, you can calculate
the percentage of kcalories each of the
energy nutrients contributes to the total.
To determine the percentage of kcalories
from fat, for example, divide the 81 fat
kcalories by the total 173 kcalories:
81 fat kcal 173 total kcal 0.468
(rounded to 0.47)
Then multiply by 100 to get the percentage:
0.47 100 47%
Dietary recommendations that urge
people to limit fat intake to 20 to 35
percent of kcalories refer to the day’s total
energy intake, not to individual foods.
Still, if the proportion of fat in each food
choice throughout a day exceeds 35
percent of kcalories, then the day’s total
surely will, too. Knowing that this snack
provides 47 percent of its kcalories from
fat alerts a person to the need to make
lower-fat selections at other times that
day.
HOW TO Calculate the Energy Available from Foods
TABLE 1-2 kCalorie Values
of Energy Nutrientsa
Nutrients Energy
(kcal/g)
Carbohydrate 4
Fat 9
Protein 4
NOTE: Alcohol contributes 7 kcalories per gram that can be used
for energy, but it is not considered a nutrient because it interferes
with the body’s growth, maintenance, and repair.
a For those using kilojoules: 1 g carbohydrate 17 kJ; 1 g protein
17 kJ; 1 g fat 37 kJ; and 1 g alcohol 29 kJ.
To practice calculating the energy available from
foods, log on to academic.cengage.com/login,
go to Chapter 1, then go to How To.

10 • CHAPTER 1
the nutrient’s atoms break. As the bonds break, they release energy. ◆ Some of this en-
ergy is released as heat, but some is used to send electrical impulses through the brain
and nerves, to synthesize body compounds, and to move muscles. Thus the energy
from food supports every activity from quiet thought to vigorous sports.
If the body does not use these nutrients to fuel its current activities, it rearranges them
into storage compounds (such as body fat), to be used between meals and overnight
when fresh energy supplies run low. If more energy is consumed than expended, the re-
sult is an increase in energy stores and weight gain. Similarly, if less energy is consumed
than expended, the result is a decrease in energy stores and weight loss.
When consumed in excess of energy needs, alcohol, too, can be converted to
body fat and stored. When alcohol contributes a substantial portion of the energy
in a person’s diet, the harm it does far exceeds the problems of excess body fat.
(Highlight 7 describes the effects of alcohol on health and nutrition.)
Other Roles of Energy-Yielding Nutrients In addition to providing energy,
carbohydrates, fats, and proteins provide the raw materials for building the body’s
tissues and regulating its many activities. In fact, protein’s role as a fuel source is rel-
atively minor compared with both the other two nutrients and its other roles. Pro-
teins are found in structures such as the muscles and skin and help to regulate
activities such as digestion and energy metabolism.
The Vitamins
The vitamins are also organic, but they do not provide energy. Instead, they facili-
tate the release of energy from carbohydrate, fat, and protein and participate in nu-
merous other activities throughout the body.
Each of the 13 different vitamins has its own special roles to play.* One vitamin
enables the eyes to see in dim light, another helps protect the lungs from air pollu-
tion, and still another helps make the sex hormones—among other things. When
you cut yourself, one vitamin helps stop the bleeding and another helps repair the
skin. Vitamins busily help replace old red blood cells and the lining of the digestive
tract. Almost every action in the body requires the assistance of vitamins.
Vitamins can function only if they are intact, but because they are complex or-
ganic molecules, they are vulnerable to destruction by heat, light, and chemical
agents. This is why the body handles them carefully, and why nutrition-wise cooks
do, too. The strategies of cooking vegetables at moderate temperatures for short
times and using small amounts of water help to preserve the vitamins.
The Minerals
In the body, some minerals are put together in orderly arrays in such structures as
bones and teeth. Minerals are also found in the fluids of the body, which influences
fluid properties. Whatever their roles, minerals do not yield energy.
Only 16 minerals are known to be essential in human nutrition.† Others are be-
ing studied to determine whether they play significant roles in the human body.
Still other minerals are environmental contaminants that displace the nutrient
minerals from their workplaces in the body, disrupting body functions. The prob-
lems caused by contaminant minerals are described in Chapter 13.
Because minerals are inorganic, they are indestructible and need not be handled
with the special care that vitamins require. Minerals can, however, be bound by sub-
stances that interfere with the body’s ability to absorb them. They can also be lost dur-
ing food-refining processes or during cooking when they leach into water that is
discarded.
◆ The processes by which nutrients are broken
down to yield energy or used to make body
structures are known as metabolism
(defined and described further in Chapter 7).
vitamins: organic, essential nutrients
required in small amounts by the body
for health.
minerals: inorganic elements. Some minerals
are essential nutrients required in small
amounts by the body for health.
* The water-soluble vitamins are vitamin C and the eight B vitamins: thiamin, riboflavin, niacin, vitamins
B6 and B12, folate, biotin, and pantothenic acid. The fat-soluble vitamins are vitamins A, D, E, and K. The
water-soluble vitamins are the subject of Chapter 10 and the fat-soluble vitamins, of Chapter 11.
† The major minerals are calcium, phosphorus, potassium, sodium, chloride, magnesium, and sul-
fate. The trace minerals are iron, iodine, zinc, chromium, selenium, fluoride, molybdenum, copper,
and manganese. Chapters 12 and 13 are devoted to the major and trace minerals, respectively.

Water
Water, indispensable and abundant, provides the environment in which nearly
all the body’s activities are conducted. It participates in many metabolic reac-
tions and supplies the medium for transporting vital materials to cells and car-
rying waste products away from them. Water is discussed fully in Chapter 12,
but it is mentioned in every chapter. If you watch for it, you cannot help but be
impressed by water’s participation in all life processes.
Water itself is an essential nutrient and natu-
rally carries many minerals.
Foods provide nutrients—substances that support the growth, maintenance,
and repair of the body’s tissues. The six classes of nutrients include:
· Carbohydrates
· Lipids (fats)
· Proteins
· Vitamins
· Minerals
· Water
Foods rich in the energy-yielding nutrients (carbohydrates, fats, and proteins)
provide the major materials for building the body’s tissues and yield energy for
the body’s use or storage. Energy is measured in kcalories. Vitamins, minerals,
and water facilitate a variety of activities in the body.
IN SUMMARY
The Science of Nutrition
The science of nutrition is the study of the nutrients and other substances in foods
and the body’s handling of them. Its foundation depends on several other sciences,
including biology, biochemistry, and physiology. As sciences go, nutrition is young,
but as you can see from the size of this book, much has happened in nutrition’s short
life. And it is currently entering a tremendous growth spurt as scientists apply
knowledge gained from sequencing the human genome. The integration of nutri-
tion, genomics, and molecular biology has opened a whole new world of study
called nutritional genomics—the science of how nutrients affect the activities of
genes and how genes affect the interactions between diet and disease.7 Highlight 6
describes how nutritional genomics is shaping the science of nutrition, and exam-
ples of nutrient–gene interactions appear throughout later sections of the book.
Conducting Research
Consumers may depend on personal experience or reports from friends ◆ to gather
information on nutrition, but researchers use the scientific method to guide their work
(see Figure 1-3 on p. 12). As the figure shows, research always begins with a problem or
a question. For example, “What foods or nutrients might protect against the common
cold?” In search of an answer, scientists make an educated guess (hypothesis), such as
“foods rich in vitamin C reduce the number of common colds.” Then they systematically
conduct research studies to collect data that will test the hypothesis (see the glossary on
p. 14 for definitions of research terms). Some examples of various types of research de-
signs are presented in Figure 1-4 (p. 13). Each type of study has strengths and weaknesses
(see Table 1-3 on p. 14). Consequently, some provide stronger evidence than others.
◆ A personal account of an experience or event
is an anecdote and is not accepted as reli-
able scientific information.
• anekdotos = unpublished
genome (GEE-nome): the full complement of
genetic material (DNA) in the chromosomes
of a cell. In human beings, the genome
consists of 46 chromosomes. The study
of genomes is called genomics.
nutritional genomics: the science of how
nutrients affect the activities of genes
(nutrigenomics) and how genes affect
the interactions between diet and disease
(nutrigenetics).
©
Corbis
Without exaggeration, nutrients provide the physical and metabolic basis for
nearly all that we are and all that we do. The next section introduces the science
of nutrition with emphasis on the research methods scientists have used in uncov-
ering the wonders of nutrition.

In attempting to discover whether a nutrient relieves
symptoms or cures a disease, researchers deliberately manip-
ulate one variable (for example, the amount of vitamin C in
the diet) and measure any observed changes (perhaps the
number of colds). As much as possible, all other conditions
are held constant. The following paragraphs illustrate how
this is accomplished.
Controls In studies examining the effectiveness of vitamin
C, researchers typically divide the subjects into two groups.
One group (the experimental group) receives a vitamin C
supplement, and the other (the control group) does not. Re-
searchers observe both groups to determine whether one
group has fewer or shorter colds than the other. The following
discussion describes some of the pitfalls inherent in an exper-
iment of this kind and ways to avoid them.
In sorting subjects into two groups, researchers must en-
sure that each person has an equal chance of being assigned
to either the experimental group or the control group. This is
accomplished by randomization; that is, the subjects are
chosen randomly from the same population by flipping a
coin or some other method involving chance. Randomiza-
tion helps to ensure that results reflect the treatment and not
factors that might influence the grouping of subjects.
Importantly, the two groups of people must be similar and
must have the same track record with respect to colds to rule out
the possibility that observed differences in the rate, severity, or
duration of colds might have occurred anyway. If, for example,
the control group would normally catch twice as many colds as
the experimental group, then the findings prove nothing.
In experiments involving a nutrient, the diets of both
groups must also be similar, especially with respect to the nu-
trient being studied. If those in the experimental group were
receiving less vitamin C from their usual diet, then any ef-
fects of the supplement may not be apparent.
Sample Size To ensure that chance variation between the
two groups does not influence the results, the groups must
be large. For example, if one member of a group of five peo-
ple catches a bad cold by chance, he will pull the whole
group’s average toward bad colds; but if one member of a
group of 500 catches a bad cold, she will not unduly affect
the group average. Statistical methods are used to determine whether differences
between groups of various sizes support a hypothesis.
Placebos If people who take vitamin C for colds believe it will cure them, their
chances of recovery may improve. Taking anything believed to be beneficial may has-
ten recovery. This phenomenon, the result of expectations, is known as the placebo
effect. In experiments designed to determine vitamin C’s effect on colds, this mind-
body effect must be rigorously controlled. Severity of symptoms is often a subjective
measure, and people who believe they are receiving treatment may report less severe
symptoms.
One way experimenters control for the placebo effect is to give pills to all partic-
ipants. Those in the experimental group, for example, receive pills containing vita-
min C, and those in the control group receive a placebo—pills of similar
appearance and taste containing an inactive ingredient. This way, the expecta-
tions of both groups will be equal. It is not necessary to convince all subjects that
they are receiving vitamin C, but the extent of belief or unbelief must be the same
in both groups. A study conducted under these conditions is called a blind exper-
Formulate a hypothesis—a tentative
solution to the problem or answer to
the question—and make a prediction
that can be tested.
HYPOTHESIS PREDICTION
Identify a problem to be solved or ask
a specific question to be answered.
OBSERVATION QUESTION
Design a study and conduct the
research to collect relevant data.
EXPERIMENT
Summarize, analyze, and interpret
the data; draw conclusions.
RESULTS INTERPRETATIONS
HYPOTHESIS NOT SUPPORTED
HYPOTHESIS SUPPORTED
Develop a theory that integrates
conclusions with those from
numerous other studies.
THEORY NEW OBSERVATIONS
QUESTIONS
FIGURE 1-3 The Scientific Method
Research scientists follow the scientific method. Note that most
research generates new questions, not final answers. Thus the
sequence begins anew, and research continues in a somewhat
cyclical way.
12 • CHAPTER 1

North
Atlantic
Ocean
Mediterranean Sea
Black Sea
France
Spain
Morocco
Algeria
Libya
Tunisia
Italy
Greece Turkey
Croatia
Slovenia
Albania
Egypt
Syria
Jordan
Israel
Lebanon
Montenegro
Bosnia
EPIDEMIOLOGICAL STUDIES
EXPERIMENTAL STUDIES
Blood cholesterol
Heart
attacks
Example. The people of the Mediterranean
region drink lots of wine, eat plenty of fat
from olive oil, and have a lower incidence
of heart disease than northern Europeans
and North Americans.
Example. People with goiter lack iodine
in their diets.
Researchers observe how much and what
kinds of foods a group of people eat and
how healthy those people are. Their findings
identify factors that might influence the
incidence of a disease in various
populations. Researchers compare people who do and
do not have a given condition such as a
disease, closely matching them in age,
gender, and other key variables so that
differences in other factors will stand out.
These differences may account for the
condition in the group that has it.
Example. Data collected periodically over
the past several decades from over 5000
people randomly selected from the town of
Framingham, Massachusetts, in 1948 have
revealed that the risk of heart attack
increases as blood cholesterol increases.
Researchers analyze data collected from a
selected group of people (a cohort) at
intervals over a certain period of time.
Example. Heart disease risk factors
improve when men receive fresh-squeezed
orange juice daily for two months
compared with those on a diet low in
vitamin C—even when both groups follow a
diet high in saturated fat.
Example. Laboratory studies find that fish
oils inhibit the growth and activity of the
bacteria implicated in ulcer formation.
Researchers ask people to adopt a new
behavior (for example, eat a citrus fruit, take
a vitamin C supplement, or exercise daily).
These trials help determine the
effectiveness of such interventions on the
development or prevention of disease.
Researchers feed animals special diets
that provide or omit specific nutrients and
then observe any changes in health. Such
studies test possible disease causes and
treatments in a laboratory where all
conditions can be controlled.
Example. Mice fed a high-fat diet eat less
food than mice given a lower-fat diet, so
they receive the same number of
kcalories—but the mice eating the fat-rich
diet become severely obese.
Researchers examine the effects of a
specific variable on a tissue, cell, or
molecule isolated from a living organism.
HUMAN INTERVENTION
(OR CLINICAL) TRIALS
LABORATORY-BASED
ANIMAL STUDIES
LABORATORY-BASED
IN VITRO STUDIES
CASE-CONTROL
CROSS-SECTIONAL COHORT
©
R.
Benali/Getty
Images
©
PhotoDisc/Getty
Images
USDA
Agricultural
Research
Service
©
L.
V.
Bergman
and
Associates
Inc.
Corbis
iment—that is, the subjects do not know (are blind to) whether they are members
of the experimental group (receiving treatment) or the control group (receiving the
placebo).
Double Blind When both the subjects and the researchers do not know which sub-
jects are in which group, the study is called a double-blind experiment. Being fal-
lible human beings and having an emotional and sometimes financial investment
FIGURE 1-4 Examples of Research Designs

14 • CHAPTER 1
TABLE 1-3 Strengths and Weaknesses of Research Designs
Type of Research Strengths Weaknesses
Epidemiological studies
determine the incidence and
distribution of diseases in a
population. Epidemiological
studies include cross-sectional,
case-control, and cohort (see
Figure 1-4).
Laboratory-based studies
explore the effects of a specific
variable on a tissue, cell, or
molecule. Laboratory-based
studies are often conducted in
test tubes (in vitro) or on
animals.
Human intervention or clini-
cal trials involve human beings
who follow a specified regimen.
• Can narrow down the list of
possible causes
• Can raise questions to pur-
sue through other types of
studies
• Can control conditions
• Can determine effects of a
variable
• Can control conditions (for
the most part)
• Can apply findings to some
groups of human beings
• Cannot control variables
that may influence the
development or the
prevention of a disease
• Cannot prove cause and
effect
• Cannot apply results from
test tubes or animals to
human beings
• Cannot generalize findings
to all human beings
• Cannot use certain treat-
ments for clinical or ethical
reasons
in a successful outcome, researchers might record and interpret results with a bias in
the expected direction. To prevent such bias, the pills would be coded by a third
party, who does not reveal to the experimenters which subjects were in which group
until all results have been recorded.
Analyzing Research Findings
Research findings must be analyzed and interpreted with an awareness of each
study’s limitations. Scientists must be cautious about drawing any conclusions until
they have accumulated a body of evidence from multiple studies that have used var-
ious types of research designs. As evidence accumulates, scientists begin to develop a
theory that integrates the various findings and explains the complex relationships.
blind experiment: an experiment
in which the subjects do not
know whether they are
members of the experimental
group or the control group.
control group: a group of
individuals similar in all possible
respects to the experimental
group except for the treatment.
Ideally, the control group receives
a placebo while the experimental
group receives a real treatment.
correlation (CORE-ee-LAY-shun):
the simultaneous increase,
decrease, or change in two
variables. If A increases as B
increases, or if A decreases as B
decreases, the correlation is
positive. (This does not mean
that A causes B or vice versa.) If
A increases as B decreases, or if A
decreases as B increases, the
correlation is negative. (This
does not mean that A prevents B
or vice versa.) Some third factor
may account for both A and B.
double-blind experiment: an
experiment in which neither the
subjects nor the researchers
know which subjects are
members of the experimental
group and which are serving as
control subjects, until after the
experiment is over.
experimental group: a group of
individuals similar in all possible
respects to the control group
except for the treatment. The
experimental group receives the
real treatment.
hypothesis (hi-POTH-eh-sis):
an unproven statement that
tentatively explains the
relationships between two
or more variables.
peer review: a process in which
a panel of scientists rigorously
evaluates a research study to
assure that the scientific method
was followed.
placebo (pla-SEE-bo): an inert,
harmless medication given to
provide comfort and hope;
a sham treatment used in
controlled research studies.
placebo effect: a change that
occurs in reponse to expectations
in the effectiveness of a treat-
ment that actually has no
pharmaceutical effects.
randomization (RAN-dom-ih-
ZAY-shun): a process of
choosing the members of the
experimental and control
groups without bias.
replication (REP-lih-KAY-shun):
repeating an experiment and
getting the same results. The
skeptical scientist, on hearing of
a new, exciting finding, will ask,
“Has it been replicated yet?” If
it hasn’t, the scientist will
withhold judgment regarding
the finding’s validity.
subjects: the people or animals
participating in a research project.
theory: a tentative explanation
that integrates many and
diverse findings to further
the understanding of a
defined topic.
validity (va-LID-ih-tee): having
the quality of being founded on
fact or evidence.
variables: factors that change. A
variable may depend on another
variable (for example, a child’s
height depends on his age), or
it may be independent (for
example, a child’s height does
not depend on the color of her
eyes). Sometimes both variables
correlate with a third variable
(a child’s height and eye color
both depend on genetics).
GLOSSARY OF RESEARCH TERMS
Knowledge about the nutrients and their
effects on health comes from scientific study. ©
Craig
M.
Moore

Correlations and Causes Researchers often examine the relationships be-
tween two or more variables—for example, daily vitamin C intake and the
number of colds or the duration and severity of cold symptoms. Importantly, re-
searchers must be able to observe, measure, or verify the variables selected. Find-
ings sometimes suggest no correlation between variables (regardless of the
amount of vitamin C consumed, the number of colds remains the same). Other
times, studies find either a positive correlation (the more vitamin C, the more
colds) or a negative correlation (the more vitamin C, the fewer colds). Corre-
lational evidence proves only that variables are associated, not that one is the
cause of the other. People often jump to conclusions when they notice correla-
tions, but their conclusions are often wrong. To actually prove that A causes B,
scientists have to find evidence of the mechanism—that is, an explanation of how
A might cause B.
Cautious Conclusions When researchers record and analyze the results of their
experiments, they must exercise caution in their interpretation of the findings. For
example, in an epidemiological study, scientists may use a specific segment of the
population—say, men 18 to 30 years old. When the scientists draw conclusions,
they are careful not to generalize the findings to all people. Similarly, scientists per-
forming research studies using animals are cautious in applying their findings to
human beings. Conclusions from any one research study are always tentative and
take into account findings from studies conducted by other scientists as well. As ev-
idence accumulates, scientists gain confidence about making recommendations
that affect people’s health and lives. Still, their statements are worded cautiously,
such as “A diet high in fruits and vegetables may protect against some cancers.”
Quite often, as scientists approach an answer to one research question, they
raise several more questions, so future research projects are never lacking. Further
scientific investigation then seeks to answer questions such as “What substance or
substances within fruits and vegetables provide protection?” If those substances
turn out to be the vitamins found so abundantly in fresh produce, then, “How
much is needed to offer protection?” “How do these vitamins protect against can-
cer?” “Is it their action as antioxidant nutrients?” “If not, might it be another ac-
tion or even another substance that accounts for the protection fruits and
vegetables provide against cancer?” (Highlight 11 explores the answers to these
questions and reviews recent research on antioxidant nutrients and disease.)
Publishing Research
The findings from a research study are submitted to a board of reviewers composed
of other scientists who rigorously evaluate the study to assure that the scientific
method was followed—a process known as peer review. The reviewers critique the
study’s hypothesis, methodology, statistical significance, and conclusions. If the re-
viewers consider the conclusions to be well supported by the evidence—that is, if the
research has validity—they endorse the work for publication in a scientific journal
where others can read it. This raises an important point regarding information
found on the Internet: much gets published without the rigorous scrutiny of peer re-
view. Consequently, readers must assume greater responsibility for examining the
data and conclusions presented—often without the benefit of journal citations.
Even when a new finding is published or released to the media, it is still only pre-
liminary and not very meaningful by itself. Other scientists will need to confirm or
disprove the findings through replication. To be accepted into the body of nutri-
tion knowledge, a finding must stand up to rigorous, repeated testing in experi-
ments performed by several different researchers. What we “know” in nutrition
results from years of replicating study findings. Communicating the latest finding
in its proper context without distorting or oversimplifying the message is a chal-
lenge for scientists and journalists alike.
With each report from scientists, the field of nutrition changes a little—each
finding contributes another piece to the whole body of knowledge. People who

16 • CHAPTER 1
know how science works understand that single findings, like single frames in a
movie, are just small parts of a larger story. Over years, the picture of what is “true”
in nutrition gradually changes, and dietary recommendations change to reflect the
current understanding of scientific research. Highlight 5 provides a detailed look at
how dietary fat recommendations have evolved over the past several decades as re-
searchers have uncovered the relationships between the various kinds of fat and
their roles in supporting or harming health.
Scientists learn about nutrition by conducting experiments that follow the
protocol of scientific research. Researchers take care to establish similar con-
trol and experimental groups, large sample sizes, placebos, and blind treat-
ments. Their findings must be reviewed and replicated by other scientists
before being accepted as valid.
IN SUMMARY
The characteristics of well-designed research have enabled scientists to study the ac-
tions of nutrients in the body. Such research has laid the foundation for quantify-
ing how much of each nutrient the body needs.
Dietary Reference Intakes
Using the results of thousands of research studies, nutrition experts have produced a
set of standards that define the amounts of energy, nutrients, other dietary compo-
nents, and physical activity that best support health. These recommendations are
called Dietary Reference Intakes (DRI), and they reflect the collaborative efforts
of researchers in both the United States and Canada.*8 The inside front covers of this
book provide a handy reference for DRI values.
Establishing Nutrient Recommendations
The DRI Committee consists of highly qualified scientists who base their estimates of
nutrient needs on careful examination and interpretation of scientific evidence.
These recommendations apply to healthy people and may not be appropriate for
people with diseases that increase or decrease nutrient needs. The next several para-
graphs discuss specific aspects of how the committee goes about establishing the val-
ues that make up the DRI:
• Estimated Average Requirements (EAR)
• Recommended Dietary Allowances (RDA)
• Adequate Intakes (AI)
• Tolerable Upper Intake Levels (UL)
Estimated Average Requirements (EAR) The committee reviews hundreds of
research studies to determine the requirement for a nutrient—how much is needed
in the diet. The committee selects a different criterion for each nutrient based on its
various roles in performing activities in the body and in reducing disease risks.
An examination of all the available data reveals that each person’s body is
unique and has its own set of requirements. Men differ from women, and needs
change as people grow from infancy through old age. For this reason, the commit-
tee clusters its recommendations for people into groups based on age and gender.
Even so, the exact requirements for people of the same age and gender are likely to
be different. For example, person A might need 40 units of a particular nutrient
each day; person B might need 35; and person C, 57. Looking at enough people
might reveal that their individual requirements fall into a symmetrical distribution,
Don’t let the DRI “alphabet soup” of nutrient
intake standards confuse you. Their names
make sense when you learn their purposes.
Dietary Reference Intakes (DRI): a set of
nutrient intake values for healthy people in
the United States and Canada. These values
are used for planning and assessing diets and
include:
• Estimated Average Requirements (EAR)
• Recommended Dietary Allowances (RDA)
• Adequate Intakes (AI)
• Tolerable Upper Intake Levels (UL)
requirement: the lowest continuing intake of
a nutrient that will maintain a specified
criterion of adequacy.
©
PhotoDisc/Getty
Images
* The DRI reports are produced by the Food and Nutrition Board, Institute of Medicine of the National
Academies, with active involvement of scientists from Canada.

with most near the midpoint and only a few at the extremes (see the left side of Fig-
ure 1-5). Using this information, the committee determines an Estimated Aver-
age Requirement (EAR) for each nutrient—the average amount that appears
sufficient for half of the population. In Figure 1-5, the Estimated Average Require-
ment is shown as 45 units.
Recommended Dietary Allowances (RDA) Once a nutrient requirement is es-
tablished, the committee must decide what intake to recommend for everybody—the
Recommended Dietary Allowance (RDA). As you can see by the distribution in
Figure 1-5, the Estimated Average Requirement (shown in the figure as 45 units) is
probably closest to everyone’s need. However, if people consumed exactly the aver-
age requirement of a given nutrient each day, half of the population would develop
deficiencies of that nutrient—in Figure 1-5, for example, person C would be among
them. Recommendations are therefore set high enough above the Estimated Aver-
age Requirement to meet the needs of most healthy people.
Small amounts above the daily requirement do no harm, whereas amounts below
the requirement may lead to health problems. When people’s nutrient intakes are
consistently deficient (less than the requirement), their nutrient stores decline, and
over time this decline leads to poor health and deficiency symptoms. Therefore, to en-
sure that the nutrient RDA meet the needs of as many people as possible, the RDA are
set near the top end of the range of the population’s estimated requirements.
In this example, a reasonable RDA might be 63 units a day (see the right side of
Figure 1-5). Such a point can be calculated mathematically so that it covers about
98 percent of a population. Almost everybody—including person C whose needs
were higher than the average—would be covered if they met this dietary goal. Rel-
atively few people’s requirements would exceed this recommendation, and even
then, they wouldn’t exceed by much.
Adequate Intakes (AI) For some nutrients, there is insufficient scientific evidence
to determine an Estimated Average Requirement (which is needed to set an RDA). In
these cases, the committee establishes an Adequate Intake (AI) instead of an
RDA. An AI reflects the average amount of a nutrient that a group of healthy peo-
ple consumes. Like the RDA, the AI may be used as nutrient goals for individuals.
20 30 40 50 60 70
Daily requirement for nutrient X (units/day)
Number
of
people
B
A
C
20 30 40 50 60 70
Daily requirement for nutrient X (units/day)
Number
of
people
B
A
C
RDA
EAR
Estimated Average
Requirement (EAR)
Each square in the graph above
represents a person with unique
nutritional requirements. (The text
discusses three of these people—A, B,
and C.) Some people require only a
small amount of nutrient X and some
require a lot. Most people, however, fall
somewhere in the middle. This amount
that covers half of the population is
called the Estimated Average
Requirement (EAR) and is represented
here by the red line.
The Recommended Dietary Allowance
(RDA) for a nutrient (shown here in
purple) is set well above the EAR,
covering about 98% of the population.
FIGURE 1-5 Estimated Average Requirements (EAR) and Recommended
Dietary Allowances (RDA) Compared
Estimated Average Requirement (EAR):
the average daily amount of a nutrient that
will maintain a specific biochemical or
physiological function in half the healthy
people of a given age and gender group.
Recommended Dietary Allowance
(RDA): the average daily amount of a
nutrient considered adequate to meet the
known nutrient needs of practically all
healthy people; a goal for dietary intake by
individuals.
deficient: the amount of a nutrient below
which almost all healthy people can be
expected, over time, to experience
deficiency symptoms.
Adequate Intake (AI): the average daily
amount of a nutrient that appears sufficient
to maintain a specified criterion; a value used
as a guide for nutrient intake when an RDA
cannot be determined.

18 • CHAPTER 1
Although both the RDA and the AI serve as nutrient intake goals for individu-
als, their differences are noteworthy. An RDA for a given nutrient is based on
enough scientific evidence to expect that the needs of almost all healthy people will
be met. An AI, on the other hand, must rely more heavily on scientific judgments
because sufficient evidence is lacking. The percentage of people covered by an AI is
unknown; an AI is expected to exceed average requirements, but it may cover more
or fewer people than an RDA would cover (if an RDA could be determined). For
these reasons, AI values are more tentative than RDA. The table on the inside front
cover identifies which nutrients have an RDA and which have an AI. Later chap-
ters present the RDA and AI values for the vitamins and minerals.
Tolerable Upper Intake Levels (UL) As mentioned earlier, the recommended in-
takes for nutrients are generous, and they do not necessarily cover every individual
for every nutrient. Nevertheless, it is probably best not to exceed these recommenda-
tions by very much or very often. Individual tolerances for high doses of nutrients
vary, and somewhere above the recommended intake is a point beyond which a nu-
trient is likely to become toxic. This point is known as the Tolerable Upper Intake
Level (UL). It is naive—and inaccurate—to think of recommendations as minimum
amounts. A more accurate view is to see a person’s nutrient needs as falling within a
range, with marginal and danger zones both below and above it (see Figure 1-6).
Paying attention to upper levels is particularly useful in guarding against the
overconsumption of nutrients, which may occur when people use large-dose supple-
ments and fortified foods regularly. Later chapters discuss the dangers associated
with excessively high intakes of vitamins and minerals, and the inside front cover
(page C) presents tables that include the upper-level values for selected nutrients.
Establishing Energy Recommendations
In contrast to the RDA and AI values for nutrients, the recommendation for energy
is not generous. Excess energy cannot be readily excreted and is eventually stored as
body fat. These reserves may be beneficial when food is scarce, but they can also
lead to obesity and its associated health consequences.
Estimated Energy Requirement (EER) The energy recommendation—called the
Estimated Energy Requirement (EER)—represents the average dietary energy in-
take (kcalories per day) that will maintain energy balance in a person who has a
healthy body weight and level of physical activity. ◆ Balance is key to the energy rec-
ommendation. Enough energy is needed to sustain a healthy and active life, but too
much energy can lead to weight gain and obesity. Because any amount in excess of en-
ergy needs will result in weight gain, no upper level for energy has been determined.
Acceptable Macronutrient Distribution Ranges (AMDR) People don’t eat
energy directly; they derive energy from foods containing carbohydrate, fat, and
protein. Each of these three energy-yielding nutrients contributes to the total energy
intake, and those contributions vary in relation to each other. The DRI Committee
has determined that the composition of a diet that provides adequate energy and
nutrients and reduces the risk of chronic diseases is:
• 45–65 percent kcalories from carbohydrate
• 20–35 percent kcalories from fat
• 10–35 percent kcalories from protein
These values are known as Acceptable Macronutrient Distribution Ranges
(AMDR).
Using Nutrient Recommendations
Although the intent of nutrient recommendations seems simple, they are the subject
of much misunderstanding and controversy. Perhaps the following facts will help
put them in perspective:
Safety
Danger
Inaccurate
view
Intake
RDA
Danger
of
toxicity
Marginal
Marginal
Danger
of
deficiency
Safety
Accurate
view
RDA or AI
Tolerable
Upper Intake
Level
Estimated
Average
Requirement
FIGURE 1-6 Inaccurate versus
Accurate View of Nutrient Intakes
The RDA or AI for a given nutrient
represents a point that lies within a range
of appropriate and reasonable intakes
between toxicity and deficiency. Both of
these recommendations are high enough
to provide reserves in times of short-term
dietary inadequacies, but not so high as
to approach toxicity. Nutrient intakes
above or below this range may be
equally harmful.
◆ Reference adults:
• Men: 19–30 yr, 5 ft 10 in., and 154 lb
• Women: 19–30 yr, 5 ft 4 in., and 126 lb
Tolerable Upper Intake Level (UL): the
maximum daily amount of a nutrient that
appears safe for most healthy people and
beyond which there is an increased risk of
adverse health effects.
Estimated Energy Requirement (EER):
the average dietary energy intake that
maintains energy balance and good health
in a person of a given age, gender, weight,
height, and level of physical activity.
Acceptable Macronutrient Distribution
Ranges (AMDR): ranges of intakes for the
energy nutrients that provide adequate
energy and nutrients and reduce the risk of
chronic diseases.

1. Estimates of adequate energy and nutrient intakes apply to healthy people. They
need to be adjusted for malnourished people or those with medical problems
who may require supplemented or restricted intakes.
2. Recommendations are not minimum requirements, nor are they necessarily opti-
mal intakes for all individuals. Recommendations can only target “most” of the
people and cannot account for individual variations in nutrient needs—yet.
Given the recent explosion of knowledge about genetics, the day may be fast
approaching when nutrition scientists will be able to determine an individual’s
optimal nutrient needs.9 Until then, registered dietitians ◆ and other qualified
health professionals can help determine if recommendations should be ad-
justed to meet individual needs.
3. Most nutrient goals are intended to be met through diets composed of a variety
of foods whenever possible. Because foods contain mixtures of nutrients and
nonnutrients, they deliver more than just those nutrients covered by the rec-
ommendations. Excess intakes of vitamins and minerals are unlikely when they
come from foods rather than supplements.
4. Recommendations apply to average daily intakes. Trying to meet the recommen-
dations for every nutrient every day is difficult and unnecessary. The length of
time over which a person’s intake can deviate from the average without risk of
deficiency or overdose varies for each nutrient, depending on how the body
uses and stores the nutrient. For most nutrients (such as thiamin and vitamin
C), deprivation would lead to rapid development of deficiency symptoms
(within days or weeks); for others (such as vitamin A and vitamin B12), deficien-
cies would develop more slowly (over months or years).
5. Each of the DRI categories serves a unique purpose. For example, the Estimated
Average Requirements are most appropriately used to develop and evaluate nu-
trition programs for groups such as schoolchildren or military personnel. The
RDA (or AI if an RDA is not available) can be used to set goals for individuals.
Tolerable Upper Intake Levels serve as a reminder to keep nutrient intakes be-
low amounts that increase the risk of toxicity—not a common problem when
nutrients derive from foods, but a real possibility for some nutrients if supple-
ments are used regularly.
With these understandings, professionals can use the DRI for a variety of purposes.
Comparing Nutrient Recommendations
At least 40 different nations and international organizations have published nutri-
ent standards similar to those used in the United States and Canada. Slight differ-
ences may be apparent, reflecting differences both in the interpretation of the data
from which the standards were derived and in the food habits and physical activi-
ties of the populations they serve.
Many countries use the recommendations developed by two international
groups: FAO (Food and Agriculture Organization) and WHO (World Health Orga-
nization). ◆ The FAO/WHO recommendations are considered sufficient to main-
tain health in nearly all healthy people worldwide.
◆ A registered dietitian is a college-
educated food and nutrition specialist who is
qualified to evaluate people’s nutritional
health and needs. See Highlight 1 for more
on what constitutes a nutrition expert.
◆ Nutrient recommendations from FAO/WHO
are provided in Appendix I.
The Dietary Reference Intakes (DRI) are a set of nutrient intake values that
can be used to plan and evaluate diets for healthy people. The Estimated Av-
erage Requirement (EAR) defines the amount of a nutrient that supports a spe-
cific function in the body for half of the population. The Recommended
Dietary Allowance (RDA) is based on the Estimated Average Requirement and
establishes a goal for dietary intake that will meet the needs of almost all
IN SUMMARY

20 • CHAPTER 1
Nutrition Assessment
What happens when a person doesn’t get enough or gets too much of a nutrient or
energy? If the deficiency or excess is significant over time, the person exhibits signs
of malnutrition. With a deficiency of energy, the person may display the symptoms
of undernutrition by becoming extremely thin, losing muscle tissue, and becoming
prone to infection and disease. With a deficiency of a nutrient, the person may expe-
rience skin rashes, depression, hair loss, bleeding gums, muscle spasms, night blind-
ness, or other symptoms. With an excess of energy, the person may become obese and
vulnerable to diseases associated with overnutrition such as heart disease and dia-
betes. With a sudden nutrient overdose, the person may experience
hot flashes, yellowing skin, a rapid heart rate, low blood pressure, or
other symptoms. Similarly, over time, regular intakes in excess of
needs may also have adverse effects.
Malnutrition symptoms—such as diarrhea, skin rashes, and fa-
tigue—are easy to miss because they resemble the symptoms of
other diseases. But a person who has learned how to use assess-
ment techniques to detect malnutrition can identify when these
conditions are caused by poor nutrition and can recommend steps
to correct it. This discussion presents the basics of nutrition assess-
ment; many more details are offered in Chapter 17 and in Appen-
dix E.
Nutrition Assessment of Individuals
To prepare a nutrition assessment, a registered dietitian or other
trained health care professional uses:
• Historical information
• Anthropometric data
• Physical examinations
• Laboratory tests
Each of these methods involves collecting data in various ways and interpreting
each finding in relation to the others to create a total picture.
Historical Information One step in evaluating nutrition status is to obtain infor-
mation about a person’s history with respect to health status, socioeconomic status,
drug use, and diet. The health history reflects a person’s medical record and may re-
veal a disease that interferes with the person’s ability to eat or the body’s use of nutri-
ents. The person’s family history of major diseases is also noteworthy, especially for
conditions such as heart disease that have a genetic tendency to run in families. Eco-
nomic circumstances may show a financial inability to buy foods or inadequate
kitchen facilities in which to prepare them. Social factors such as marital status, eth-
nic background, and educational level also influence food choices and nutrition sta-
tus. A drug history, including all prescribed and over-the-counter medications as well
as illegal substances, may highlight possible interactions that lead to nutrient defi-
ciencies (as described in Chapter 19). A diet history that examines a person’s intake of
healthy people. An Adequate Intake (AI) serves a similar purpose when an
RDA cannot be determined. The Estimated Energy Requirement (EER) defines
the average amount of energy intake needed to maintain energy balance, and
the Acceptable Macronutrient Distribution Ranges (AMDR) define the propor-
tions contributed by carbohydrate, fat, and protein to a healthy diet. The Tol-
erable Upper Intake Level (UL) establishes the highest amount that appears
safe for regular consumption.
A peek inside the mouth provides clues to a
person’s nutrition status. An inflamed tongue
may indicate a B vitamin deficiency, and mot-
tled teeth may reveal fluoride toxicity, for
example.
malnutrition: any condition caused by
excess or deficient food energy or nutrient
intake or by an imbalance of nutrients.
• mal = bad
undernutrition: deficient energy or
nutrients.
overnutrition: excess energy or nutrients.
nutrition assessment: a comprehensive
analysis of a person’s nutrition status that
uses health, socioeconomic, drug, and diet
histories; anthropometric measurements;
physical examinations; and laboratory tests.
©
Tom

Dee
Ann
McCarthy/CORBIS

foods, beverages, and supple-
ments may reveal either a sur-
plus or inadequacy of nutrients
or energy.
To take a diet history, the as-
sessor collects data about the
foods a person eats. The data
may be collected by recording
the foods the person has eaten
over a period of 24 hours, three
days, or a week or more or by
asking what foods the person
typically eats and how much of
each. The days in the record
must be fairly typical of the per-
son’s diet, and portion sizes
must be recorded accurately. To
determine the amounts of nutri-
ents consumed, the assessor usu-
ally enters the foods and their
portion sizes into a computer us-
ing a diet analysis program.
This step can also be done man-
ually by looking up each food in
a table of food composition such
as Appendix H in this book. The assessor then compares the calculated nutrient in-
takes with the DRI to determine the probability of adequacy (see Figure 1-7).10 Al-
ternatively, the diet history might be compared against standards such as the
USDA Food Guide or Dietary Guidelines (described in Chapter 2).
An estimate of energy and nutrient intakes from a diet history, when combined
with other sources of information, can help confirm or rule out the possibility of sus-
pected nutrition problems. A sufficient intake of a nutrient does not guarantee ad-
equacy, and an insufficient intake does not always indicate a deficiency. Such
findings, however, warn of possible problems.
Anthropometric Data A second technique that may help to reveal nutrition
problems is taking anthropometric measures such as height and weight. The as-
sessor compares a person’s measurements with standards specific for gender and
age or with previous measures on the same individual. (Chapter 8 presents informa-
tion on body weight and its standards.)
Measurements taken periodically and compared with previous measurements
reveal patterns and indicate trends in a person’s overall nutrition status, but they
provide little information about specific nutrients. Instead, measurements out of
line with expectations may reveal such problems as growth failure in children,
wasting or swelling of body tissues in adults, and obesity—conditions that may re-
flect energy or nutrient deficiencies or excesses.
Physical Examinations A third nutrition assessment technique is a physical exam-
ination looking for clues to poor nutrition status. Every part of the body that can be in-
spected may offer such clues: the hair, eyes, skin, posture, tongue, fingernails, and
others. The examination requires skill because many physical signs reflect more than
one nutrient deficiency or toxicity—or even nonnutrition conditions. Like the other as-
sessment techniques, a physical examination alone does not yield firm conclusions.
Instead, physical examinations reveal possible imbalances that must be confirmed by
other assessment techniques, or they confirm results from other assessment measures.
Laboratory Tests A fourth way to detect a developing deficiency, imbalance, or
toxicity is to take samples of blood or urine, analyze them in the laboratory, and
compare the results with normal values for a similar population. ◆ A goal of nutrition
EAR
RDA
Usual
intake
of
nutrient
X
(units/day)
Intake
probably
inadequate
Intake
possibly
inadequate
High Intake
probably
adequate
Low
If a person’s usual intake falls above
the RDA, the intake is probably
adequate because the RDA covers
the needs of almost all people.
A usual intake that falls between the
RDA and the EAR is more difficult to
assess; the intake may be adequate,
but the chances are greater or equal
that it is inadequate.
If the usual intake falls below the
EAR, it is probably inadequate.
FIGURE 1-7 Using the DRI to Assess the Dietary Intake of a Healthy Individual
anthropometric (AN-throw-poe-MET-rick):
relating to measurement of the physical
characteristics of the body, such as height
and weight.
• anthropos = human
• metric = measuring
◆ Assessment may one day depend on
measures of how a nutrient influences
genetic activity within the cells, instead of
quantities in the blood or other tissues.

assessment is to uncover early signs of malnutrition be-
fore symptoms appear, and laboratory tests are most use-
ful for this purpose. In addition, they can confirm
suspicions raised by other assessment methods.
Iron, for Example The mineral iron can be used to il-
lustrate the stages in the development of a nutrient defi-
ciency and the assessment techniques useful in detecting
them. The overt, or outward, signs of an iron deficiency
appear at the end of a long sequence of events. Figure
1-8 describes what happens in the body as a nutrient de-
ficiency progresses and shows which assessment meth-
ods can reveal those changes.
First, the body has too little iron—either because iron
is lacking in the person’s diet (a primary deficiency)
or because the person’s body doesn’t absorb enough,
excretes too much, or uses iron inefficiently (a second-
ary deficiency). A diet history provides clues to pri-
mary deficiencies; a health history provides clues to
secondary deficiencies.
Next, the body begins to use up its stores of iron. At
this stage, the deficiency might be described as sub-
clinical. It exists as a covert condition, and although
it might be detected by laboratory tests, no outward
signs are apparent.
Finally, the body’s iron stores are exhausted. Now, it
cannot make enough iron-containing red blood cells to
replace those that are aging and dying. Iron is needed
in red blood cells to carry oxygen to all the body’s tis-
sues. When iron is lacking, fewer red blood cells are made, the new ones are pale
and small, and every part of the body feels the effects of oxygen shortage. Now the
overt symptoms of deficiency appear—weakness, fatigue, pallor, and headaches,
reflecting the iron-deficient state of the blood. A physical examination will reveal
these symptoms.
Nutrition Assessment of Populations
To assess a population’s nutrition status, researchers conduct surveys using techniques
similar to those used on individuals. The data collected are then used by various agen-
cies for numerous purposes, including the development of national health goals.
National Nutrition Surveys The National Nutrition Monitoring program coor-
dinates the many nutrition-related surveys and research activities of various federal
agencies. The integration of two major national surveys ◆ provides comprehensive
data efficiently.11 One survey collects data on the kinds and amounts of foods peo-
ple eat.* Then researchers calculate the energy and nutrients in the foods and com-
pare the amounts consumed with a standard. The other survey examines the people
themselves, using anthropometric measurements, physical examinations, and lab-
oratory tests.†12 The data provide valuable information on several nutrition-related
conditions, such as growth retardation, heart disease, and nutrient deficiencies. Na-
tional nutrition surveys often oversample high-risk groups (low-income families,
pregnant women, adolescents, the elderly, African Americans, and Mexican Ameri-
cans) to glean an accurate estimate of their health and nutrition status.
The resulting wealth of information from the national nutrition surveys is used
for a variety of purposes. For example, Congress uses this information to establish
WHAT HAPPENS IN
THE BODY
WHICH ASSESSMENT
METHODS REVEAL CHANGES
Primary deficiency caused by
inadequate diet
or
Secondary deficiency caused
by problem inside the body
Diet history
Health history
Laboratory tests
Physical examination and
anthropometric measures
Declining nutrient stores
(subclinical)
and
Abnormal functions inside the body
(covert)
Physical (overt) signs
and symptoms
FIGURE 1-8 Stages in the Development of a Nutrient
Deficiency
Internal changes precede outward signs of deficiencies. However,
outward signs of sickness need not appear before a person takes
corrective measures. Laboratory tests can help determine nutrient
status in the early stages.
◆ The new integrated survey is called What We
Eat in America.
overt (oh-VERT): out in the open and easy to
observe.
• ouvrir = to open
primary deficiency: a nutrient deficiency
caused by inadequate dietary intake of a
nutrient.
secondary deficiency: a nutrient deficiency
caused by something other than an
inadequate intake such as a disease
condition or drug interaction that reduces
absorption, accelerates use, hastens
excretion, or destroys the nutrient.
subclinical deficiency: a deficiency in the
early stages, before the outward signs have
appeared.
covert (KOH-vert): hidden, as if under covers.
• couvrir = to cover
* This survey was formerly called the Continuing Survey of Food Intakes by Individuals (CSFII), con-
ducted by the U.S. Department of Agriculture (USDA).
† This survey is known as the National Health and Nutrition Examination Survey (NHANES), conducted
by the U.S. Department of Health and Human Services (DHHS).
22 • CHAPTER 1

public policy on nutrition education, food assistance programs, and the regulation
of the food supply. Scientists use the information to establish research priorities.
The food industry uses these data to guide decisions in public relations and product
development.13 The Dietary Reference Intakes and other major reports that exam-
ine the relationships between diet and health depend on information collected
from these nutrition surveys. These data also provide the basis for developing and
monitoring national health goals.
National Health Goals Healthy People is a program that identifies the nation’s
health priorities and guides policies that promote health and prevent disease. At the
start of each decade, the program sets goals for improving the nation’s health during
the following ten years. The goals of Healthy People 2010 focus on “improving the
quality of life and eliminating disparity in health among racial and ethnic groups.”14
Nutrition is one of many focus areas, each with numerous objectives. Table 1-4 lists
the nutrition and overweight objectives for 2010, and Appendix J includes a table of
nutrition-related objectives from other focus areas.
At mid-decade, the nation’s progress toward meeting its nutrition and over-
weight Healthy People 2010 goals was somewhat bleak. Trends in overweight and
obesity worsened. Objectives to eat more fruits, vegetables, and whole grains and
to increase physical activity showed little or no improvement. Clearly, “what we
eat in America” must change if we hope to meet the Healthy People 2010 goals.
National Trends What do we eat in America and how has it changed over the
past 30 years?15 The short answer to both questions is “a lot.” We eat more meals
away from home, particularly at fast-food restaurants. We eat larger portions. We
drink more sweetened beverages and eat more energy-dense, nutrient-poor foods
such as candy and chips. We snack frequently. As a result of these dietary habits, our
energy intake has risen and, consequently, so has the incidence of overweight and
obesity. Overweight and obesity, in turn, profoundly influence our health—as the
next section explains.
Surveys provide valuable information about
the kinds of foods people eat.
TABLE 1-4 Healthy People 2010 Nutrition and Overweight Objectives
• Increase the proportion of adults who are at
a healthy weight.
• Reduce the proportion of adults who are
obese.
• Reduce the proportion of children and
adolescents who are overweight or obese.
• Reduce growth retardation among low-
income children under age 5 years.
• Increase the proportion of persons aged 2
years and older who consume at least two
daily servings of fruit.
years and older who consume at least three
daily servings of vegetables, with at least
one-third being dark green or orange
vegetables.
years and older who consume at least six
daily servings of grain products, with at least
three being whole grains.
years and older who consume less than 10
percent of kcalories from saturated fat.
years and older who consume no more than
30 percent of kcalories from total fat.
years and older who consume 2400 mg or
less of sodium.
years and older who meet dietary recommen-
dations for calcium.
• Reduce iron deficiency among young children,
females of childbearing age, and pregnant
females.
• Reduce anemia among low-income pregnant
females in their third trimester.
• Increase the proportion of children and
adolescents aged 6 to 19 years whose intake
of meals and snacks at school contributes to
good overall dietary quality.
• Increase the proportion of worksites that offer
nutrition or weight management classes or
counseling.
• Increase the proportion of physician office
visits made by patients with a diagnosis of
cardiovascular disease, diabetes, or hyper-
lipidemia that include counseling or education
related to diet and nutrition.
• Increase food security among U.S. households
and in so doing reduce hunger.
NOTE: “Nutrition and Overweight” is one of 28 focus areas, each with numerous objectives. Several of the other focus areas
have nutrition-related objectives, and these are presented in Appendix J.
SOURCE: Healthy People 2010, www.healthypeople.gov
Healthy People: a national public health
initiative under the jurisdiction of the U.S.
Department of Health and Human Services
(DHHS) that identifies the most significant
preventable threats to health and focuses
efforts toward eliminating them.
Jesco
Tscholitsch/Getty
Images

TABLE 1-5 Leading Causes of Death
in the United States
24 • CHAPTER 1
Diet and Health
Diet has always played a vital role in supporting health. Early nutrition research fo-
cused on identifying the nutrients in foods that would prevent such common dis-
eases as rickets and scurvy, the vitamin D– and vitamin C–deficiency diseases. With
this knowledge, developed countries have successfully defended against nutrient de-
ficiency diseases. World hunger and nutrient deficiency diseases still pose a major
health threat in developing countries, however, but not because of a lack of nutri-
tion knowledge. More recently, nutrition research has focused on chronic diseases
associated with energy and nutrient excesses. Once thought to be “rich countries’
problems,” chronic diseases have now become epidemic in developing countries as
well—contributing to three out of five deaths worldwide.16
Chronic Diseases
Table 1-5 lists the ten leading causes of death in the United States. These “causes”
are stated as if a single condition such as heart disease caused death, but most
chronic diseases arise from multiple factors over many years. A person who died
of heart disease may have been overweight, had high blood pressure, been a cig-
arette smoker, and spent years eating a diet high in saturated fat and getting too
little exercise.
Of course, not all people who die of heart disease fit this description, nor do all
people with these characteristics die of heart disease. People who are overweight
might die from the complications of diabetes instead, or those who smoke might
die of cancer. They might even die from something totally unrelated to any of
these factors, such as an automobile accident. Still, statistical studies have shown
that certain conditions and behaviors are linked to certain diseases.
Notice that Table 1-5 highlights five of the top six causes of death as having a
link with diet or alcohol. During the past 30 years, as knowledge about these diet
and disease relationships grew, the death rates for four of these—heart disease, can-
cers, strokes, and accidents—decreased.17 Death rates for diabetes—a chronic dis-
ease closely associated with obesity—increased.
Risk Factors for Chronic Diseases
Factors that increase or reduce the risk of developing chronic diseases can be identi-
fied by analyzing statistical data. A strong association between a risk factor and a
disease means that when the factor is present, the likelihood of developing the dis-
ease increases. It does not mean that all people with the risk factor will develop the
disease. Similarly, a lack of risk factors does not guarantee freedom from a given dis-
ease. On the average, though, the more risk factors in a person’s life, the greater that
person’s chances of developing the disease. Conversely, the fewer risk factors in a
person’s life, the better the chances for good health.
People become malnourished when they get too little or too much energy or
nutrients. Deficiencies, excesses, and imbalances of nutrients lead to malnu-
trition diseases. To detect malnutrition in individuals, health care profession-
als use four nutrition assessment methods. Reviewing dietary data and health
information may suggest a nutrition problem in its earliest stages. Laboratory
tests may detect it before it becomes overt, whereas anthropometrics and phys-
ical examinations pick up on the problem only after it causes symptoms. Na-
tional surveys use similar assessment methods to measure people’s food
consumption and to evaluate the nutrition status of populations.
IN SUMMARY
Percentage of
Total Deaths
1. Heart disease 28.0
2. Cancers 22.7
3. Strokes 6.4
4. Chronic lung diseases 5.2
5. Accidents 4.5
6. Diabetes mellitus 3.0
7. Pneumonia and influenza 2.7
8. Alzheimer’s disease 2.6
9. Kidney diseases 1.7
10. Blood infections 1.4
NOTE: The diseases highlighted in green have relationships
with diet; yellow indicates a relationship with alcohol.
SOURCE: National Center for Health Statistics:
www.cdc.gov/nchs
chronic diseases: diseases characterized by
a slow progression and long duration.
Examples include heart disease, cancer,
and diabetes.
risk factor: a condition or behavior
associated with an elevated frequency of a
disease but not proved to be causal. Leading
risk factors for chronic diseases include
obesity, cigarette smoking, high blood
pressure, high blood cholesterol, physical
inactivity, and a diet high in saturated fats
and low in vegetables, fruits, and whole
grains.

Risk Factors Persist Risk factors tend to persist over time. Without interven-
tion, a young adult with high blood pressure will most likely continue to have
high blood pressure as an older adult, for example. Thus, to minimize the dam-
age, early intervention is most effective.
Risk Factors Cluster Risk factors tend to cluster. For example, a person who is
obese may be physically inactive, have high blood pressure, and have high blood
cholesterol—all risk factors associated with heart disease. Intervention that focuses
on one risk factor often benefits the others as well. For example, physical activity can
help reduce weight. The physical activity and weight loss will, in turn, help to lower
blood pressure and blood cholesterol.
Risk Factors in Perspective The most prominent factor contributing to death in
the United States is tobacco use, ◆ followed closely by diet and activity patterns, and
then alcohol use (see Table 1-6).18 Risk factors such as smoking, poor dietary habits,
physical inactivity, and alcohol consumption are personal behaviors that can be
changed. Decisions to not smoke, to eat a well-balanced diet, to engage in regular
physical activity, and to drink alcohol in moderation (if at all) improve the likeli-
hood that a person will enjoy good health. Other risk factors, such as genetics, gen-
der, and age, also play important roles in the development of chronic diseases, but
they cannot be changed. Health recommendations acknowledge the influence of
such factors on the development of disease, but they must focus on the factors that
are changeable. For the two out of three Americans who do not smoke or drink al-
cohol excessively, the one choice that can influence long-term health prospects more
than any other is diet.
Factors Percentage of Deaths
Tobacco 18
Poor diet/inactivity 15
Alcohol 4
Microbial agents 3
Toxic agents 2
Motor vehicles 2
Firearms 1
Sexual behavior 1
Illicit drugs 1
SOURCE: A. H. Mokdad and coauthors, Actual causes of death
in the United States, 2000, Journal of the American Medical
Association 291 (2004): 1238–1245, with corrections from
Journal of the American Medical Association 293 (2005): 298.
TABLE 1-6 Factors Contributing to
Deaths in the United States
◆ Cigarette smoking is responsible for almost
one of every five deaths each year.
Physical activity can be both fun and beneficial.
Within the range set by genetics, a person’s choice of diet influences long-term
health. Diet has no influence on some diseases but is linked closely to others.
Personal life choices, such as engaging in physical activity and using tobacco
or alcohol, also affect health for the better or worse.
IN SUMMARY
©
PhotoDisc/Getty
Images

26 • CHAPTER 1
The next several chapters provide many more details about nutrients and how they
support health. Whenever appropriate, the discussion shows how diet influences
each of today’s major diseases. Dietary recommendations appear again and again,
as each nutrient’s relationships with health is explored. Most people who follow the
recommendations will benefit and can enjoy good health into their later years.
Each chapter in this book ends with simple Nutrition Portfolio activities that invite you
to review key messages and consider whether your personal choices are meeting the
dietary goals introduced in the text. By keeping a journal of these Nutrition Portfolio
assignments, you can examine how your knowledge and behaviors change as you
progress in your study of nutrition.
Your food choices play a key role in keeping you healthy and reducing your risk of
chronic diseases.
■ Identify the factors that most influence your food choices for meals and snacks.
■ List the chronic disease risk factors and conditions (listed in the definition of risk
factors on p. 24) that you or members of your family have.
■ Describe lifestyle changes you can make to improve your chances of enjoying
good health.
Nutrition Portfolio
For further study of topics covered in this chapter, log on to academic.cengage
.com/nutrition/rolfes/UNCN8e. Go to Chapter 1, then to Nutrition on the Net.
• Search for “nutrition” at the U.S. Government health and
nutrition information sites: www.healthfinder.gov or
www.nutrition.gov
• Learn more about basic science research from the National
Science Foundation and Research!America: www.nsf.gov
and researchamerica.org
• Review the Dietary Reference Intakes: www.nap.edu
• Review nutrition recommendations from the Food and
Agriculture Organization and the World Health Organiza-
tion: www.fao.org and www.who.org
• View Healthy People 2010: www.healthypeople.gov
• Visit the Food and Nutrition section of the Healthy Living
area in Health Canada: www.hc-sc.gc.ca
• Learn about the national nutrition survey:
www.cdc.gov/nchs/nhanes.htm
• Get information from the Food Surveys Research Group:
www.barc.usda.gov/bhnrc/foodsurvey
• Visit the food and nutrition center of the Mayo Clinic:
www.mayohealth.org
• Create a chart of your family health history at the U.S.
Surgeon General’s site: familyhistory.hhs.gov

Several chapters end with problems to give you practice in
doing simple nutrition-related calculations. Although the
situations are hypothetical, the numbers are real, and calcu-
lating the answers (check them on p. 29) provides a valuable
nutrition lesson. Once you have mastered these examples,
you will be prepared to examine your own food choices. Be
sure to show your calculations for each problem.
1. Calculate the energy provided by a food’s energy-nutrient
contents. A cup of fried rice contains 5 grams protein, 30
grams carbohydrate, and 11 grams fat.
a. How many kcalories does the rice provide from
these energy nutrients?
kcal protein
kcal carbohydrate
kcal fat
Total kcal
b. What percentage of the energy in the fried rice
comes from each of the energy-yielding nutrients?
% kcal from protein
% kcal from carbohydrate
% kcal from fat
Total %
Note: The total should add up to 100%; 99% or
101% due to rounding is also acceptable.
c. Calculate how many of the 146 kcalories provided
by a 12-ounce can of beer come from alcohol, if
the beer contains 1 gram protein and 13 grams
carbohydrate. (Note: The remaining kcalories de-
rive from alcohol.)
1 g protein kcal protein
13 g carbohydrate kcal carbohydrate
kcal alcohol
How many grams of alcohol does this represent?
g alcohol
2. Even a little nutrition knowledge can help you identify
some bogus claims. Consider an advertisement for a new
“super supplement” that claims the product provides 15
grams protein and 10 kcalories per dose. Is this possible?
Why or why not? kcal
To assess your understanding of chapter topics, take the Student Practice Test
and explore the modules recommended in your Personalized Study Plan.
Log on to academic.cengage.com/login.
These questions will help you review this chapter. You will
find the answers in the discussions on the pages provided.
1. Give several reasons (and examples) why people make
the food choices that they do. (pp. 3–5)
2. What is a nutrient? Name the six classes of nutrients
found in foods. What is an essential nutrient? (pp. 6–7)
3. Which nutrients are inorganic, and which are organic?
Discuss the significance of that distinction. (pp. 7, 10)
4. Which nutrients yield energy, and how much energy do
they yield per gram? How is energy measured? (pp. 7–10)
5. Describe how alcohol resembles nutrients. Why is alco-
hol not considered a nutrient? (pp. 8, 10)
6. What is the science of nutrition? Describe the types of
research studies and methods used in acquiring nutrition
information. (pp. 11–16)
7. Explain how variables might be correlational but not
causal. (p. 15)
8. What are the DRI? Who develops the DRI? To whom do
they apply? How are they used? In your description,
identify the categories of DRI and indicate how they are
related. (pp. 16–19)
9. What judgment factors are involved in setting the en-
ergy and nutrient recommendations? (pp. 17–18)
10. What happens when people get either too little or too
much energy or nutrients? Define malnutrition, under-
nutrition, and overnutrition. Describe the four methods
used to detect energy and nutrient deficiencies and ex-
cesses. (pp. 20–22)
11. What methods are used in nutrition surveys? What
kinds of information can these surveys provide?
(pp. 22–23)
12. Describe risk factors and their relationships to disease.
(pp. 24–25)
These multiple choice questions will help you prepare for an
exam. Answers can be found on p. 29.
1. When people eat the foods typical of their families or
geographic region, their choices are influenced by:
a. habit.
b. nutrition.
c. personal preference.
d. ethnic heritage or tradition.
2. Both the human body and many foods are composed
mostly of:
a. fat.
b. water.
c. minerals.
d. proteins.
STUDY QUESTIONS
For additional practice, log on to academic.cengage.com/login. Go to Chapter 1, then to Nutrition Calculations.

28 • CHAPTER 1
3. The inorganic nutrients are:
a. proteins and fats.
b. vitamins and minerals.
c. minerals and water.
d. vitamins and proteins.
4. The energy-yielding nutrients are:
a. fats, minerals, and water.
b. minerals, proteins, and vitamins.
c. carbohydrates, fats, and vitamins.
d. carbohydrates, fats, and proteins.
5. Studies of populations that reveal correlations between
dietary habits and disease incidence are:
a. clinical trials.
b. laboratory studies.
c. case-control studies.
d. epidemiological studies.
6. An experiment in which neither the researchers nor the
subjects know who is receiving the treatment is known as:
a. double blind.
b. double control.
c. blind variable.
d. placebo control.
7. An RDA represents the:
a. highest amount of a nutrient that appears safe for
most healthy people.
b. lowest amount of a nutrient that will maintain a
specified criterion of adequacy.
c. average amount of a nutrient considered adequate
to meet the known nutrient needs of practically all
healthy people.
d. average amount of a nutrient that will maintain a
specific biochemical or physiological function in
half the people.
8. Historical information, physical examinations, laboratory
tests, and anthropometric measures are:
a. techniques used in diet planning.
b. steps used in the scientific method.
c. approaches used in disease prevention.
d. methods used in a nutrition assessment.
9. A deficiency caused by an inadequate dietary intake is a(n):
a. overt deficiency.
b. covert deficiency.
c. primary deficiency.
d. secondary deficiency.
10. Behaviors such as smoking, dietary habits, physical activ-
ity, and alcohol consumption that influence the develop-
ment of disease are known as:
a. risk factors.
b. chronic causes.
c. preventive agents.
d. disease descriptors.
1. J. A. Mennella, M. Y. Pepino, and D. R.
Reed, Genetic and environmental determi-
nants of bitter perception and sweet prefer-
ences, Pediatrics 115 (2005): e216.
2. J. E. Tillotson, Our ready-prepared, ready-to-
eat nation, Nutrition Today 37 (2002):
36–38.
3. D. Benton, Role of parents in the determi-
nation of the food preferences of children
and the development of obesity, Interna-
tional Journal of Obesity Related Metabolic
Disorders 28 (2004): 858–869.
4. L. Canetti, E. Bachar, and E. M. Berry, Food
and emotion, Behavioural Processes 60
(2002): 157–164.
5. Position of the American Dietetic Associa-
tion: Functional foods, Journal of the Ameri-
can Dietetic Association 104 (2004): 814–826.
tion: Total diet approach to communicating
food and nutrition information, Journal of
the American Dietetic Association 102 (2002):
100–108.
7. L. Afman and M. Müller, Nutrigenomics:
From molecular nutrition to prevention of
disease, Journal of the American Dietetic
Association 106 (2006): 569–576; J. Ordovas
and V. Mooser, Nutrigenomics and nutrige-
netics, Current Opinion in Lipidology 15
(2005): 101–108; D. Shattuck, Nutritional
genomics, Journal of the American Dietetic
Association 103 (2003): 16, 18; P. Trayhurn,
Nutritional genomics—”Nutrigenomics,”
British Journal of Nutrition 89 (2003): 1–2.
8. Committee on Dietary Reference Intakes,
Dietary Reference Intakes for Water, Potassium,
Sodium, Chloride, and Sulfate (Washington,
D.C.: National Academies Press, 2005);
Committee on Dietary Reference Intakes,
Dietary Reference Intakes for Energy, Carbohy-
drate, Fiber, Fat, Fatty Acids, Cholesterol,
Protein, and Amino Acids (Washington, D.C.:
National Academies Press, 2005); Commit-
tee on Dietary Reference Intakes, Dietary
Reference Intakes for Vitamin A, Vitamin K,
Arsenic, Boron, Chromium, Copper, Iodine,
Iron, Manganese, Molybdenum, Nickel, Silicon,
Vanadium, and Zinc (Washington, D.C.:
National Academy Press, 2001); Committee
on Dietary Reference Intakes, Dietary Refer-
ence Intakes for Vitamin C, Vitamin E, Sele-
nium, and Carotenoids (Washington, D.C.:
ence Intakes for Thiamin, Riboflavin, Niacin,
Vitamin B6, Folate, Vitamin B12, Pantothenic
Acid, Biotin, and Choline (Washington, D.C.:
ence Intakes for Calcium, Phosphorus, Magne-
sium, Vitamin D, and Fluoride (Washington,
D.C.: National Academy Press, 1997).
9. Afman and Müller, 2006.
10. S. P. Murphy, S. I. Barr, and M. I. Poos,
Using the new Dietary Reference Intakes to
assess diets: A map to the maze, Nutrition
Reviews 60 (2002): 267–275.
11. J. Dwyer and coauthors, Integration of the
Continuing Survey of Food Intakes by
Individuals and the National Health and
Nutrition Examination Survey, Journal of the
American Dietetic Association 101 (2001):
1142–1143.
12. J. Dwyer and coauthors, Collection of food
and dietary supplement intake data: What
we eat in America—NHANES, Journal of
Nutrition 133 (2003): 590S–600S.
13. S. J. Crockett and coauthors, Nutrition
monitoring application in the food indus-
try, Nutrition Today 37 (2002): 130–135.
14. U.S. Department of Health and Human
Services, Healthy People 2010: Understanding
and Improving Health, January 2000.
15. R. R. Briefel and C. L. Johnson, Secular
trends in dietary intake in the United States,
Annual Review of Nutrition 24 (2004):
401–431.
16. B. M. Popkin, Global nutrition dynamics:
The world is shifting rapidly toward a diet
linked with noncommunicable diseases,
American Journal of Clinical Nutrition 84
(2006): 289–298; D. Yach and coauthors,
The global burden of chronic diseases:
Overcoming impediments to prevention
and control, Journal of the American Medical
Association 291 (2004): 2616–2622.
17. A. Jemal and coauthors, Trends in the
leading causes of death in the United States,
1970–2002, Journal of the American Medical
Association 294 (2005): 1255–1259.
18. A. H. Mokdad and coauthors, Actual causes
of death in the United States, 2000, Journal
of the American Medical Association 291
(2004): 1238–1245.
REFERENCES

Nutrition Calculations
1. a. 5 g protein 4 kcal/g = 20 kcal protein
30 g carbohydrate 4 kcal/g = 120 kcal carbohydrate
11 g fat 9 kcal/g = 99 kcal fat
Total = 239 kcal
b. 20 kcal 239 kcal 100 = 8.4% kcal from protein
120 kcal 239 kcal 100 = 50.2% kcal from carbohydrate
99 kcal 239 kcal 100 = 41.4% kcal from fat
Total = 100%.
c. 1 g protein = 4 kcal protein
13 g carbohydrate = 52 kcal carbohydrate
146 total kcal 56 kcal (protein carbohydrate)
= 90 kcal alcohol
90 kcal alcohol 7 g/kcal = 12.9 g alcohol
2. No. 15 g protein 4 kcal/g = 60 kcal
Study Questions (multiple choice)
1. d 2. b 3. c 4. d 5. d 6. a 7. c 8. d
9. c 10. a
ANSWERS

HIGHLIGHT 1
30
How can people distinguish valid nutrition in-
formation from misinformation? One excellent
approach is to notice who is providing the in-
formation. The “who” behind the information
is not always evident, though, especially in the
world of electronic media. Keep in mind that
people develop CD-ROMs and create websites
on the Internet, just as people write books and
report the news. In all cases, consumers need to determine whether
the person is qualified to provide nutrition information.
This highlight begins by examining the unique potential as
well as the problems of relying on the Internet and the media for
nutrition information. It continues with a discussion of how to
identify reliable nutrition information that applies to all resources,
including the Internet and the news. (The glossary on p. 32 de-
fines related terms.)
Nutrition on the Net
Got a question? The Internet has an answer. The Internet offers
endless opportunities to obtain high-quality information, but it
also delivers an abundance of incomplete, misleading, or inaccu-
rate information.1 Simply put: anyone can publish anything.
With hundreds of millions of websites on the World Wide
Web, searching for nutrition information can be an overwhelming
experience—much like walking into an enormous bookstore with
millions of books, magazines, newspapers, and videos. And like a
bookstore, the Internet offers no guarantees of the accuracy of the
information found there—much of which is pure fiction.
When using the Internet, keep in mind that the quality of
health-related information available covers a broad range.2 You
must evaluate websites for their accuracy, just like every other
source. The accompanying “How to” provides tips for determin-
ing whether a website is reliable.
One of the most trustworthy sites used by scientists and others
is the National Library of Medicine’s PubMed, which provides free
access to over 10 million abstracts (short descriptions) of research
papers published in scientific journals around the world. Many
abstracts provide links to websites where full articles are available.
Figure H1-1 introduces this valuable resource.
Did you receive the e-mail warning about Costa Rican bananas
causing the disease “necrotizing fasciitis”? If so, you’ve been
scammed by Internet misinformation. When
nutrition information arrives in unsolicited e-
mails, be suspicious if:
• The person sending it to you didn’t write it
and you cannot determine who did or if
that person is a nutrition expert
• The phrase “Forward this to everyone you
know” appears
• The phrase “This is not a hoax” appears; chances are that it
is
• The news is sensational and you’ve never heard about it
from legitimate sources
• The language is emphatic and the text is sprinkled with
capitalized words and exclamation marks
• No references are given or, if present, are of questionable
validity when examined
• The message has been debunked on websites such as
www.quackwatch.org or www.urbanlegends.com
Nutrition in the News
Consumers get much of their nutrition information from televi-
sion news and magazine reports, which have heightened aware-
ness of how diet influences the development of diseases.
Consumers benefit from news coverage of nutrition when they
learn to make lifestyle changes that will improve their health.
Sometimes, however, when magazine articles or television pro-
grams report nutrition trends, they mislead consumers and create
confusion. They often tell a lopsided story based on a few testi-
monials instead of presenting the results of research studies or a
balance of expert opinions.
Tight deadlines and limited understanding sometimes make
it difficult to provide a thorough report. Hungry for the latest
news, the media often report scientific findings prematurely—
without benefit of careful interpretation, replication, and peer
review.3 Usually, the reports present findings from a single, re-
cently released study, making the news current and controver-
sial. Consequently, the public receives diet and health news
quickly, but not always in perspective. Reporters may twist in-
conclusive findings into “meaningful discoveries” when pres-
©
Laurent/Jessy/©
BSIP/Phototake
Nutrition Information and
Misinformation—On the Net
and in the News

sured to write catchy headlines and sensa-
tional stories.
As a result, “surprising new findings”
seem to contradict one another, and con-
sumers feel frustrated and betrayed. Occa-
sionally, the reports are downright false,
but more often the apparent contradic-
tions are simply the normal result of sci-
ence at work. A single study contributes to
the big picture, but when viewed alone, it
can easily distort the image. To be mean-
ingful, the conclusions of any study must
be presented cautiously within the context
of other research findings.
Identifying Nutrition
Experts
Regardless of whether the medium is elec-
tronic, print, or video, consumers need to
ask whether the person behind the informa-
tion is qualified to speak on nutrition. If the
creator of an Internet website recommends eating three pineapples
a day to lose weight, a trainer at the gym praises a high-protein
diet, or a health-store clerk suggests an herbal supplement, should
you believe these people? Can you distinguish between accurate
news reports and infomercials on television? Have you noticed that
many televised nutrition messages are presented by celebrities, fit-
ness experts, psychologists, food editors, and chefs—that is, almost
anyone except a dietitian? When you
are confused or need sound dietary ad-
vice, whom should you ask?
Physicians and Other Health
Care Professionals
Many people turn to physicians or other
health care professionals for dietary ad-
vice, expecting them to know about all
health-related matters. But are they the
best sources of accurate and current in-
formation on nutrition? Only about 30
percent of all medical schools in the
United States require students to take a
separate nutrition course; less than half
require the minimum 25 hours of nutri-
tion instruction recommended by the
National Academy of Sciences.4 By com-
parison, most students reading this text
are taking a nutrition class that provides
an average of 45 hours of instruction.
The American Dietetic Associa-
tion (ADA) asserts that standardized
nutrition education should be included
NUTRITION INFORMATION AND MISINFORMATION—ON THE NET AND IN THE NEWS • 31
To determine whether a website offers
reliable nutrition information, ask the
following questions:
• Who? Who is responsible for the site? Is
it staffed by qualified professionals? Look
for the authors’ names and credentials.
Have experts reviewed the content for
accuracy?
• When? When was the site last updated?
Because nutrition is an ever-changing
science, sites need to be dated and up-
dated frequently.
• Where? Where is the information com-
ing from? The three letters following the
dot in a Web address identify the site’s
affiliation. Addresses ending in “gov”
(government), “edu” (educational insti-
tute), and “org” (organization) generally
provide reliable information; “com”
(commercial) sites represent businesses
and, depending on their qualifications
and integrity, may or may not offer de-
pendable information.
• Why? Why is the site giving you this
information? Is the site providing a public
service or selling a product? Many com-
mercial sites provide accurate information,
but some do not. When money is the
prime motivation, be aware that the
information may be biased.
If you are satisfied with the answers to all
of the questions above, then ask this final
question:
• What? What is the message, and is it in
line with other reliable sources? Informa-
tion that contradicts common knowledge
should be questioned. Many reliable sites
provide links to other sites to facilitate
your quest for knowledge, but this provi-
sion alone does not guarantee a reputable
intention. Be aware that any site can link
to any other site without permission.
HOW TO Determine Whether a Website Is Reliable
About Entrez
Text Version
Entrez PubMed
Overview
Help/FAQ
Tutorial
New/Noteworthy
• Enter one or more search terms, or click Preview/Index for
advanced searching.
• Enter author names as smith jc. Initials are optional.
• Enter journal titles in full or as MEDLINE
abbreviations. Use the Journals Database to find journal titles.
Search
National
Library
of Medicine NLM
for
PubMed Go Clear
Limits Preview/Index History Clipboard Details
Refine the
search by
setting limits
Type search
terms here
Use tutorial
resources to
answer
questions
FIGURE H1-1 PUBMED (www.pubmed.gov): Internet Resource for Scientific
Nutrition References
The U.S. National Library of Medicine’s PubMed website offers tutorials to help teach
beginners to use the search system effectively. Often, simply visiting the site, typing a
query in the “Search for” box, and clicking “Go” will yield satisfactory results.
For example, to find research concerning calcium and bone health, typing “cal-
cium bone” nets over 30,000 results. Try setting limits on dates, types of articles, lan-
guages, and other criteria to obtain a more manageable number of abstracts to
peruse.
in the curricula for all health care professionals: physicians, nurses,
physician’s assistants, dental hygienists, physical and occupa-
tional therapists, social workers, and all others who provide ser-
vices directly to clients. When these professionals understand the
relevance of nutrition in the treatment and prevention of disease
and have command of reliable nutrition information, then all the
people they serve will also be better informed.

32 • Highlight 1
Most health care professionals appreciate the connections be-
tween health and nutrition. Those who have specialized in clinical nu-
trition are especially well qualified to speak on the subject. Few,
however, have the time or experience to develop diet plans and pro-
vide detailed diet instructions for clients. Often they wisely refer
clients to a qualified nutrition expert—a registered dietitian (RD).
Registered Dietitians (RD)
A registered dietitian (RD) has the educational background neces-
sary to deliver reliable nutrition advice and care.5 To become an
RD, a person must earn an undergraduate degree requiring about
60 semester hours in nutrition, food science, and other related
subjects; complete a year’s clinical internship or the equivalent;
pass a national examination administered by the ADA; and main-
tain up-to-date knowledge and registration by participating in
required continuing education activities such as attending semi-
nars, taking courses, or writing professional papers.
Some states allow anyone to use the title dietitian or nutrition-
ist, but others allow only an RD or people with specified qualifica-
tions to call themselves dietitians. Many states provide a further
guarantee: a state registration, certification, or license to practice.
In this way, states identify people who have met minimal standards
of education and experience. Still, these state standards may fall short
of those defining an RD. Similarly, some alternative educational pro-
grams qualify their graduates as certified nutritionists, certified
nutritional consultants, or certified nutrition therapists—
terms that sound authoritative but lack the credentials of an RD.6
Dietitians perform a multitude of duties in many settings in most
communities. They work in the food industry, pharmaceutical com-
panies, home health agencies, long-term care institutions, private
practice, public health departments, research centers, education
settings, fitness centers, and hospitals. Depending on their work
settings, dietitians can assume a number of different job responsi-
bilities and positions. In hospitals, administrative dietitians manage
the foodservice system; clinical dietitians provide client care; and
nutrition support team dietitians coordinate nutrition care with
other health care professionals. In the food industry, dietitians con-
duct research, develop products, and market services.
Public health dietitians who work in government-funded
agencies play a key role in delivering nutrition services to people in
the community. Among their many roles, public health dietitians
help plan, coordinate, and evaluate food assistance programs; act as
consultants to other agencies; manage finances; and much more.
Other Dietary Employees
In some facilities, a dietetic technician assists registered dieti-
tians in both administrative and clinical responsibilities. A dietetic
technician has been educated and trained to work under the guid-
ance of a registered dietitian; upon passing a national examination,
the title changes to dietetic technician, registered (DTR).
accredited: approved; in the case
of medical centers or universities,
certified by an agency recognized
by the U.S. Department of
Education.
American Dietetic Association
(ADA): the professional
organization of dietitians in the
United States. The Canadian
equivalent is Dietitians of
Canada, which operates similarly.
certified nutritionists or certified
nutritional consultants or
certified nutrition therapists:
a person who has been granted
a document declaring his or
her authority as a nutrition
professional; see also
nutritionist.
correspondence schools: schools
that offer courses and degrees
by mail. Some correspondence
schools are accredited; others
are not.
dietetic technician: a person
who has completed a minimum
of an associate’s degree from an
accredited university or college
and an approved dietetic
technician program that
includes a supervised practice
experience. See also dietetic
technician, registered (DTR).
dietetic technician, registered
(DTR): a dietetic technician
who has passed a national
examination and maintains
registration through continuing
professional education.
dietitian: a person trained in
nutrition, food science, and diet
planning. See also registered
dietitian.
DTR: see dietetic technician,
registered.
fraudulent: the promotion, for
financial gain, of devices,
treatments, services, plans, or
products (including diets and
supplements) that alter or claim
to alter a human condition
without proof of safety or
effectiveness. (The word quackery
comes from the term quacksalver,
meaning a person who quacks
loudly about a miracle product—
a lotion or a salve.)
Internet (the net): a worldwide
network of millions of comput-
ers linked together to share
information.
license to practice: permission
under state or federal law,
granted on meeting specified
criteria, to use a certain title
(such as dietitian) and offer
certain services. Licensed
dietitians may use the initials
LD after their names.
misinformation: false or
misleading information.
nutritionist: a person who
specializes in the study of
nutrition. Note that this
definition does not specify
qualifications and may apply not
only to registered dietitians but
also to self-described experts
whose training is questionable.
Most states have licensing laws
that define the scope of practice
for those calling themselves
nutritionists.
public health dietitians:
dietitians who specialize in
providing nutrition services
through organized community
efforts.
RD: see registered dietitian.
registered dietitian (RD): a person
who has completed a minimum
of a bachelor’s degree from an
accredited university or college,
has completed approved course
work and a supervised practice
program, has passed a national
examination, and maintains
registration through continuing
professional education.
registration: listing; with respect
to health professionals, listing
with a professional organization
that requires specific course
work, experience, and passing
of an examination.
websites: Internet resources
composed of text and graphic
files, each with a unique URL
(Uniform Resource Locator) that
names the site (for example,
www.usda.gov).
World Wide Web (the web,
commonly abbreviated www):
a graphical subset of the
Internet.
GLOSSARY

In addition to the dietetic technician, other dietary
employees may include clerks, aides, cooks, porters,
and other assistants. These dietary employees do not
have extensive formal training in nutrition, and their
ability to provide accurate information may be limited.
Identifying Fake
Credentials
In contrast to registered dietitians, thousands of peo-
ple obtain fake nutrition degrees and claim to be nutri-
tion consultants or doctors of “nutrimedicine.” These
and other such titles may sound meaningful, but most
of these people lack the established credentials and
training of an ADA-sanctioned dietitian. If you look
closely, you can see signs of their fake expertise.
Consider educational background, for example. The
minimum standards of education for a dietitian specify
a bachelor of science (BS) degree in food science and
human nutrition or related fields from an accredited
college or university.* Such a degree generally requires
four to five years of study. In contrast, a fake nutrition
expert may display a degree from a six-month corre-
spondence course. Such a degree simply falls short. In
some cases, businesses posing as legitimate corre-
spondence schools offer even less—they sell certifi-
cates to anyone who pays the fees. To obtain these
“degrees,” a candidate need not attend any classes,
read any books, or pass any examinations.
To safeguard educational quality, an accrediting
agency recognized by the U.S. Department of Education
(DOE) certifies that certain schools meet criteria established to ensure
that an institution provides complete and accurate schooling. Unfortu-
nately, fake nutrition degrees are available from schools “accredited”
by more than 30 phony accrediting agencies. Acquiring false creden-
tials is especially easy today, with fraudulent businesses operating via
the Internet.
Knowing the qualifications of someone who provides nutrition
information can help you determine whether that person’s advice
might be harmful or helpful. Don’t be afraid to ask for credentials.
The accompanying “How to” lists credible sources of nutrition in-
formation.
Red Flags of Nutrition Quackery
Figure H1-2 (p. 34) features eight red flags consumers can use
to identify nutrition misinformation. Sales of unproven and
dangerous products have always been a concern, but the Inter-
HOW TO Find Credible Sources of Nutrition Information
Government agencies, volunteer associations, consumer groups, and profes-
sional organizations provide consumers with reliable health and nutrition infor-
mation. Credible sources of nutrition information include:
• Nutrition and food science departments at a university or community college
• Local agencies such as the health department or County Cooperative
Extension Service
• Government health agencies such as:
• Department of Agriculture (USDA) www.usda.gov
• Department of Health and Human
Services (DHHS) www.os.dhhs.gov
• Food and Drug Administration (FDA) www.fda.gov
• Health Canada www.hc-sc.gc.ca/nutrition
• Volunteer health agencies such as:
• American Cancer Society www.cancer.org
• American Diabetes Association www.diabetes.org
• American Heart Association www.americanheart.org
• Reputable consumer groups such as:
• American Council on Science and Health www.acsh.org
• Federal Citizen Information Center www.pueblo.gsa.gov
• International Food Information Council ific.org
• Professional health organizations such as:
• American Dietetic Assocation www.eatright.org
• American Medical Association www.ama-assn.org
• Dietitians of Canada www.dietitians.ca
• Journals such as:
• American Journal of Clinical Nutrition www.ajcn.org
• New England Journal of Medicine www.nejm.org
• Nutrition Reviews www.ilsi.org
net now provides merchants with an easy and inexpensive way to
reach millions of customers around the world. Because of the dif-
ficulty in regulating the Internet, fraudulent and illegal sales of
medical products have hit a bonanza. As is the case with the air,
no one owns the Internet, and similarly, no one has control over
the pollution. Countries have different laws regarding sales of
drugs, dietary supplements, and other health products, but apply-
ing these laws to the Internet marketplace is almost impossible.
Even if illegal activities could be defined and identified, finding the
person responsible for a particular website is not always possible.
Websites can open and close in a blink of a cursor. Now, more
than ever, consumers must heed the caution “Buyer beware.”
In summary, when you hear nutrition news, consider its source.
Ask yourself these two questions: Is the person providing the infor-
mation qualified to speak on nutrition? Is the information based
on valid scientific research? If not, find a better source. After all,
your health depends on it.
* To ensure the quality and continued improvement of nutrition and dietetics education programs, an ADA agency known as the Commission on Accreditation for
Dietetics Education (CADE) establishes and enforces eligibility requirements and accreditation standards for programs preparing students for careers as registered
dietitians or dietetic technicians. Programs meeting those standards are accredited by CADE.

34 • Highlight 1
Instant
recovery,
backto
your
everyday
schedule
The natural way to
becoming a better you
“Cures gout,
ulcers,
diabetes
and
cancer”
Guaranteed!
OR your
money
back!
“Best
pills
around”
Beats the hunger
stimulation point (HSP)
Revolutionary
product, based
on ancient
medicine
Money
grabbing
drug
companies
further
corporate
means
“M
y
friends
feel good
as new!”
Hearsay is the
weakest form of
evidence.
Such findings would be widely
publicized and accepted by
health professionals.
Time tested
Personal
testimonials
Phony terms hide
the lack of scientific
proof.
And this product’s
company doesn’t
want money?
At least the drug
company has
scientific research
proving the safety
and effectiveness
of its products.
Paranoid
accusations
Meaningless
medical jargon
Marketers may make
generous promises, but
consumers won’t be
able to collect on them.
Natural is not
necessarily better
or safer; any
product that is
strong enough
to be effective is
strong enough
to cause
side effects.
Natural
Satisfaction
guaranteed
No one product can possibly
treat such a diverse array of
conditions.
One product
does it all
Even proven
treatments
take time to
be effective.
Quick and
easy fixes
FIGURE H1-2 Red Flags of Nutrition Quackery
• Visit the National Council Against Health Fraud:
www.ncahf.org
• Find a registered dietitian in your area from the Ameri-
can Dietetic Association: www.eatright.org
• Find a nutrition professional in Canada from the Dieti-
tians of Canada: www.dietitians.ca
• Find out whether a correspondence school is accredited
from the Distance Education and Training Council’s
Accrediting Commission: www.detc.org
• Find useful and reliable health information from the
Health on the Net Foundation: www.hon.ch
• Find out whether a school is properly accredited for a
dietetics degree from the American Dietetic Association:
www.eatright.org/cade
• Obtain a listing of accredited institutions, profession-
ally accredited programs, and candidates for accredita-
tion from the American Council on Education:
www.acenet.edu
• Learn more about quackery from Stephen Barrett’s
Quackwatch: www.quackwatch.org
• Check out health-related hoaxes and urban legends:
www.cdc.gov/hoax_rumors.htm and
www.urbanlegends.com/
• Find reliable research articles: www.pubmed.gov

tion: Food and nutrition misinformation,
Journal of the American Dietetic Association
106 (2006): 601–607.
2. G. Eysenbach and coauthors, Empirical
studies assessing the quality of health infor-
mation for consumers on the World Wide
Web: A systematic review, Journal of the
American Medical Association 287 (2002):
2691–2700.
3. L. M. Schwartz, S. Woloshin, and L. Baczek,
Media coverage of scientific meetings: Too
much, too soon? Journal of the American
Medical Association 287 (2002): 2859–2863.
4. K. M. Adams and coauthors, Status of nutri-
tion education in medical schools, American
Journal of Clinical Nutrition 83 (2006):
941S–944S.
tion: The roles of registered dieticians and
dietetic technicians, registered in health
promotion and disease prevention, Journal
of the American Dietetic Association 106
(2006): 1875–1884.
6. Nutritionist imposters and how to spot
them, Nutrition and the M.D., September
2004, pp. 4–6.
REFERENCES

You make food choices—deciding what to eat and how much to eat—
more than 1000 times every year. We eat so frequently that it’s easy to
choose a meal without giving any thought to its nutrient contributions or
health consequences. Even when we want to make healthy choices, we
may not know which foods to select or how much to consume. With a
few tools and tips, you can learn to plan a healthy diet.
The CengageNOW logo
to interactive tutorials and videos based on your
level of understanding.
© PhotoLink/Getty Images

adequacy (dietary): providing all the
essential nutrients, fiber, and energy in
amounts sufficient to maintain health.
Chapter 1 explained that the body’s many activities are supported by the
nutrients delivered by the foods people eat. Food choices made over years
influence the body’s health, and consistently poor choices increase the risks
of developing chronic diseases. This chapter shows how a person can select
from the tens of thousands of available foods to create a diet that supports
health. Fortunately, most foods provide several nutrients, so one trick for
wise diet planning is to select a combination of foods that deliver a full ar-
ray of nutrients. This chapter begins by introducing the diet-planning prin-
ciples and dietary guidelines that assist people in selecting foods that will
deliver nutrients without excess energy (kcalories).
Principles and Guidelines
How well you nourish yourself does not depend on the selection of any one food. In-
stead, it depends on the selection of many different foods at numerous meals over
days, months, and years. Diet-planning principles and dietary guidelines are key
concepts to keep in mind whenever you are selecting foods—whether shopping at the
grocery store, choosing from a restaurant menu, or preparing a home-cooked meal.
Diet-Planning Principles
Diet planners have developed several ways to select foods. Whatever plan or combi-
nation of plans they use, though, they keep in mind the six basic diet-planning prin-
ciples ◆ listed in the margin.
Adequacy Adequacy means that the diet provides sufficient energy and enough
of all the nutrients to meet the needs of healthy people. Take the essential nutrient
iron, for example. Because the body loses some iron each day, people have to re-
place it by eating foods that contain iron. A person whose diet fails to provide
enough iron-rich foods may develop the symptoms of iron-deficiency anemia: the
person may feel weak, tired, and listless; have frequent headaches; and find that
even the smallest amount of muscular work brings disabling fatigue. To prevent
these deficiency symptoms, a person must include foods that supply adequate iron.
The same is true for all the other essential nutrients introduced in Chapter 1.
37
CHAPTER OUTLINE
Principles and Guidelines • Diet-Plan-
ning Principles • Dietary Guidelines for
Americans
Diet-Planning Guides • USDA Food
Guide • Exchange Lists • Putting the
Plan into Action • From Guidelines to
Groceries
Food Labels • The Ingredient List •
Serving Sizes • Nutrition Facts • The
Daily Values • Nutrient Claims • Health
Claims • Structure-Function Claims •
Consumer Education
HIGHLIGHT 2 Vegetarian Diets
2
Planning a
Healthy Diet
C H A P T E R
◆ Diet-planning principles:
• Adequacy
• Balance
• kCalorie (energy) control
• Nutrient Density
• Moderation
• Variety

38 • CHAPTER 2
balance (dietary): providing foods in
proportion to each other and in proportion
to the body’s needs.
kcalorie (energy) control: management of
food energy intake.
nutrient density: a measure of the nutrients
a food provides relative to the energy it
provides. The more nutrients and the fewer
kcalories, the higher the nutrient density.
Balance The art of balancing the diet involves consuming enough—but not too
much—of each type of food. The essential minerals calcium and iron, taken to-
gether, illustrate the importance of dietary balance. Meats, fish, and poultry are
rich in iron but poor in calcium. Conversely, milk and milk products are rich in cal-
cium but poor in iron. Use some meat or meat alternates for iron; use some milk and
milk products for calcium; and save some space for other foods, too, because a diet
consisting of milk and meat alone would not be adequate. ◆ For the other nutrients,
people need whole grains, vegetables, and fruits.
kCalorie (Energy) Control Designing an adequate diet without overeating re-
quires careful planning. Once again, balance plays a key role. The amount of
energy coming into the body from foods should balance with the amount of en-
ergy being used by the body to sustain its metabolic and physical activities. Up-
setting this balance leads to gains or losses in body weight. The discussion of
energy balance and weight control in Chapters 8 and 9 examines this issue in
more detail, but the key to kcalorie control is to select foods of high nutrient
density.
Nutrient Density To eat well without overeating, select foods that deliver the
most nutrients for the least food energy. Consider foods containing calcium, for
example. You can get about 300 milligrams of calcium from either 11/2 ounces of
cheddar cheese or 1 cup of fat-free milk, but the cheese delivers about twice as
much food energy (kcalories) as the milk. The fat-free milk, then, is twice as cal-
cium dense as the cheddar cheese; it offers the same amount of calcium for half
the kcalories. Both foods are excellent choices for adequacy’s sake alone, but to
achieve adequacy while controlling kcalories, ◆ the fat-free milk is the better
choice. (Alternatively, a person could select a low-fat cheddar cheese.) The many
bar graphs that appear in Chapters 10 through 13 highlight the most nutrient-
dense choices, and the accompanying “How to” describes how to compare foods
based on nutrient density.
◆ Balance in the diet helps to ensure
adequacy.
◆ Nutrient density promotes adequacy and
kcalorie control.
One way to evaluate foods is simply to notice
their nutrient contribution per serving: 1 cup
of milk provides about 300 milligrams of cal-
cium, and
1
⁄2 cup of fresh, cooked turnip
greens provides about 100 milligrams. Thus a
serving of milk offers three times as much cal-
cium as a serving of turnip greens. To get 300
milligrams of calcium, a person could choose
either 1 cup of milk or 1
1
⁄2 cups of turnip
greens.
Another valuable way to evaluate foods is
to consider their nutrient density—their nu-
trient contribution per kcalorie. Fat-free milk
delivers about 85 kcalories with its 300 mil-
ligrams of calcium. To calculate the nutrient
density, divide milligrams by kcalories:
300 mg calcium
3.5 mg per kcal
85 kcal
Do the same for the fresh turnip greens,
which provide 15 kcalories with the 100 mil-
ligrams of calcium:
100 mg calcium
6.7 mg per kcal
15 kcal
The more milligrams per kcalorie, the
greater the nutrient density. Turnip greens
are more calcium dense than milk. They pro-
vide more calcium per kcalorie than milk, but
milk offers more calcium per serving. Both ap-
proaches offer valuable information, espe-
cially when combined with a realistic
appraisal. What matters most is which are
you more likely to consume—1
1
⁄2 cups of
turnip greens or 1 cup of milk? You can get
300 milligrams of calcium from either, but
the greens will save you about 40 kcalories
(the savings would be even greater if you
usually use whole milk).
Keep in mind, too, that calcium is only
one of the many nutrients that foods provide.
Similar calculations for protein, for example,
would show that fat-free milk provides more
protein both per kcalorie and per serving than
turnip greens—that is, milk is more protein
dense. Combining variety with nutrient den-
sity helps to ensure the adequacy of all
nutrients.
HOW TO Compare Foods Based on Nutrient Density
To ensure an adequate and balanced diet, eat
a variety of foods daily, choosing different
foods from each group.
©
Polara
Sutdios
Inc.
To practice comparing the nutrient density of foods,
log on to academic.cengage.com/login, go to

PLANNING A HEALTHY DIET • 39
Just like a person who has to pay for rent, food, clothes, and tuition on a lim-
ited budget, we have to obtain iron, calcium, and all the other essential nutrients
on a limited energy allowance. Success depends on getting many nutrients for
each kcalorie “dollar.” For example, a can of cola and a handful of grapes may
both provide about the same number of kcalories, but the grapes deliver many
more nutrients. A person who makes nutrient-dense choices, such as fruit instead
of cola, can meet daily nutrient needs on a lower energy budget. Such choices sup-
port good health.
Foods that are notably low in nutrient density—such as potato chips, candy, and
colas—are sometimes called empty-kcalorie foods. The kcalories these foods
provide are called “empty” because they deliver energy (from sugar, fat, or both)
with little, or no, protein, vitamins, or minerals.
Moderation Foods rich in fat and sugar provide enjoyment and energy but rela-
tively few nutrients. In addition, they promote weight gain when eaten in excess. A
person practicing moderation ◆ eats such foods only on occasion and regularly se-
lects foods low in solid fats and added sugars, a practice that automatically im-
proves nutrient density. Returning to the example of cheddar cheese versus fat-free
milk, the fat-free milk not only offers the same amount of calcium for less energy,
but it also contains far less fat than the cheese.
Variety A diet may have all of the virtues just described and still lack variety, if
a person eats the same foods day after day. People should select foods from each
of the food groups daily and vary their choices within each food group from day
to day for several reasons. First, different foods within the same group contain dif-
ferent arrays of nutrients. Among the fruits, for example, strawberries are espe-
cially rich in vitamin C while apricots are rich in vitamin A. Variety improves
nutrient adequacy.1 Second, no food is guaranteed entirely free of substances that,
in excess, could be harmful. The strawberries might contain trace amounts of one
contaminant, the apricots another. By alternating fruit choices, a person will in-
gest very little of either contaminant. Third, as the adage goes, variety is the spice
of life. A person who eats beans frequently can enjoy pinto beans in Mexican bur-
ritos today, garbanzo beans in Greek salad tomorrow, and baked beans with bar-
becued chicken on the weekend. Eating nutritious meals need never be boring.
Dietary Guidelines for Americans
What should a person eat to stay healthy? The answers can be found in the Di-
etary Guidelines for Americans 2005. These guidelines provide science-based ad-
vice to promote health and to reduce risk of chronic diseases through diet and
physical activity.2 Table 2-1 presents the nine Dietary Guidelines topics with their
key recommendations. These key recommendations, along with additional rec-
ommendations for specific population groups, also appear throughout the text
as their subjects are discussed. The first three topics focus on choosing nutrient-
dense foods within energy needs, maintaining a healthy body weight, and en-
gaging in regular physical activity. The fourth topic, “Food Groups to
Encourage,” focuses on the selection of a variety of fruits and vegetables, whole
grains, and milk. The next four topics advise people to choose sensibly in their
use of fats, carbohydrates, salt, and alcoholic beverages (for those who partake).
Finally, consumers are reminded to keep foods safe. Together, the Dietary Guide-
lines point the way toward better health. Table 2-2 presents Canada’s Guidelines
for Healthy Eating.
Some people might wonder why dietary guidelines include recommendations for
physical activity. The simple answer is that most people who maintain a healthy
body weight do more than eat right. They also exercise—the equivalent of 60 min-
utes or more of moderately intense physical activity daily. As you will see repeat-
edly throughout this text, food and physical activity choices are integral partners
in supporting good health.
empty-kcalorie foods: a popular term used
to denote foods that contribute energy but
lack protein, vitamins, and minerals.
moderation (dietary): providing enough
but not too much of a substance.
variety (dietary): eating a wide selection
of foods within and among the major food
groups.
◆ Moderation contributes to adequacy,
balance, and kcalorie control.

40 • CHAPTER 2
TABLE 2-1 Key Recommendations of the Dietary Guidelines
for Americans 2005
Adequate Nutrients within Energy Needs
• Consume a variety of nutrient-dense foods and beverages within and among the basic food
groups; limit intakes of saturated and trans fats, cholesterol, added sugars, salt, and alcohol.
• Meet recommended intakes within energy needs by adopting a balanced eating pattern, such
as the USDA Food Guide (see pp. 41–47).
Weight Management
• To maintain body weight in a healthy range, balance kcalories from foods and beverages with
kcalories expended (see Chapters 8 and 9).
• To prevent gradual weight gain over time, make small decreases in food and beverage kcalories
and increase physical activity.
Physical Activity
• Engage in regular physical activity and reduce sedentary activities to promote health, psycho-
logical well-being, and a healthy body weight.
• Achieve physical fitness by including cardiovascular conditioning, stretching exercises for flexi-
bility, and resistance exercises or calisthenics for muscle strength and endurance.
Food Groups to Encourage
• Consume a sufficient amount of fruits, vegetables, milk and milk products, and whole grains
while staying within energy needs.
• Select a variety of fruits and vegetables each day, including selections from all five vegetable
subgroups (dark green, orange, legumes, starchy vegetables, and other vegetables) several
times a week. Make at least half of the grain selections whole grains. Select fat-free or low-fat
milk products.
Fats
• Consume less than 10 percent of kcalories from saturated fats and less than 300 milligrams of
cholesterol per day, and keep trans fats consumption as low as possible (see Chapter 5).
• Keep total fat intake between 20 and 35 percent of kcalories; choose from mostly polyunsatu-
rated and monounsaturated fat sources such as fish, nuts, and vegetable oils.
• Select and prepare foods that are lean, low fat, or fat-free and low in saturated and/or trans
fats.
Carbohydrates
• Choose fiber-rich fruits, vegetables, and whole grains often.
• Choose and prepare foods and beverages with little added sugars (see Chapter 4).
• Reduce the incidence of dental caries by practicing good oral hygiene and consuming sugar-
and starch-containing foods and beverages less frequently.
Sodium and Potassium
• Choose and prepare foods with little salt (less than 2300 milligrams sodium or approximately 1
teaspoon salt daily). At the same time, consume potassium-rich foods, such as fruits and veg-
etables (see Chapter 12).
Alcoholic Beverages
• Those who choose to drink alcoholic beverages should do so sensibly and in moderation (up to
one drink per day for women and up to two drinks per day for men).
• Some individuals should not consume alcoholic beverages (see Highlight 7).
Food Safety
• To avoid microbial foodborne illness, keep foods safe: clean hands, food contact surfaces, and
fruits and vegetables; separate raw, cooked, and ready-to-eat foods; cook foods to a safe inter-
nal temperature; chill perishable food promptly; and defrost food properly.
• Avoid unpasteurized milk and products made from it; raw or undercooked eggs, meat, poultry,
fish, and shellfish; unpasteurized juices; raw sprouts.
NOTE: These guidelines are intended for adults and healthy children ages 2 and older.
SOURCE: The Dietary Guidelines for Americans 2005, available at www.healthierus.gov/dietaryguidelines.
TABLE 2-2 Canada’s Guidelines
for Healthy Eating
• Enjoy a variety of foods.
• Emphasize cereals, breads, other grain prod-
ucts, vegetables, and fruits.
• Choose lower-fat dairy products, leaner meats,
and foods prepared with little or no fat.
• Achieve and maintain a healthy body weight
by enjoying regular physical activity and
healthy eating.
• Limit salt, alcohol, and caffeine.
SOURCE: These guidelines derive from Action Towards Healthy
Eating—Canada’s Guidelines for Healthy Eating and Recom-
mended Strategies for Implementation.

TABLE 2-3 Recommended Daily Amounts from Each Food Group
Diet-Planning Guides
To plan a diet that achieves all of the dietary ideals just outlined, a person needs
tools as well as knowledge. Among the most widely used tools for diet planning are
food group plans that build a diet from clusters of foods that are similar in nutri-
ent content. Thus each group represents a set of nutrients that differs somewhat
from the nutrients supplied by the other groups. Selecting foods from each of the
groups eases the task of creating an adequate and balanced diet.
USDA Food Guide
The 2005 Dietary Guidelines encourage consumers to adopt a balanced eating plan,
such as the USDA’s Food Guide (see Figure 2-1 on pp. 42–43). The USDA Food
Guide assigns foods to five major groups ◆ and recommends daily amounts of
foods from each group to meet nutrient needs. In addition to presenting the food
groups, the figure lists the most notable nutrients of each group, the serving equiv-
alents, and the foods within each group sorted by nutrient density. Chapter 15
provides a food guide for young children, and Appendix I presents Canada’s food
group plan, the Food Guide to Healthy Eating.
Meet recommended intakes within energy needs by adopting a balanced
eating pattern, such as the USDA Food Guide or the DASH eating plan.
(The DASH eating plan is presented in Chapter 12.)
◆ Five food groups:
• Fruits
• Vegetables
• Grains
• Meat and legumes
• Milk
A well-planned diet delivers adequate nutrients, a balanced array of nutri-
ents, and an appropriate amount of energy. It is based on nutrient-dense
foods, moderate in substances that can be detrimental to health, and varied
in its selections. The 2005 Dietary Guidelines apply these principles, offering
practical advice on how to eat for good health.
IN SUMMARY
Recommended Amounts All food groups offer valuable nutrients, and people
should make selections from each group daily. Table 2-3 specifies the amounts of
foods from each group needed daily to create a healthful diet for several energy
(kcalorie) levels. ◆ Estimated daily kcalorie needs for sedentary and active men and
1600 kcal 1800 kcal 2000 kcal 2200 kcal 2400 kcal 2600 kcal 2800 kcal 3000 kcal
Fruits 11
⁄2 c 11
⁄2 c 2 c 2 c 2 c 2 c 21
⁄2 c 21
⁄2 c
Vegetables 2 c 21
⁄2 c 21
⁄2 c 3 c 3 c 31
⁄2 c 31
⁄2 c 4 c
Grains 5 oz 6 oz 6 oz 7 oz 8 oz 9 oz 10 oz 10 oz
Meat and legumes 5 oz 5 oz 51
⁄2 oz 6 oz 61
⁄2 oz 61
⁄2 oz 7 oz 7 oz
Milk 3 c 3 c 3 c 3 c 3 c 3 c 3 c 3 c
Oils 5 tsp 5 tsp 6 tsp 6 tsp 7 tsp 8 tsp 8 tsp 10 tsp
Discretionary 132 kcal 195 kcal 267 kcal 290 kcal 362 kcal 410 kcal 426 kcal 512 kcal
kcalorie allowance
◆ Chapter 8 explains how to determine energy
needs. For an approximation, turn to the
DRI Estimated Energy Requirement (EER) on
the inside front cover.
food group plans: diet-planning tools that
sort foods into groups based on nutrient
content and then specify that people should
eat certain amounts of foods from each
group.

42 • CHAPTER 2
FIGURE 2-1 USDA Food Guide, 2005
Choose a variety of vegetables from all five subgroups several times a week.
These foods contribute folate, vitamin A, vitamin C, vitamin K, vitamin E, magnesium,
potassium, and fiber.
1
⁄2 c vegetables is equivalent to 1
⁄2 c cut-up raw or cooked vegetables;
1
⁄2 c cooked legumes; 1
⁄2 c vegetable juice; 1 c raw, leafy greens.
Dark green vegetables: Broccoli and leafy greens such as arugula, beet greens, bok
choy, collard greens, kale, mustard greens, romaine lettuce, spinach, and turnip
greens.
Orange and deep yellow vegetables: Carrots, carrot juice, pumpkin, sweet potatoes,
and winter squash (acorn, butternut).
Legumes: Black beans, black-eyed peas, garbanzo beans (chickpeas), kidney
beans, lentils, navy beans, pinto beans, soybeans and soy products such as tofu,
and split peas.
Starchy vegetables: Cassava, corn, green peas, hominy, lima beans, and potatoes.
Other vegetables: Artichokes, asparagus, bamboo shoots, bean sprouts, beets,
brussels sprouts, cabbages, cactus, cauliflower, celery, cucumbers, eggplant, green
beans, iceberg lettuce, mushrooms, okra, onions, peppers, seaweed, snow peas,
tomatoes, vegetable juices, zucchini.
Baked beans, candied sweet potatoes, coleslaw, French fries, potato salad, refried
beans, scalloped potatoes, tempura vegetables.
VEGETABLES
Consume a variety of fruits and no more than one-third of the recommended
intake as fruit juice.
These foods contribute folate, vitamin A, vitamin C, potassium, and fiber.
1
⁄2 c fruit is equivalent to 1
⁄2 c fresh, frozen, or canned fruit; 1 small
fruit; 1
⁄4 c dried fruit; 1
⁄2 c fruit juice.
Apples, apricots, avocados, bananas, blueberries, cantaloupe, cherries, grapefruit,
grapes, guava, kiwi, mango, oranges, papaya, peaches, pears, pineapples, plums,
raspberries, strawberries, watermelon; dried fruit (dates, figs, raisins); unsweetened
juices.
Canned or frozen fruit in syrup; juices, punches, ades, and fruit drinks with added
sugars; fried plantains.
FRUITS
© Polara Studios, Inc.
Make at least half of the grain selections whole grains.
These foods contribute folate, niacin, riboflavin, thiamin, iron, magnesium, selenium,
and fiber.
1 oz grains is equivalent to 1 slice bread; 1
⁄2 c cooked rice, pasta, or
cereal; 1 oz dry pasta or rice; 1 c ready-to-eat cereal; 3 c popped popcorn.
Whole grains (amaranth, barley, brown rice, buckwheat, bulgur, millet, oats, quinoa,
rye, wheat) and whole-grain, low-fat breads, cereals, crackers, and pastas; popcorn.
Enriched bagels, breads, cereals, pastas (couscous, macaroni, spaghetti), pretzels,
rice, rolls, tortillas.
Biscuits, cakes, cookies, cornbread, crackers, croissants, doughnuts, French toast,
fried rice, granola, muffins, pancakes, pastries, pies, presweetened cereals, taco
shells, waffles.
GRAINS
Key:
Foods lower in nutrient density (limit selections)
Foods generally high in nutrient density (choose most often)

FIGURE 2-1 USDA Food Guide, 2005, continued
MEAT, POULTRY, FISH,
LEGUMES, EGGS, AND NUTS
Matthew Farruggio
Matthew Farruggio
Make lean or low-fat choices. Prepare them with little, or no, added fat.
Meat, poultry, fish, and eggs contribute protein, niacin, thiamin, vitamin B6, vitamin B12,
iron, magnesium, potassium, and zinc; legumes and nuts are notable for their protein,
folate, thiamin, vitamin E, iron, magnesium, potassium, zinc, and fiber.
1 oz meat is equivalent to 1 oz cooked lean meat, poultry, or fish; 1 egg;
1
⁄4 c cooked legumes or tofu; 1 tbs peanut butter; 1
⁄2 oz nuts or seeds.
Poultry (no skin), fish, shellfish, legumes, eggs, lean meat (fat-trimmed beef, game,
ham, lamb, pork); low-fat tofu, tempeh, peanut butter, nuts (almonds, filberts,
peanuts, pistachios, walnuts) or seeds (flaxseeds, pumpkin seeds, sunflower
seeds).
Bacon; baked beans; fried meat, fish, poultry, eggs, or tofu; refried beans; ground
beef; hot dogs; luncheon meats; marbled steaks; poultry with skin; sausages; spare
ribs.
Select the recommended amounts of oils from among these sources.
These foods contribute vitamin E and essential fatty acids (see Chapter 5), along with
abundant kcalories.
1 tsp oil is equivalent to 1 tbs low-fat mayonnaise; 2 tbs light salad
dressing; 1 tsp vegetable oil; 1 tsp soft margarine.
Liquid vegetable oils such as canola, corn, flaxseed, nut, olive, peanut, safflower,
sesame, soybean, and sunflower oils; mayonnaise, oil-based salad dressing, soft
trans-free margarine.
Unsaturated oils that occur naturally in foods such as avocados, fatty fish, nuts,
olives,
seeds (flaxseeds, sesame seeds), and shellfish.
Limit intakes of food and beverages with solid fats and added sugars.
Solid fats deliver saturated fat and trans fat, and intake should be kept low.
Solid fats and added sugars contribute abundant kcalories but few nutrients, and
intakes should not exceed the discretionary kcalorie allowance—kcalories to meet
energy needs after all nutrient needs have been met with nutrient-dense foods.
Alcohol also contributes abundant kcalories but few nutrients, and its kcalories are
counted among discretionary kcalories. See Table 2-3 for some discretionary kcalorie
allowances.
Solid fats that occur in foods naturally such as milk fat and meat fat (see in
previous lists).
Solid fats that are often added to foods such as butter, cream cheese, hard
margarine, lard, sour cream, and shortening.
Added sugars such as brown sugar, candy, honey, jelly, molasses, soft drinks,
sugar, and syrup.
Alcoholic beverages include beer, wine, and liquor.
Make fat-free or low-fat choices. Choose lactose-free products or other
calcium-rich foods if you don't consume milk.
These foods contribute protein, riboflavin, vitamin B12, calcium, magnesium,
potassium, and, when fortified, vitamin A and vitamin D.
1 c milk is equivalent to 1 c fat-free milk or yogurt; 11⁄2 oz fat-free natural
cheese; 2 oz fat-free processed cheese.
Fat-free milk and fat-free milk products such as buttermilk, cheeses, cottage
cheese, yogurt; fat-free fortified soy milk.
1% low-fat milk, 2% reduced-fat milk, and whole milk; low-fat, reduced-fat, and
whole-milk products such as cheeses, cottage cheese, and yogurt; milk products
with added sugars such as chocolate milk, custard, ice cream, ice milk, milk shakes,
pudding, sherbet; fortified soy milk.
MILK,YOGURT, AND CHEESE
OILS
SOLID FATS AND ADDED SUGARS

TABLE 2-5 Recommended Weekly Amounts from the Vegetable Subgroups
44 • CHAPTER 2
women are shown in Table 2-4. A sedentary young women needing 2000 kcalories
a day, for example, would select 2 cups of fruit; 21/2 cups of vegetables (dispersed
among the vegetable subgroups); 6 ounces of grain foods (with at least half coming
from whole grains); 51/2 ounces of meat, poultry, or fish, or the equivalent of
legumes, eggs, seeds, or nuts; and 3 cups of milk or yogurt, or the equivalent
amount of cheese or fortified soy products. Additionally, a small amount of unsatu-
rated oil, such as vegetable oil, or the oils of nuts, olives, or fatty fish, is required to
supply needed nutrients.
All vegetables provide an array of vitamins, fiber, and the mineral potassium,
but some vegetables are especially good sources of certain nutrients and beneficial
phytochemicals. ◆ For this reason, the USDA Food Guide sorts the vegetable group
into five subgroups. The dark green vegetables deliver the B vitamin folate; the or-
ange vegetables provide vitamin A; legumes supply iron and protein; the starchy
vegetables contribute carbohydrate energy; and the other vegetables fill in the gaps
and add more of these same nutrients.
In a 2000-kcalorie diet, then, the recommended 21/2 cups of daily vegetables
should be varied among the subgroups over a week’s time, as shown in Table 2-5.
In other words, consuming 21/2 cups of potatoes or even nutrient-rich spinach every
day for seven days does not meet the recommended vegetable intakes. Potatoes and
spinach make excellent choices when consumed in balance with vegetables from
other subgroups. Intakes of vegetables are appropriately averaged over a week’s
time—it is not necessary to include every subgroup every day.
Notable Nutrients As Figure 2-1 notes, each food group contributes key nutri-
ents. This feature provides flexibility in diet planning because a person can select
any food from a food group and receive similar nutrients. For example, a person can
choose milk, cheese, or yogurt and receive the same key nutrients. Importantly,
foods provide not only these key nutrients, but small amounts of other nutrients and
phytochemicals as well.
Because legumes contribute the same key nutrients—notably, protein, iron, and
zinc—as meats, poultry, and fish, they are included in the same food group. For this
reason, legumes are useful as meat alternatives, and they are also excellent sources
of fiber and the B vitamin folate. To encourage frequent consumption, the USDA
Food Guide also includes legumes as a subgroup of the vegetable group. Thus
legumes count in either the vegetable group or the meat and legume group. In gen-
eral, people who regularly eat meat, poultry, and fish count legumes as a veg-
etable, and vegetarians and others who seldom eat meat, poultry, or fish count
legumes in the meat and legumes group.
The USDA Food Guide encourages greater consumption from certain food
groups to provide the nutrients most often lacking ◆ in the diets of Americans. In
general, most people need to eat:
• More dark green vegetables, orange vegetables, legumes, fruits, whole
grains, and low-fat milk and milk products
TABLE 2-4 Estimated Daily
kCalorie Needs for Adults
Sedentarya Activeb
Women
19–30 yr 2000 2400
31–50 yr 1800 2200
51+ yr 1600 2100
Men
19–30 yr 2400 3000
31–50 yr 2200 2900
51+ yr 2000 2600
aSedentary describes a lifestyle that includes only the activities
typical of day-to-day life.
bActive describes a lifestyle that includes physical activity equivalent
to walking more than 3 miles per day at a rate of 3 to 4 miles per
hour, in addition to the activities typical of day-to-day life. kCalorie
values for active people reflect the midpoint of the range appropriate
for age and gender, but within each group, older adults may need
fewer kcalories and younger adults may need more.
NOTE: In addition to gender, age, and activity level, energy needs
vary with height and weight (see Chapter 8 and Appendix F).
◆ The USDA nutrients of concern are fiber, vi-
tamin A, vitamin C, vitamin E, and the min-
erals calcium, magnesium, and potassium.
◆ Reminder: Phytochemicals are the nonnutri-
ent compounds found in plant-derived foods
that have biological activity in the body.
Table 2-3 specifies the recommended amounts of total vegetables per day. This table shows those amounts dispersed among five vegetable subgroups per week.
Vegetable 1600 1800 2000 2200 2400 2600 2800 3000
Subgroups kcal kcal kcal kcal kcal kcal kcal kcal
Dark green 2 c 3 c 3 c 3 c 3 c 3 c 3 c 3 c
Orange and deep yellow 11
⁄2 c 2 c 2 c 2 c 2 c 21
⁄2 c 21
⁄2 c 21
⁄2 c
Legumes 21
⁄2 c 3 c 3 c 3 c 3 c 31
⁄2 c 31
⁄2 c 31
⁄2 c
Starchy 21
⁄2 c 3 c 3 c 6 c 6 c 7 c 7 c 9 c
Other 51
⁄2 c 61
⁄2 c 61
⁄2 c 7 c 7 c 81
⁄2 c 81
⁄2 c 10 c
legumes (lay-GYOOMS, LEG-yooms): plants
of the bean and pea family, with seeds that
are rich in protein compared with other
plant-derived foods.

Energy intake
to meet nutrient
needs
Discretionary
kcalorie
allowance
Energy
allowance
to maintain
weight
0
500
1000
1500 1733
267
2000
kCalories
• Less refined grains, total fats (especially saturated fat, trans fat, and choles-
terol), added sugars, and total kcalories
Nutrient Density The USDA Food Guide provides a foundation for a healthy diet
by emphasizing nutrient-dense options within each food group. By consistently se-
lecting nutrient-dense foods, a person can obtain all the nutrients needed and still
keep kcalories under control. In contrast, eating foods that are low in nutrient den-
sity makes it difficult to get enough nutrients without exceeding energy needs and
gaining weight. For this reason, consumers should select low-fat foods from each
group and foods without added fats or sugars—for example, fat-free milk instead of
whole milk, baked chicken without the skin instead of hot dogs, green beans instead
of French fries, orange juice instead of fruit punch, and whole-wheat bread instead
of biscuits. Notice that the key in Figure 2-1 indicates which foods within each group
are high or low in nutrient density. Oil is a notable exception: even though oil is
pure fat and therefore rich in kcalories, a small amount of oil from sources such as
nuts, fish, or vegetable oils is necessary every day to provide nutrients lacking from
other foods. Consequently these high-fat foods are listed among the nutrient-dense
foods (see Highlight 5 to learn why).
Consume a variety of nutrient-dense foods and beverages within and
among the basic food groups while choosing foods that limit the intake of
saturated and trans fats, cholesterol, added sugars, salt, and alcohol.
Discretionary kCalorie Allowance At each kcalorie level, people who consis-
tently choose nutrient-dense foods may be able to meet their nutrient needs without
consuming their full allowance of kcalories. The difference between the kcalories
needed to supply nutrients and those needed for energy—known as the discre-
tionary kcalorie allowance—is illustrated in Figure 2-2. Table 2-3 (p. 41) includes
the discretionary kcalorie allowance for several kcalorie levels. A person with dis-
cretionary kcalories available might choose to:
• Eat additional nutrient-dense foods, such as an extra serving of skinless
chicken or a second ear of corn.
• Select a few foods with fats or added sugars, such as reduced-fat milk or
sweetened cereal.
• Add a little fat or sugar to foods, such as butter or jelly on toast.
• Consume some alcohol. (Highlight 7 explains why this may not be a good
choice for some individuals.)
Alternatively, a person wanting to lose weight might choose to:
• Not use the kcalories available from the discretionary kcalorie allowance.
Added fats and sugars are always counted as discretionary kcalories. The kcalo-
ries from the fat in higher-fat milks and meats are also counted among discre-
tionary kcalories. It helps to think of fat-free milk as “milk” and whole milk or
reduced-fat milk as “milk with added fat.” Similarly, “meats” should be the leanest;
other cuts are “meats with added fat.” Puddings and other desserts made from
whole milk provide discretionary kcalories from both the sugar added to sweeten
them and the naturally occurring fat in the whole milk they contain. Even fruits,
vegetables, and grains can carry discretionary kcalories into the diet in the form of
peaches canned in syrup, scalloped potatoes, or high-fat crackers.
Discretionary kcalories must be counted separately from the kcalories of the nu-
trient-dense foods of which they may be a part. A fried chicken leg, for example,
provides discretionary kcalories from two sources: the naturally occurring fat of the
chicken skin and the added fat absorbed during frying. The kcalories of the skinless
chicken underneath are not discretionary kcalories—they are necessary to provide
the nutrients of chicken.
FIGURE 2-2 Discretionary kCalorie
Allowance for a 2000-kCalorie
Diet Plan
discretionary kcalorie allowance: the
kcalories remaining in a person’s energy
allowance after consuming enough nutrient-
dense foods to meet all nutrient needs for
a day.

46 • CHAPTER 2
Serving Equivalents Recommended serving amounts for fruits, vegetables, and
milk are measured in cups and those for grains and meats, in ounces. Figure 2-1 pro-
vides equivalent measures among the foods in each group specifying, for example,
that 1 ounce of grains is equivalent to 1 slice of bread or 1/2 cup of cooked rice.
A person using the USDA Food Guide can become more familiar with measured
portions by determining the answers to questions such as these: ◆ What portion of
a cup is a small handful of raisins? Is a “helping” of mashed potatoes more or less
than a half-cup? How many ounces of cereal do you typically pour into the bowl?
How many ounces is the steak at your favorite restaurant? How many cups of milk
does your glass hold? Figure 2-1 (pp. 42–43) includes the serving sizes and equiva-
lent amounts for foods within each group.
Mixtures of Foods Some foods—such as casseroles, soups, and sandwiches—fall
into two or more food groups. With a little practice, users can learn to see these mix-
tures of foods as items from various food groups. For example, from the USDA Food
Guide point of view, a taco represents four different food groups: the taco shell from
the grains group; the onions, lettuce, and tomatoes from the “other vegetables”
group; the ground beef from the meat group; and the cheese from the milk group.
Vegetarian Food Guide Vegetarian diets rely mainly on plant foods: grains,
vegetables, legumes, fruits, seeds, and nuts. Some vegetarian diets include eggs, milk
products, or both. People who do not eat meats or milk products can still use the
USDA Food Guide to create an adequate diet.3
◆ The food groups are similar, and
the amounts for each serving remain the same. Highlight 2 defines vegetarian terms
and provides details on planning healthy vegetarian diets.
Ethnic Food Choices People can use the USDA Food Guide and still enjoy a di-
verse array of culinary styles by sorting ethnic foods into their appropriate food
groups. For example, a person eating Mexican foods would find tortillas in the
grains group, jicama in the vegetable group, and guava in the fruit group. Table
2-6 features ethnic food choices.
TABLE 2-6 Ethnic Food Choices
◆ For quick and easy estimates, visualize each
portion as being about the size of a common
object:
• 1 c fruit or vegetables = a baseball
• 1/4 c dried fruit = a golf ball
• 3 oz meat = a deck of cards
• 2 tbs peanut butter = a marshmallow
• 11/2 oz cheese = 6 stacked dice
• 1/2 c ice cream = a racquetball
• 4 small cookies = 4 poker chips
Grains
Asian
Vegetables Fruits Meats and legumes Milk
Pita pocket
bread, pastas,
rice, couscous,
polenta, bulgur,
focaccia, Italian
bread
Eggplant,
tomatoes,
peppers,
cucumbers,
grape leaves
Olives,
grapes,
figs
Ricotta,
provolone,
parmesan,
feta,
mozzarella,
and goat
cheeses;
yogurt
Fish and other
seafood, gyros,
lamb, chicken,
beef, pork,
sausage, lentils,
fava beans
Tortillas (corn
or flour),
taco shells,
rice
Chayote, corn,
jicama, tomato
salsa, cactus,
cassava,
tomatoes,
yams, chilies
Guava,
mango,
papaya,
avocado,
plantain,
bananas,
oranges
Cheese,
custard
Refried beans,
fish, chicken,
chorizo, beef,
eggs
Mediterranean
Mexican
Rice, noodles,
millet
Amaranth, baby
corn, bamboo
shoots, chayote,
bok choy, mung
bean sprouts,
sugar peas, straw
mushrooms, water
chestnuts, kelp
Carambola,
guava,
kumquat,
lychee,
persimmon,
melons,
mandarin
orange
Usually
excluded
Soybeans and soy
products such as
soy milk and tofu,
squid, duck eggs,
pork, poultry, fish
and other seafood,
peanuts, cashews
©
Becky
Luigart-Stayner/Corbis
©
Photo
Disc/Getty
Images
©
Photo
Disc/Getty
Images

OILS
VEGETABLES FRUITS MILK MEAT BEANS
GRAINS
A person climbing steps
reminds consumers to
be physically active
each day.
The narrow slivers of
color at the top imply
moderation in foods rich
in solid fats and added
sugars.
The wide bottom
represents nutrient-dense
foods that should make
up the bulk of the diet.
The multiple colors of the pyramid illustrate variety:
each color represents one of the five food groups,
plus one for oils. Different widths of colors suggest
the proportional contribution of each food group to
a healthy diet.
Greater intakes of grains,
vegetables, fruits, and
milk are encouraged by
the width of orange,
green, red, and blue,
respectively.
The name, slogan, and
website present a
personalized approach.
MyPyramid—Steps to a Healthier You The USDA created an educational tool
called MyPyramid to illustrate the concepts of the Dietary Guidelines and the USDA
Food Guide. Figure 2-3 presents a graphic image of MyPyramid, which was de-
signed to encourage consumers to make healthy food and physical activity
choices every day.
The abundant materials that support MyPyramid help consumers choose the
kinds and amounts of foods to eat each day (MyPyramid.gov). In addition to cre-
ating a personal plan, consumers can find tips to help them improve their diet and
lifestyle by “taking small steps each day.”
Exchange Lists
Food group plans are particularly well suited to help a person achieve dietary ade-
quacy, balance, and variety. Exchange lists provide additional help in achieving
kcalorie control and moderation. Originally developed for people with diabetes, ex-
change systems have proved useful for general diet planning as well.
Unlike the USDA Food Guide, which sorts foods primarily by their vitamin and
mineral contents, the exchange system sorts foods according to their energy-nutri-
ent contents. Consequently, foods do not always appear on the exchange list where
you might first expect to find them. For example, cheeses are grouped with meats
because, like meats, cheeses contribute energy from protein and fat but provide
negligible carbohydrate. (In the USDA Food Guide presented earlier, cheeses are
grouped with milk because they are milk products with similar calcium contents.)
FIGURE 2-3 MyPyramid: Steps to a Healthier You
SOURCE: USDA, 2005
◆ MyPyramid.gov offers information on
vegetarian diets in its Tips Resources
section.
exchange lists: diet-planning tools that
organize foods by their proportions of
carbohydrate, fat, and protein. Foods on
any single list can be used interchangeably.

TABLE 2-7 Diet Planning Using the USDA Food Guide
48 • CHAPTER 2
For similar reasons, starchy vegetables such as corn, green peas, and potatoes are
listed with grains on the starch list in the exchange system, rather than with the veg-
etables. Likewise, olives are not classed as a “fruit” as a botanist would claim; they are
classified as a “fat” because their fat content makes them more similar to oil than to
berries. Bacon and nuts are also on the fat list to remind users of their high fat content.
These groupings highlight the characteristics of foods that are significant to energy in-
take. To learn more about this useful diet-planning tool, study Appendix G, which
gives details of the exchange system used in the United States, and Appendix I, which
provides details of Beyond the Basics, a similar diet-planning system used in Canada.
Putting the Plan into Action
Familiarizing yourself with each of the food groups is the first step in diet planning.
Table 2-7 shows how to use the USDA Food Guide to plan a 2000-kcalorie diet. The
amounts listed from each of the food groups (see the second column of the table)
were taken from Table 2-3 (p. 41). The next step is to assign the food groups to meals
(and snacks), as in the remaining columns of Table 2-7.
Now, a person can begin to fill in the plan with real foods to create a menu. For
example, the breakfast calls for 1 ounce grain, 1/2 cup fruit, and 1 cup milk. A per-
son might select a bowl of cereal with banana slices and milk:
1 cup cereal = 1 ounce grain
1 small banana = 1/2 cup fruit
1 cup fat-free milk = 1 cup milk
Or 1/2 bagel and a bowl of cantaloupe pieces topped with yogurt:
1/2 small bagel = 1 ounce grain
1/2 cup melon pieces = 1/2 cup fruit
1 cup fat-free plain yogurt = 1 cup milk
Then the person can continue to create a diet plan by creating menus for lunch, din-
ner, and snacks. The final plan might look like the one in Figure 2-4. With the addi-
tion of a small amount of oils, this sample diet plan provides about 1850 kcalories
and adequate amounts of the essential nutrients.
As you can see, we all make countless food-related decisions daily—whether we
have a plan or not. Following a plan, such as the USDA Food Guide, that incorpo-
rates health recommendations and diet-planning principles helps a person make
wise decisions.
From Guidelines to Groceries
Dietary recommendations emphasize nutrient-rich foods such as whole grains,
fruits, vegetables, lean meats, fish, poultry, and low-fat milk products. You can de-
sign such a diet for yourself, but how do you begin? Start with the foods you enjoy
Food Group Amounts Breakfast Lunch Snack Dinner Snack
Fruits 2 c 1
⁄2 c 1
⁄2 c 1 c
Vegetables 21
⁄2 c 1 c 11
⁄2 c
Grains 6 oz 1 oz 2 oz 1
⁄2 oz 2 oz 1
⁄2 oz
Meat and legumes 51
⁄2 oz 2 oz 31
⁄2 oz
Milk 3 c 1 c 1 c 1 c
Oils 51
⁄2 tsp 11
⁄2 tsp 4 tsp
Discretionary kcalorie allowance 267 kcal
This diet plan is one of many possibilities. It follows the amounts of foods suggested for a 2000-kcalorie diet as shown in Table 2-3 on p. 41 (with an extra
1
⁄2 cup of vegetables).
©
Matthew
Farruggio
Most bagels today weigh in at 4 ounces or
more—meaning that a person eating one of
these large bagels for breakfast is actually
getting four or more grain servings, not one.

Amounts Energy (kcal)
8
71
81
425
22
67
49
1/2 c vegetables
1 oz meats
2 tsp oils
1 c salad
1/4 c garbanzo beans
2 tbs oil-based salad
dressing and olives
1/2 c vegetables,
21/2 oz meats,
2 oz enriched grains
1/2 c vegetables
2 tsp oils
1 c fruit
Spaghetti with meat sauce
1/2 c green beans
2 tsp soft margarine
1 c strawberries
Dinner
90
83
1/2 oz enriched grains
1 c milk
3 graham crackers
1 c fat-free milk
Snack
86
74
72
1
/2 oz whole grains
1 c milk
1/2 c fruit
4 whole-wheat,
reduced-fat crackers
11
/2 oz low-fat cheddar cheese
1 small apple
Snack
2 oz whole grains,
2 oz meats
11/2 tsp oils
1 c vegetables
272
75
53
1 turkey sandwich on roll
11/2 tbs low-fat mayonnaise
1 c vegetable juice
Lunch
1 oz whole grains
1 c milk
1/2 c fruit
1 c whole-grain cereal
1 c fat-free milk
1 small banana (sliced)
108
83
105
Breakfast
©
Polara
Studios,
Inc.
©
Quest
©
Polara
Studios,
Inc.
©
Polara
Studios,
Inc.
©
Quest
FIGURE 2-4 A Sample Diet Plan and Menu
This sample menu provides about 1850 kcalories and meets dietary recommendations to provide 45 to 65 percent of its kcalories from car-
bohydrate, 20 to 35 percent from fat, and 10 to 35 percent from protein. Some discretionary kcalories were spent on the fat in the low-fat
cheese and in the sugar added to the graham crackers; about 150 discretionary kcalories remain available in this 2000-kcalorie diet plan.

50 • CHAPTER 2
eating. Then try to make improvements, little by little. When shopping, think of the
food groups, and choose nutrient-dense foods within each group.
Be aware that many of the 50,000 food options available today are processed
foods that have lost valuable nutrients and gained sugar, fat, and salt as they
were transformed from farm-fresh foods to those found in the bags, boxes, and
cans that line grocery-store shelves. Their value in the diet depends on the starting
food and how it was prepared or processed. Sometimes these foods have been for-
tified to improve their nutrient contents.
Grains When shopping for grain products, you will find them described as refined,
enriched, or whole grain. These terms refer to the milling process and the making of
grain products, and they have different nutrition implications (see Figure 2-5). Re-
fined foods may have lost many nutrients during processing; enriched products
may have had some nutrients added back; and whole-grain products may be rich
in fiber and all the nutrients found in the original grain. As such, whole-grain prod-
ucts support good health and should account for at least half of the grains daily.
When it became a common practice to refine the wheat flour used for bread by
milling it and throwing away the bran and the germ, consumers suffered a tragic
loss of many nutrients.4 As a consequence, in the early 1940s Congress passed leg-
islation requiring that all grain products that cross state lines be enriched with iron,
Whole-grain products contain much of the germ and bran, as well
as the endosperm; that is why they are so nutritious.
Refined grain products contain only the
endosperm. Even with nutrients added back,
they are not as nutritious as whole-grain
products, as the next figure shows.
The protective coating of bran around the kernel of
grain is rich in nutrients and fiber.
The endosperm contains starch and proteins.
The germ is the seed that grows into a wheat
plant, so it is especially rich in vitamins and
minerals to support new life.
The outer husk (or chaff) is the inedible part of a grain.
Common types of flour:
• Refined flour—finely ground endosperm that is usually enriched with nutrients
and bleached for whiteness; sometimes called white flour.
• Wheat flour—any flour made from the endosperm of the wheat kernel.
• Whole-wheat flour—any flour made from the entire wheat kernel.
The difference between white flour and white wheat is noteworthy. Typically, white flour refers
to refined flour (as defined above). Most flour—whether refined, white, or whole wheat—is
made from red wheat. Whole-grain products made from red wheat are typically brown and
full flavored.
To capture the health benefits of whole grains for consumers who prefer white bread,
manufacturers have been experimenting with an albino variety of wheat called white wheat.
Whole-grain products made from white wheat provide the nutrients and fiber of a whole
grain with a light color and natural sweetness. Read labels carefully—white bread is a
whole-grain product only if it is made from whole white wheat.
FIGURE 2-5 A Wheat Plant
processed foods: foods that have been
treated to change their physical, chemical,
microbiological, or sensory properties.
fortified: the addition to a food of nutrients
that were either not originally present
or present in insignificant amounts.
Fortification can be used to correct or
prevent a widespread nutrient deficiency
or to balance the total nutrient profile of
a food.
refined: the process by which the coarse
parts of a food are removed. When wheat is
refined into flour, the bran, germ, and husk
are removed, leaving only the endosperm.
enriched: the addition to a food of nutrients
that were lost during processing so that the
food will meet a specified standard.
whole grain: a grain milled in its entirety (all
but the husk), not refined.
©
Thomas
Harm/Tom
Peterson/Quest
Photographic
Inc.

thiamin, riboflavin, and niacin. In 1996, this legislation was amended to include
folate, a vitamin considered essential in the prevention of some birth defects. Most
grain products that have been refined, such as rice, wheat pastas like macaroni
and spaghetti, and cereals (both cooked and ready-to-eat types), have subse-
quently been enriched, ◆ and their labels say so.
Enrichment doesn’t make a slice of bread rich in these added nutrients, but peo-
ple who eat several slices a day obtain significantly more of these nutrients than they
would from unenriched bread. Even though the enrichment of flour helps to prevent
deficiencies of these nutrients, it fails to compensate for losses of many other nutri-
ents and fiber. As Figure 2-6 shows, whole-grain items still outshine the enriched
ones. Only whole-grain flour contains all of the nutritive portions of the grain. Whole-
grain products, such as brown rice or oatmeal, provide more nutrients and fiber and
contain less salt and sugar than flavored, processed rice or sweetened cereals.
Speaking of cereals, ready-to-eat breakfast cereals are the most highly fortified
foods on the market. Like an enriched food, a fortified food has had nutrients added
during processing, but in a fortified food, the added nutrients may not have been
present in the original product. (The terms fortified and enriched may be used inter-
changeably.5) Some breakfast cereals made from refined flour and fortified with
high doses of vitamins and minerals are actually more like supplements disguised
◆ Grain enrichment nutrients:
• Iron
• Thiamin
• Riboflavin
• Niacin
• Folate
10 20 30 40 50 60 70 80 90 100
Iron
Niacin
Thiamin
Riboflavin
Folate
Vitamin B6
Magnesium
Zinc
Fiber
Whole-grain bread
Key:
Enriched bread
Unenriched bread
Percentage of nutrients as compared with whole-grain bread
FIGURE 2-6 Nutrients in Bread
Whole-grain bread is more nutritious than other breads, even enriched bread. For
iron, thiamin, riboflavin, niacin, and folate, enriched bread provides about the
same quantities as whole-grain bread and significantly more than unenriched
bread. For fiber and the other nutrients (those shown here as well as those not
shown), enriched bread provides less than whole-grain bread.
Consume 3 or more ounce-equivalents of whole-grain products per day, with
the rest of the recommended grains coming from enriched or whole-grain
products. In general, at least half the grains should come from whole grains.
When shopping for bread, look for the descrip-
tive words whole grain or whole wheat and
check the fiber contents on the Nutrition Facts
panel of the label—the more fiber, the more
likely the bread is a whole-grain product.
©
Geri
Engberg
Photography

52 • CHAPTER 2
as cereals than they are like whole grains. They may be nutritious—with respect
to the nutrients added—but they still may fail to convey the full spectrum of nu-
trients that a whole-grain food or a mixture of such foods might provide. Still, for-
tified foods help people meet their vitamin and mineral needs.6
Vegetables Posters in the produce section of grocery stores encourage consumers
to “eat 5 a day.” Such efforts are part of a national educational campaign to in-
crease fruit and vegetable consumption to 5 to 9 servings every day (see Figure 2-7).
To help consumers remember to eat a variety of fruits and vegetables, the campaign
provides practical tips, such as selecting from each of five colors.
Choose fresh vegetables often, especially dark green leafy and yellow-orange
vegetables like spinach, broccoli, and sweet potatoes. Cooked or raw, vegetables are
good sources of vitamins, minerals, and fiber. Frozen and canned vegetables with-
out added salt are acceptable alternatives to fresh. To control fat, energy, and
sodium intakes, limit butter and salt on vegetables.
Choose often from the variety of legumes available. ◆ They are an economical,
low-fat, nutrient- and fiber-rich food choice.
Choose a variety of fruits and vegetables each day. In particular, select
from all five vegetable subgroups (dark green, orange, legumes, starchy
vegetables, and other vegetables) several times a week.
◆ Legumes include a variety of beans and peas:
• Adzuki beans • Lentils
• Black beans • Lima beans
• Black-eyed peas • Navy beans
• Fava beans • Peanuts
• Garbanzo beans • Pinto beans
• Great northern beans • Soybeans
• Kidney beans • Split peas
Combining legumes with
foods from other food
groups creates delicious
meals.
Add rice to red beans for a
hearty meal.
Enjoy a Greek salad topped
with garbanzo beans for a
little ethnic diversity.
A bit of meat and lots of
spices turn kidney beans
into chili con carne.
©
1998
Photo
Disc
Inc.
©
Felicia
Martinez
Newman/PhotoEdit
©
Michael
Newman/PhotoEdit
©
1998
Photo
Disc
Inc.
Fruit Choose fresh fruits often, especially citrus fruits and yellow-orange fruits like
cantaloupes and peaches. Frozen, dried, and canned fruits without added sugar are
acceptable alternatives to fresh. Fruits supply valuable vitamins, minerals, fibers,
and phytochemicals. They add flavors, colors, and textures to meals, and their nat-
ural sweetness makes them enjoyable as snacks or desserts.
FIGURE 2-7 Eat 5 to 9 a Day for Better Health
The “5 to 9 a Day” campaign (www.5aday.gov) encourages consumers to eat a variety of fruits and vegetables. Because “everyone
benefits from eating more,” the campaign’s slogan and messages are being revised to say Fruits and Veggies—More Matters.

textured vegetable protein: processed
soybean protein used in vegetarian products
such as soy burgers.
imitation foods: foods that substitute
for and resemble another food, but are
nutritionally inferior to it with respect to
vitamin, mineral, or protein content. If
the substitute is not inferior to the food it
resembles and if its name provides an
accurate description of the product, it
need not be labeled “imitation.”
food substitutes: foods that are designed to
replace other foods.
Consume a sufficient amount of fruits and vegetables while staying
within energy needs.
Fruit juices are healthy beverages but contain little dietary fiber compared with
whole fruits. Whole fruits satisfy the appetite better than juices, thereby helping
people to limit food energy intakes. For people who need extra food energy, though,
juices are a good choice. Be aware that sweetened fruit “drinks” or “ades” contain
mostly water, sugar, and a little juice for flavor. Some may have been fortified with
vitamin C or calcium but lack any other significant nutritional value.
◆ Be aware that not all soy milks have been
fortified. Read labels carefully.
◆ Reminder: Functional foods contain
physiologically active compounds that pro-
vide health benefits beyond basic nutrition.
◆ Milk descriptions:
• Fat-free milk may also be called non-
fat, skim, zero-fat, or no-fat.
• Low-fat milk refers to 1% milk.
• Reduced-fat milk refers to 2% milk;
it may also be called less-fat.
Consume 3 cups per day of fat-free or low-fat milk or equivalent
milk products.
Food group plans such as the USDA Food Guide help consumers select the
types and amounts of foods to provide adequacy, balance, and variety in
the diet. They make it easier to plan a diet that includes a balance of
grains, vegetables, fruits, meats, and milk products. In making any food
choice, remember to view the food in the context of your total diet. The
combination of many different foods provides the abundance of nutrients
that is so essential to a healthy diet.
IN SUMMARY
Meat, Fish, and Poultry Meat, fish, and poultry provide essential minerals, such
as iron and zinc, and abundant B vitamins as well as protein. To buy and prepare
these foods without excess energy, fat, and sodium takes a little knowledge and
planning. When shopping in the meat department, choose fish, poultry, and lean
cuts of beef and pork named “round” or “loin” (as in top round or pork tenderloin).
As a guide, “prime” and “choice” cuts generally have more fat than “select” cuts.
Restaurants usually serve prime cuts. Ground beef, even “lean” ground beef, derives
most of its food energy from fat. Have the butcher trim and grind a lean round steak
instead. Alternatively, textured vegetable protein can be used instead of ground
beef in a casserole, spaghetti sauce, or chili, saving fat kcalories.
Weigh meat after it is cooked and the bones and fat are removed. In general, 4
ounces of raw meat is equal to about 3 ounces of cooked meat. Some examples of
3-ounce portions of meat include 1 medium pork chop, 1/2 chicken breast, or 1
steak or hamburger about the size of a deck of cards. To keep fat intake moderate,
bake, roast, broil, grill, or braise meats (but do not fry them in fat); remove the
skin from poultry after cooking; trim visible fat before cooking; and drain fat after
cooking. Chapter 5 offers many additional strategies for moderating fat intake.
Milk Shoppers find a variety of fortified foods in the dairy case. Examples are milk, to
which vitamins A and D have been added, and soy milk, ◆ to which calcium, vitamin
D, and vitamin B12 have been added. In addition, shoppers may find imitation
foods (such as cheese products), food substitutes (such as egg substitutes), and func-
tional foods ◆ (such as margarine with added plant sterols). As food technology ad-
vances, many such foods offer alternatives to traditional choices that may help people
who want to reduce their fat and cholesterol intakes. Chapter 5 gives other examples.
When shopping, choose fat-free ◆ or low-fat milk, yogurt, and cheeses. Such se-
lections help consumers meet their vitamin and mineral needs within their energy
and fat allowances.7 Milk products are important sources of calcium, but can pro-
vide too much sodium and fat if not selected with care.

54 • CHAPTER 2
Food Labels
Many consumers read food labels to help them make healthy choices.8 Food la-
bels appear on virtually all processed foods, and posters or brochures provide
similar nutrition information for fresh meats, fruits, and vegetables (see Figure
2-8). A few foods need not carry nutrition labels: those contributing few nutri-
ents, such as plain coffee, tea, and spices; those produced by small businesses;
and those prepared and sold in the same establishment. Producers of some of
these items, however, voluntarily use labels. Even markets selling nonpackaged
items voluntarily present nutrient information, either in brochures or on signs
posted at the point of purchase. Restaurants need not supply complete nutri-
tion information for menu items unless claims such as “low fat” or “heart
healthy” have been made. When ordering such items, keep in mind that
restaurants tend to serve extra-large portions—two to three times standard
serving sizes. A “low-fat” ice cream, for example, may have only 3 grams of fat
per 1/2 cup, but you may be served 2 cups for a total of 12 grams of fat and all
their accompanying kcalories.
No Saturated Fat,No Trans Fat
and No Cholesterol
Weston Mills, MapleWood Illinois 00550
Although many factors affect
heart disease, diets low in
saturated fat and cholesterol
may reduce the risk of this disease.
INGREDIENTS, listed in descending order of predominance:
Corn, Sugar, Salt, Malt flavoring, freshness preserved by BHT.
VITAMINS and MINERALS: Vitamin C (Sodium ascorbate),
Niacinamide , Iron, Vitamin B6 (Pyridoxine hydrochloride),
Vitamin B2 (Riboflavin), Vitamin A (Palmitate), Vitamin B1
(Thiamin hydrochloride), Folic acid, and Vitamin D.
Total Fat 1 g 2%
*Percent Daily Values are based on
a 2000 calorie diet. Your daily
values may be higher or lower
depending on your calorie needs.
Serving size 3
/4 cup (28 g)
Servings per container 14
Calories 110
Amount per serving
Calories from fat 9
% Daily Value*
Saturated fat 0 g
Trans fat 0 g
0%
Cholesterol 0 mg 0%
Sodium 250 mg 10%
8%
Protein 3 g
Vitamin A 25% • Vitamin C 25% • Calcium 2% • Iron 25%
2000 2500
Total fat
Sat fat
Cholesterol
Sodium
Total Carbohydrate
Fiber
65 g
20 g
300 mg
2400 mg
300 g
25 g
80 g
25 g
300 mg
2400 mg
375 g
30 g
Less than
Less than
Less than
Less than
Calories:
Calories per gram
Fat 9 • Carbohydrate 4 • Protein 4
6%
Sugars 10 g
Dietary fiber 1.5 g
Total Carbohydrate 23 g
Nutrition Facts
INGRED
IENTS
, listed in de
scen
ding
orde
r of
pred
om
inan
ce
:
Corn,
Su
ga
r, Sa
lt, Malt flavorin
g,
fre
shne
ss
preserved by
BH
T.
VITA
MINS an
d MINER
ALS
: Vitamin C (Sod
ium
asco
rbate),
Niach
am
ide,
Iro
n,
Vitamin B6
(Pyridoxine hydroc
hloride),
Vitamin B2
(Riboflavin), Vitamin A (Palmitate), Vitamin B1
(Thiam
in hydroc
hloride), Fo
lic
ac
id, an
d Vitamin D.
Total Fat 1 g
2%
*Percent Daily Values are based on
a 2000 calorie diet. Your daily
values may be higher or lower
depending on your calorie needs.
Serving size
3/4 cup (28 g)
Servings per container
14
Calories 110
Amount per serving
Calories from Fat 9
% Daily Value*
Saturated fat 0 g
0%
Cholesterol 0 mg
0%
Sodium 250 mg
10%
8%
Protein 3 g
Vitamin A 25% • Vitamin C 25% • Calcium
2%
• Iron 25%
2000
2500
Total fat
Sat fat
Cholesterol
Sodium
Total Carbohydrate
Fiber
65
g
20
g
300 mg
2400
mg
300 g
25
g
80
g
25
g
300 mg
2400
mg
375 g
30
g
Less
than
Less
than
Less
than
Less
than
Calories:
Calories per gram
Fat 9
• Carbohydrate 4
• Protein 4
6%
Sugars 10 g
Dietary fiber 1.5 g
Total Carbohydrate 23 g
Nutrition Facts
The name and
address of the
manufacturer,
packer, or distributor
The common or
usual product
name
Approved nutrient claims
if the product meets
specified criteria
The net contents in
weight, measure,
or count
Approved health claims stated
in terms of the total diet
The serving size and number
of servings per container
kCalorie information and
quantities of nutrients per
serving, in actual amounts
Daily Values reminder for
selected nutrients for a
2000- and a 2500-
kcalorie diet
kCalorie per gram reminder
The ingredients in
descending order of
predominance by weight
Quantities of nutrients as
“% Daily Values” based on a
2000-kcalorie energy intake
FIGURE 2-8 Example of a Food Label

The Ingredient List
All packaged foods must list all ingredients on the label in descending order of pre-
dominance by weight. Knowing that the first ingredient predominates by weight,
consumers can glean much information. Compare these products, for example:
• A beverage powder that contains “sugar, citric acid, natural flavors . . .” ver-
sus a juice that contains “water, tomato concentrate, concentrated juices of
carrots, celery . . .”
• A cereal that contains “puffed milled corn, sugar, corn syrup, molasses, salt
. . .” versus one that contains “100 percent rolled oats”
• A canned fruit that contains “sugar, apples, water” versus one that contains
simply “apples, water”
In each of these comparisons, consumers can see that the second product is the more
nutrient dense.
Serving Sizes
Because labels present nutrient information per serving, they must identify the size of
the serving. The Food and Drug Administration (FDA) has established specific serv-
ing sizes for various foods and requires that all labels for a given product use the
same serving size. For example, the serving size for all ice creams is 1/2 cup and for
all beverages, 8 fluid ounces. This facilitates comparison shopping. Consumers can
see at a glance which brand has more or fewer kcalories or grams of fat, for exam-
ple. Standard serving sizes are expressed in both common household measures,
such as cups, and metric measures, such as milliliters, to accommodate users of both
types of measures (see Table 2-8).
When examining the nutrition facts on a food label, consumers need to compare
the serving size on the label with how much they actually eat and adjust their calcu-
lations accordingly. For example, if the serving size is four cookies and you only eat
two, then you need to cut the nutrient and kcalorie values in half; similarly, if you eat
eight cookies, then you need to double the values. Notice, too, that small bags or in-
dividually wrapped items, such as chips or candy bars, may contain more than a sin-
gle serving. The number of servings per container is listed just below the serving size.
Be aware that serving sizes on food labels are not always the same as those of the
USDA Food Guide.9 For example, a serving of rice on a food label is 1 cup, whereas in
the USDA Food Guide it is 1/2 cup. Unfortunately, this discrepancy, coupled with each
person’s own perception (oftentimes misperception) of standard serving sizes, some-
times creates confusion for consumers trying to follow recommendations.
Nutrition Facts
In addition to the serving size and the servings per container, the FDA requires that
the “Nutrition Facts” panel on food labels present nutrient information in two
ways—in quantities (such as grams) and as percentages of standards called the
Daily Values. The Nutrition Facts panel must provide the nutrient amount, per-
cent Daily Value, or both for the following:
• Total food energy (kcalories)
• Food energy from fat (kcalories)
• Total fat (grams and percent Daily Value)
• Saturated fat (grams and percent Daily Value)
• Trans fat (grams)
• Cholesterol (milligrams and percent Daily Value)
• Sodium (milligrams and percent Daily Value)
Daily Values (DV): reference values
developed by the FDA specifically for
use on food labels.
TABLE 2-8 Household and Metric
Measures
• 1 teaspoon (tsp) 5 milliliters (mL)
• 1 tablespoon (tbs) 15 mL
• 1 cup (c) 240 mL
• 1 fluid ounce (fl oz) 30 mL
• 1 ounce (oz) 28 grams (g)
NOTE: The Aids to Calculation section at the back of the book
provides additional weights and measures.

56 • CHAPTER 2
• Total carbohydrate, which includes starch, sugar, and fiber (grams and per-
cent Daily Value)
• Dietary fiber (grams and percent Daily Value)
• Sugars, which includes both those naturally present in and those added to
the food (grams)
• Protein (grams)
The labels must also present nutrient content information as a percentage of the
Daily Values for the following vitamins and minerals:
• Vitamin A
• Vitamin C
• Iron
• Calcium
The Daily Values
The FDA developed the Daily Values for use on food labels because comparing nu-
trient amounts against a standard helps make the numbers more meaningful to
consumers. Table 2-9 presents the Daily Value standards for nutrients that are re-
quired to provide this information. Food labels list the amount of a nutrient in a
product as a percentage of its Daily Value. A person reading a food label might won-
der, for example, whether 1 milligram of iron or calcium is a little or a lot. As Table
2-9 shows, the Daily Value for iron is 18 milligrams, so 1 milligram of iron is enough
to notice—it is more than 5 percent, and that is what the food label will say. But be-
cause the Daily Value for calcium on food labels is 1000 milligrams, 1 milligram of
calcium is insignificant, and the food label will read “0%.”
The Daily Values reflect dietary recommendations for nutrients and dietary com-
ponents that have important relationships with health. The “% Daily Value” col-
umn on a label provides a ballpark estimate of how individual foods contribute to
the total diet. It compares key nutrients in a serving of food with the goals of a per-
son consuming 2000 kcalories per day. A 2000-kcalorie diet is considered about right
for sedentary younger women, active older women, and sedentary older men.
Consumers read food labels to learn about the
nutrient contents of a food or to compare simi-
lar foods.
TABLE 2-9 Daily Values for Food Labels
Food labels must present the “% Daily Value” for these nutrients.
Food Daily Calculation
Component Value Factors
Fat 65 g 30% of kcalories
Saturated fat 20 g 10% of kcalories
Cholesterol 300 mg —
Carbohydrate (total) 300 g 60% of kcalories
Fiber 25 g 11.5 g per
1000 kcalories
Protein 50 g 10% of kcalories
Sodium 2400 mg —
Potassium 3500 mg —
Vitamin C 60 mg —
Vitamin A 1500 µg —
Calcium 1000 mg —
Iron 18 mg —
NOTE: Daily Values were established for adults and children over 4 years old. The values for energy-yielding nutrients are
based on 2000 kcalories a day. For fiber, the Daily Value was rounded up from 23.
©
Kayte
M.
Deioma/PhotoEdit

◆ % Daily Values:
• 20% = high or excellent source
• 10-19% = good source
• 5% = low
To calculate your personal daily values, log on
to academic.cengage.com/login, then go to
The Daily Values on food labels are
designed for a 2000-kcalorie intake, but
you can calculate a personal set of Daily
Values based on your energy allowance.
Consider a 1500-kcalorie intake, for exam-
ple. To calculate a daily goal for fat, multi-
ply energy intake by 30 percent:
1500 kcal 0.30 kcal from fat
450 kcal from fat
The “kcalories from fat” are listed on food
labels, so you can add all the “kcalories
from fat” values for a day, using 450 as an
upper limit. A person who prefers to count
grams of fat can divide this 450 kcalories
from fat by 9 kcalories per gram to deter-
mine the goal in grams:
450 kcal from fat 9 kcal/g
50 g fat
Alternatively, a person can calculate that
1500 kcalories is 75 percent of the 2000-
kcalorie intake used for Daily
Values:
1500 kcal 2000 kcal 0.75
0.75 100 75%
Then, instead of trying to achieve 100 per-
cent of the Daily Value, a person consum-
ing 1500 kcalories will aim for 75 percent.
Similarly, a person consuming 2800 kcalo-
ries would aim for 140 percent:
2800 kcal 2000 kcal 1.40 or 140%
Table 2-9 includes a calculation column
that can help you estimate your personal
daily value for several nutrients.
HOW TO Calculate Personal Daily Values
Young children and sedentary older women may need fewer kcalories. Most labels
list, at the bottom, Daily Values for both a 2000-kcalorie and a 2500-kcalorie diet,
but the “% Daily Value” column on all labels applies only to a 2000-kcalorie diet. A
2500-kcalorie diet is considered about right for many men, teenage boys, and active
younger women. People who are exceptionally active may have still higher energy
needs. Labels may also provide a reminder of the kcalories in a gram of carbohy-
drate, fat, and protein just below the Daily Value information (review Figure 2-8).
People who consume 2000 kcalories a day can simply add up all of the “%
Daily Values” for a particular nutrient to see if their diet for the day fits recommen-
dations. People who require more or less than 2000 kcalories daily must do some
calculations to see how foods compare with their personal nutrition goals. They
can use the calculation column in Table 2-9 or the suggestions presented in the ac-
companying “How to” feature.
Daily Values help consumers see easily whether a food contributes “a little” or “a
lot” of a nutrient. ◆ For example, the “% Daily Value” column on a label of macaroni
and cheese may say 20 percent for fat. This tells the consumer that each serving of this
food contains about 20 percent of the day’s allotted 65 grams of fat. A person consum-
ing 2000 kcalories a day could simply keep track of the percentages of Daily Values
from foods eaten in a day and try not to exceed 100 percent. Be aware that for some
nutrients (such as fat and sodium) you will want to select foods with a low “% Daily
Value” and for others (such as calcium and fiber) you will want a high “% Daily
Value.” To determine whether a particular food is a wise choice, a consumer needs to
consider its place in the diet among all the other foods eaten during the day.
Daily Values also make it easy to compare foods. For example, a consumer
might discover that frozen macaroni and cheese has a Daily Value for fat of 20 per-
cent, whereas macaroni and cheese prepared from a boxed mix has a Daily Value
of 15 percent. By comparing labels, consumers who are concerned about their fat
intakes can make informed decisions.
The Daily Values used on labels are based in part on values from the 1968 Rec-
ommended Dietary Allowances. Since 1997, Dietary Reference Intakes that reflect
scientific research on diet and health have been released. Efforts to update the Daily
Values based on these current recommendations and to make labels more effective
and easier to understand are underway.10

58 • CHAPTER 2
Nutrient Claims
Have you noticed phrases such as “good source of fiber” on a box of cereal or “rich
in calcium” on a package of cheese? These and other nutrient claims may be
used on labels as long as they meet FDA definitions, which include the conditions
under which each term can be used. For example, in addition to having less than
2 milligrams of cholesterol, a “cholesterol-free” product may not contain more
than 2 grams of saturated fat and trans fat combined per serving. The accompa-
nying glossary defines nutrient terms on food labels, including criteria for foods
described as “low,” “reduced,” and “free.”
Some descriptions imply that a food contains, or does not contain, a nutrient. Im-
plied claims are prohibited unless they meet specified criteria. For example, a claim
that a product “contains no oil” implies that the food contains no fat. If the product
is truly fat-free, then it may make the no-oil claim, but if it contains another source
of fat, such as butter, it may not.
GENERAL TERMS
free: “nutritionally trivial” and
unlikely to have a physiological
consequence; synonyms include
“without,” “no,” and “zero.” A
food that does not contain a
nutrient naturally may make
such a claim, but only as it
applies to all similar foods (for
example, “applesauce, a fat-free
food”).
good source of: the product
provides between 10 and 19%
of the Daily Value for a given
nutrient per serving.
healthy: a food that is low in fat,
saturated fat, cholesterol, and
sodium and that contains at
least 10% of the Daily Values for
vitamin A, vitamin C, iron,
calcium, protein, or fiber.
high: 20% or more of the Daily
Value for a given nutrient per
serving; synonyms include “rich
in” or “excellent source.”
less: at least 25% less of a given
nutrient or kcalories than the
comparison food (see individual
nutrients); synonyms include
“fewer” and “reduced.”
light or lite: one-third fewer
kcalories than the comparison
food; 50% or less of the fat or
sodium than the comparison
food; any use of the term other
than as defined must specify
what it is referring to (for
example, “light in color” or
“light in texture”).
low: an amount that would allow
frequent consumption of a
food without exceeding the
Daily Value for the nutrient. A
food that is naturally low in a
nutrient may make such a
claim, but only as it applies to
all similar foods (for example,
“fresh cauliflower, a low-
sodium food”); synonyms
include “little,” “few,” and
“low source of.”
more: at least 10% more of the
Daily Value for a given nutrient
than the comparison food;
synonyms include “added”
and “extra.”
organic: on food labels, that at
least 95% of the product’s
ingredients have been grown
and processsed according to
USDA regulations defining the
use of fertilizers, herbicides,
insecticides, fungicides,
preservatives, and other
chemical ingredients.
ENERGY
kcalorie-free: fewer than 5 kcal
per serving.
low kcalorie: 40 kcal or less per
serving.
reduced kcalorie: at least 25%
fewer kcalories per serving than
the comparison food.
FAT AND CHOLESTEROLa
percent fat-free: may be used
only if the product meets the
definition of low fat or fat-free
and must reflect the amount of
fat in 100 g (for example, a
food that contains 2.5 g of fat
per 50 g can claim to be “95
percent fat free”).
fat-free: less than 0.5 g of fat per
serving (and no added fat or
oil); synonyms include “zero-
fat,” “no-fat,” and “nonfat.”
low fat: 3 g or less fat per
serving.
less fat: 25% or less fat than the
comparison food.
saturated fat-free: less than 0.5
g of saturated fat and 0.5 g of
trans fat per serving.
low saturated fat: 1 g or less
saturated fat and less than 0.5 g
of trans fat per serving.
less saturated fat: 25% or less
saturated fat and trans fat
combined than the comparison
food.
trans fat-free: less than 0.5 g of
trans fat and less than 0.5 g of
saturated fat per serving.
cholesterol-free: less than 2 mg
cholesterol per serving and 2 g
or less saturated fat and trans fat
combined per serving.
low cholesterol: 20 mg or less
cholesterol per serving and 2 g
or less saturated fat and trans fat
combined per serving.
less cholesterol: 25% or less
cholesterol than the comparison
food (reflecting a reduction of at
least 20 mg per serving), and
2 g or less saturated fat and
trans fat combined per serving.
extra lean: less than 5 g of fat,
2 g of saturated fat and trans
fat combined, and 95 mg of
cholesterol per serving and per
100 g of meat, poultry, and
seafood.
lean: less than 10 g of fat, 4.5 g
of saturated fat and trans fat
combined, and 95 mg of
cholesterol per serving and per
100 g of meat, poultry, and
seafood.
CARBOHYDRATES:
FIBER AND SUGAR
high fiber: 5 g or more fiber per
serving. A high-fiber claim made
on a food that contains more
than 3 g fat per serving and per
100 g of food must also declare
total fat.
sugar-free: less than 0.5 g of
sugar per serving.
SODIUM
sodium-free and salt-free: less
than 5 mg of sodium per
serving.
low sodium: 140 mg or less per
serving.
very low sodium: 35 mg or less
per serving.
aFoods containing more than 13 grams total fat
per serving or per 50 grams of food must
GLOSSARY OF TERMS ON FOOD LABELS
indicate those contents immediately after a cholesterol claim. As you can see, all cholesterol claims are prohibited when the food contains more than 2 grams saturated fat and trans fat combined per serving.
nutrient claims: statements that
characterize the quantity of a nutrient
in a food.

Health Claims
Until 2003, the FDA held manufacturers to the highest standards of scientific evi-
dence before approving health claims on food labels. Consumers reading “Diets
low in sodium may reduce the risk of high blood pressure,” for example, knew
that the FDA had examined enough scientific evidence to establish a clear link be-
tween diet and health. Such reliable health claims make up the FDA’s “A” list (see
Table 2-10). The FDA refers to these health claims as “unqualified”—not that they
lack the necessary qualifications, but that they can stand alone without further
explanation or qualification.
These reliable health claims still appear on some food labels, but finding them
may be difficult now that the FDA has created three additional categories of claims
based on scientific evidence that is less conclusive (see Table 2-11). These categories
were added after a court ruled: “Holding only the highest scientific standard for
claims interferes with commercial free speech.” Food manufacturers had argued
that they should be allowed to inform consumers about possible benefits based on
less than clear and convincing evidence. The FDA must allow manufacturers to
provide information about nutrients and foods that show preliminary promise in
preventing disease. These health claims are “qualified”—not that they meet the
necessary qualifications, but that they require a qualifying explanation. For exam-
ple, “Very limited and preliminary research suggests that eating one-half to one
cup of tomatoes and/or tomato sauce a week may reduce the risk of prostate can-
cer. FDA concludes that there is little scientific evidence supporting the claim.” Con-
sumer groups argue that such information is confusing. Even with required
disclaimers for health claims graded “B,” “C,” or “D,” distinguishing “A” claims
from others is difficult, as the next section shows. (Health claims on supplement la-
bels are presented in Highlight 10.)
Structure-Function Claims
Unlike health claims, which require food manufacturers to collect scientific evidence
and petition the FDA, structure-function claims can be made without any FDA
approval. Product labels can claim to “slow aging,” “improve memory,” and “build
strong bones” without any proof. The only criterion for a structure-function claim is
that it must not mention a disease or symptom. Unfortunately, structure-function
claims can be deceptively similar to health claims. Consider these statements:
• “May reduce the risk of heart disease.”
• “Promotes a healthy heart.”
Most consumers do not distinguish between these two types of claims.11 In the state-
ments above, for example, the first is a health claim that requires FDA approval and
the second is an unproven, but legal, structure-function claim. Table 2-12 lists ex-
amples of structure-function claims.
TABLE 2-10 Food Label Health
Claims—The “A” List
• Calcium and reduced risk of osteoporosis
• Sodium and reduced risk of hypertension
• Dietary saturated fat and cholesterol and
reduced risk of coronary heart disease
• Dietary fat and reduced risk of cancer
• Fiber-containing grain products, fruits, and
vegetables and reduced risk of cancer
• Fruits, vegetables, and grain products that
contain fiber, particularly soluble fiber, and
reduced risk of coronary heart disease
• Fruits and vegetables and reduced risk of
cancer
• Folate and reduced risk of neural tube defects
• Sugar alcohols and reduced risk of tooth decay
• Soluble fiber from whole oats and from psyl-
lium seed husk and reduced risk of heart
disease
• Soy protein and reduced risk of heart disease
• Whole grains and reduced risk of heart disease
and certain cancers
• Plant sterol and plant stanol esters and heart
disease
• Potassium and reduced risk of hypertension
and stroke
TABLE 2-11 The FDA’s Health Claims Report Card
Grade Level of Confidence in Health Claim Required Label Disclaimers
A High: Significant scientific agreement These health claims do not require disclaimers; see Table 2-10 for
examples.
B Moderate: Evidence is supportive but not conclusive “[Health claim.] Although there is scientific evidence supporting this
claim, the evidence is not conclusive.”
C Low: Evidence is limited and not conclusive “Some scientific evidence suggests [health claim]. However, FDA has
determined that this evidence is limited and not conclusive.”
D Very low: Little scientific evidence supporting this claim “Very limited and preliminary scientific research suggests [health claim]. FDA
concludes that there is little scientific evidence supporting this claim.”
health claims: statements that characterize
the relationship between a nutrient or other
substance in a food and a disease or health-
related condition.
structure-function claims: statements that
characterize the relationship between a
nutrient or other substance in a food and
its role in the body.

60 • CHAPTER 2
Consumer Education
Because labels are valuable only if people know how to use them, the FDA has de-
signed several programs to educate consumers. Consumers who understand how to
read labels are best able to apply the information to achieve and maintain health-
ful dietary practices.
Table 2-13 shows how the messages from the 2005 Dietary Guidelines, the USDA
Food Guide, and food labels coordinate with each other. To promote healthy eating
and physical activity, the “Healthier US Initiative” coordinates the efforts of national
educational programs developed by government agencies.12 The mission of this ini-
tiative is to deliver simple messages that will motivate consumers to make small
changes in their eating and physical activity habits to yield big rewards.
• Builds strong bones • Defends your health
• Promotes relaxation • Slows aging
• Improves memory • Guards against colds
• Boosts the immune • Lifts your spirits
system
• Supports heart health
NOTE: Structure-function claims cannot make statements about
diseases. See Table 2-10 on p. 59 for examples of health claims.
TABLE 2-12 Examples of Structure-
Function Claims
TABLE 2-13 From Guidelines to Groceries
Dietary Guidelines USDA Food Guide/MyPyramid Food Labels
Adequate nutrients within Select the recommended amounts from Look for foods that describe their vitamin, mineral, or fiber
energy needs each food group at the energy level contents as a good source or high.
appropriate for your energy needs.
Weight management Select nutrient-dense foods and beverages Look for foods that describe their kcalorie contents as free,
within and among the food groups. low, reduced, light, or less.
Limit high-fat foods and foods and
beverages with added fats and sugars.
Use appropriate portion sizes.
Physical activity Be phyisically active for at least 30 minutes
most days of the week.
Children and teenagers should be physically
active for 60 minutes every day, or most days.
Food groups to encourage Select a variety of fruits each day. Look for foods that describe their fiber contents as good source or high.
Include vegetables from all five subgroups Look for foods that provide at least 10% of the Daily Value
(dark green, orange, legumes, starchy for fiber, vitamin A, vitamin C, iron, and calcium from a
vegetables, and other vegetables) several variety of sources.
times a week.
Make at least half of the grain selections
whole grains.
Select fat-free or low-fat milk products.
Fats Choose foods within each group that are Look for foods that describe their fat, saturated fat, trans fat, and
lean, low fat, or fat-free. cholesterol contents as free, less, low, light, reduced, lean, or extra lean.
Choose foods within each group that have Look for foods that provide no more than 5% of the Daily Value
little added fat. for fat, saturated fat, and cholesterol.
Carbohydrates Choose fiber-rich fruits, vegetables, and Look for foods that describe their sugar contents as free or
whole grains often. reduced.
Choose foods and beverages within each A food may be high in sugar if its ingredients list begins with
group that have little added sugars. or contains several of the following: sugar, sucrose, fructose,
maltose, lactose, honey, syrup, corn syrup, high-fructose corn
syrup, molasses, evaporated cane juice, or fruit juice concentrate.
Sodium and potassium Choose foods within each group that are Look for foods that describe their salt and sodium contents as
low in salt or sodium. free, low, or reduced.
Choose potassium-rich foods such as Look for foods that provide no more than 5% of the Daily
fruits and vegetables. Value for sodium.
Look for foods that provide at least 10% of the Daily Value
for potassium.
Alcoholic beverages Use sensibly and in moderation (no more Light beverages contain fewer kcalories and less alcohol than
than one drink a day for women and regular versions.
two drinks a day for men).
Food safety Follow the safe handling instructions on packages of meat and
other safety instructions, such as keep refrigerated, on packages
of perishable foods.

The secret to making healthy food choices is learning to incorporate the 2005 Dietary
Guidelines and the USDA Food Guide into your decision-making process.
■ Compare the foods you typically eat daily with the USDA Food Guide recom-
mendations for your energy needs (see Table 2-3 on p. 41 and Table 2-4 on
p. 44), making note of which food groups are usually over- or underrepresented.
■ Describe your choices within each food group from day to day and include
realistic suggestions for enhancing the variety in your diet.
■ Write yourself a letter describing the dietary changes you can make to improve
your chances of enjoying good health.
Nutrition Portfolio academic.cengage.com/login
Food labels provide consumers with information they need to select foods that
will help them meet their nutrition and health goals. When labels contain rel-
evant information presented in a standardized, easy-to-read format, con-
sumers are well prepared to plan and create healthful diets.
IN SUMMARY
This chapter provides the links to go from dietary guidelines to buying groceries and
offers helpful tips for selecting nutritious foods. For information on foodborne ill-
nesses, turn to Highlight 18.
• Search for “diet” and “food labels” at the U.S. Government
health information site: www.healthfinder.gov
• Learn more about the Dietary Guidelines for Americans:
www.healthierus.gov/dietaryguidelines
• Find Canadian information on nutrition guidelines and
food labels at: www.hc-sc.gc.ca
• Learn more about the USDA Food Guide and MyPyramid:
mypyramid.gov
• Visit the USDA Food Guide section (including its ethnic/
cultural pyramids) of the U.S. Department of Agriculture:
www.nal.usda.gov/fnic
• Visit the Traditional Diet Pyramids for various ethnic groups
at Oldways Preservation and Exchange Trust:
www.oldwayspt.org
• Search for “exchange lists” at the American Diabetes Associ-
ation: www.diabetes.org
• Learn more about food labeling from the Food and Drug
Administration: www.cfsan.fda.gov
• Search for “food labels” at the International Food
Information Council: www.ific.org
• Assess your diet at the CNPP Interactive Healthy Eating
Index: www.usda.gov/cnpp
• Get healthy eating tips from the “5 a day” programs:
www.5aday.gov or www.5aday.org
These problems will give you practice in doing simple
nutrition-related calculations. Although the situations are
hypothetical, the numbers are real, and calculating the an-
For additional practice log on to academic.cengage.com/login. Go to Chapter 2, then to Nutrition Calculations.
swers (check them on p. 63) provides a valuable nutrition
lesson. Be sure to show your calculations for each problem.

62 • CHAPTER 2
1. Read a food label. Look at the cereal label in Figure 2-8 and
answer the following questions:
a. What is the size of a serving of cereal?
b. How many kcalories are in a serving?
c. How much fat is in a serving?
d. How many kcalories does this represent?
e. What percentage of the kcalories in this product
comes from fat?
f. What does this tell you?
g. What is the % Daily Value for fat?
h. What does this tell you?
i. Does this cereal meet the criteria for a low-fat prod-
uct (refer to the glossary on p. 58)?
j. How much fiber is in a serving?
k. Read the Daily Value chart on the lower section of
the label. What is the Daily Value for fiber?
l. What percentage of the Daily Value for fiber does a
serving of the cereal contribute? Show the calcula-
tion the label-makers used to come up with the %
Daily Value for fiber.
m.What is the predominant ingredient in the cereal?
n. Have any nutrients been added to this cereal (is it
fortified)?
2. Calculate a personal Daily Value. The Daily Values on food
labels are for people with a 2000-kcalorie intake.
a. Suppose a person has a 1600-kcalorie energy
allowance. Use the calculation factors listed in Table
2-9 to calculate a set of personal “Daily Values”
based on 1600 kcalories. Show your calculations.
b. Revise the % Daily Value chart of the cereal label in
Figure 2-8 based on your “Daily Values” for a 1600-
kcalorie diet.
1. Name the diet-planning principles and briefly describe
how each principle helps in diet planning. (pp. 37–39)
2. What recommendations appear in the Dietary Guidelines
for Americans? (pp. 39–40)
3. Name the five food groups in the USDA Food Guide and
identify several foods typical of each group. Explain how
such plans group foods and what diet-planning princi-
ples the plans best accommodate. How are food group
plans used, and what are some of their strengths and
weaknesses? (pp. 41–47)
4. Review the Dietary Guidelines. What types of grocery
selections would you make to achieve those recommen-
dations? (pp. 40, 48–53)
5. What information can you expect to find on a food label?
How can this information help you choose between two
similar products? (pp. 54–57)
6. What are the Daily Values? How can they help you meet
health recommendations? (pp. 55–57)
7. Describe the differences between nutrient claims, health
claims, and structure-function claims. (pp. 58–59)
1. The diet-planning principle that provides all the essen-
tial nutrients in sufficient amounts to support health is:
a. balance.
b. variety.
c. adequacy.
d. moderation.
2. A person who chooses a chicken leg that provides 0.5
milligram of iron and 95 kcalories instead of two table-
spoons of peanut butter that also provide 0.5 milligram of
iron but 188 kcalories is using the principle of nutrient:
a. control.
b. density.
c. adequacy.
d. moderation.
3. Which of the following is consistent with the Dietary
Guidelines for Americans?
a. Choose a diet restricted in fat and cholesterol.
b. Balance the food you eat with physical activity.
c. Choose a diet with plenty of milk products and meats.
d. Eat an abundance of foods to ensure nutrient
adequacy.
4. According to the USDA Food Guide, added fats and sug-
ars are counted as:
a. meats and grains.
b. nutrient-dense foods.
c. discretionary kcalories.
d. oils and carbohydrates.
5. Foods within a given food group of the USDA Food
Guide are similar in their contents of:
a. energy.
b. proteins and fibers.
c. vitamins and minerals.
d. carbohydrates and fats.
6. In the exchange system, each portion of food on any
given list provides about the same amount of:
a. energy.
b. satiety.
c. vitamins.
d. minerals.
7. Enriched grain products are fortified with:
a. fiber, folate, iron, niacin, and zinc.
b. thiamin, iron, calcium, zinc, and sodium.
c. iron, thiamin, riboflavin, niacin, and folate.
d. folate, magnesium, vitamin B6, zinc, and fiber.
STUDY QUESTIONS

1. S. P. Murphy and coauthors, Simple measures
of dietary variety are associated with im-
proved dietary quality, Journal of the American
Dietetic Association 106 (2006): 425–429.
2. U.S. Department of Agriculture and U.S.
Department of Health and Human Services,
Dietary Guidelines for Americans, 2005, available
at www.healthierus.gov/dietaryguidelines.
3. Position of the American Dietetic Association
and Dietitians of Canada: Vegetarian diets,
Journal of the American Dietetic Association 103
(2003): 748–765.
4. J. R. Backstrand, The history and future of
food fortification in the United States: A
public health perspective, Nutrition Reviews 60
(2002): 15–26.
5. As cited in 21 Code of Federal Regulations—
Food and Drugs, Section 104.20, 45 Federal
Register 6323, January 25, 1980, as amended
in 58 Federal Register 2228, January 6, 1993.
6. Position of the American Dietetic Association:
Food fortification and nutritional supple-
ments, Journal of the American Dietetic Associa-
tion 105 (2005): 1300–1311.
7. R. Ranganathan and coauthors, The nutri-
tional impact of dairy product consumption
on dietary intakes of adults (1995–1996): The
Bogalusa Heart Study, Journal of the American
Dietetic Association 105 (2005): 1391–1400; L.
G. Weinberg, L. A. Berner, and J. E. Groves,
Nutrient contributions of dairy foods in the
United States, Continuing Survey of Food
Intakes by Individuals, 1994–1996, 1998,
(2004): 895–902.
8. L. LeGault and coauthors, 2000–2001 Food
Label and Package Survey: An update on
prevalence of nutrition labeling and claims
on processed, packaged foods, Journal of the
952–958.
9. D. Herring and coauthors, Serving sizes in the
Food Guide Pyramid and on the nutrition
facts label: What’s different and why? Family
Economics and Nutrition Review 14 (2002):
71–73.
10. Dietary Reference Intakes (DRIs) for food
labeling, American Journal of Clinical Nutrition
83 (2006): suppl; T. Philipson, Government
perspective: Food labeling, American Journal of
Clinical Nutrition 82 (2005): 262S–264S; The
National Academy of Sciences, Dietary Refer-
ence Intakes: Guiding principles for nutrition
labeling and fortification (2004),
http://www.nap.edu/openbook/0309091438/
html/R1.html.
11. P. Williams, Consumer understanding and
use of health claims for foods, Nutrition Re-
views 63 (2005): 256–264.
12. K. A. Donato, National health education
programs to promote healthy eating and
physical activity, Nutrition Reviews 64 (2006):
S65–S70.
REFERENCES
8. Food labels list ingredients in:
a. alphabetical order.
b. ascending order of predominance by weight.
c. descending order of predominance by weight.
d. manufacturer’s order of preference.
9. “Milk builds strong bones” is an example of a:
a. health claim.
b. nutrition fact.
c. nutrient content claim.
d. structure-function claim.
10. Daily Values on food labels are based on a:
a. 1500-kcalorie diet.
b. 2000-kcalorie diet.
c. 2500-kcalorie diet.
d. 3000-kcalorie diet.
1. a. 3
⁄4 cup (28 g)
b. 110 kcalories
c. 1 g fat
d. 9 kcalories
e. 9 kcal 110 kcal 0.08
0.08 100 8%
f. This cereal derives 8 percent of its kcalories from fat
g. 2%
h. A serving of this cereal provides 2 percent of the 65 grams
of fat recommended for a 2000-kcalorie diet
i. Yes
j. 1.5 g fiber
k. 25 g
l. 1.5 g 25 g 0.06
0.06 100 6%
m. Corn
n. Yes
2. a. Daily Values for 1600-kcalorie diet:
Fat: 1600 kcal 0.30 480 kcal from fat
480 kcal 9 kcal/g 53 g fat
Saturated fat: 1600 kcal 0.10 160 kcal from saturated fat
160 kcal 9 kcal/g 18 g saturated fat
Cholesterol: 300 mg
Carbohydrate: 1600 kcal 0.60 960 kcal from carbohydrate
960 kcal 4 kcal/g 240 g carbohydrate
Fiber: 1600 kcal 1000 kcal 1.6
1.6 11.5 g 18.4 g fiber
Protein: 1600 kcal 0.10 160 kcal from protein
160 kcal 4 kcal/g 40 g protein
Sodium: 2400 mg
Potassium: 3500 mg
b.
Total fat 2% (1 g 53 g)
Saturated fat 0% (0 g 18 g)
Cholesterol 0% (no calculation needed)
Sodium 10% (no calculation needed)
Total carbohydrate 10% (23 g 240 g)
Dietary fiber 8% (1.5 g 18.4 g)
1. c 2. b 3. b 4. c 5. c 6. a 7. c 8. c
9. d 10. b
ANSWERS

HIGHLIGHT 2
Vegetarian Diets
64
The waiter presents this evening’s specials: a
fresh spinach salad topped with mandarin
oranges, raisins, and sunflower seeds, served
with a bowl of pasta smothered in a mush-
room and tomato sauce and topped with
grated parmesan cheese. Then this one: a
salad made of chopped parsley, scallions, cel-
ery, and tomatoes mixed with bulgur wheat
and dressed with olive oil and lemon juice, served with a spinach
and feta cheese pie. Do these meals sound good to you? Or is
something missing . . . a pork chop or ribeye, perhaps?
Would vegetarian fare be acceptable to you some of the time?
Most of the time? Ever? Perhaps it is helpful to recognize that di-
etary choices fall along a continuum—from one end, where peo-
ple eat no meat or foods of animal origin, to the other end, where
they eat generous quantities daily. Meat’s place in the diet has
been the subject of much research and controversy, as this high-
light will reveal. One of the missions of this highlight, in fact, is to
identify the range of meat intakes most compatible with health.
The health benefits of a primarily vegetarian diet seem to have
encouraged many people to eat more vegetarian meals. The pop-
ular press refers to these “part-time vegetarians” who eat small
amounts of meat from time to time as “flexitarians.”
People who choose to exclude meat and other animal-de-
rived foods from their diets today do so for many of the same
reasons the Greek philosopher Pythagoras cited in the sixth
century B.C.: physical health, ecological responsibility, and
philosophical concerns. They might also cite
world hunger issues, economic reasons, eth-
ical concerns, or religious beliefs as motivat-
ing factors. Whatever their reasons—and
even if they don’t have a particular reason—
people who exclude meat will be better pre-
pared to plan well-balanced meals if they
understand the nutrition and health implica-
tions of vegetarian diets.
Vegetarians generally are categorized, not by their motiva-
tions, but by the foods they choose to exclude (see the glossary
below). Some people exclude red meat only; some also exclude
chicken or fish; others also exclude eggs; and still others exclude
milk and milk products as well. In fact, finding agreement on the
definition of the term vegetarian is a challenge.1
As you will see, though, the foods a person excludes are not
nearly as important as the foods a person includes in the diet. Veg-
etarian diets that include a variety of whole grains, vegetables,
legumes, nuts, and fruits offer abundant complex carbohydrates
and fibers, an assortment of vitamins and minerals, a mixture of
phytochemicals, and little fat—characteristics that reflect current
dietary recommendations aimed at promoting health and reduc-
ing obesity. Each of these foods—whole grains, vegetables,
legumes, nuts, and fruits—independently reduces the risk for sev-
eral chronic diseases.2 This highlight examines the health benefits
and potential problems of vegetarian diets and shows how to
plan a well-balanced vegetarian diet.
lactovegetarians: people who
include milk and milk products,
but exclude meat, poultry, fish,
seafood, and eggs from their
diets.
• lacto milk
lacto-ovo-vegetarians: people
who include milk, milk
products, and eggs, but exclude
meat, poultry, fish, and seafood
from their diets.
• ovo egg
macrobiotic diets: extremely
restrictive diets limited to a few
grains and vegetables; based on
metaphysical beliefs and not on
nutrition. A macrobiotic diet
might consist of brown rice,
miso soup, and sea vegetables,
for example.
meat replacements: products
formulated to look and taste like
meat, fish, or poultry; usually
made of textured vegetable
protein.
omnivores: people who have no
formal restriction on the eating
of any foods.
• omni all
• vores to eat
tempeh (TEM-pay): a fermented
soybean food, rich in protein
and fiber.
textured vegetable protein:
processed soybean protein used
in vegetarian products such as
soy burgers; see also meat
replacements.
tofu (TOE-foo): a curd made from
soybeans, rich in protein and
often fortified with calcium; used
in many Asian and vegetarian
dishes in place of meat.
vegans (VEE-gans): people who
exclude all animal-derived foods
(including meat, poultry, fish,
eggs, and dairy products) from
their diets; also called pure
vegetarians, strict vegetarians,
or total vegetarians.
vegetarians: a general term used
to describe people who exclude
meat, poultry, fish, or other
animal-derived foods from
their diets.
GLOSSARY
©
Polora
Studios,
Inc.

Health Benefits of Vegetarian
Diets
Research on the health implications of vegetarian diets would be
relatively easy if vegetarians differed from other people only in
not eating meat. Many vegetarians, however, have also adopted
lifestyles that may differ from many omnivores: they typically
use no tobacco or illicit drugs, use little (if any) alcohol, and are
physically active. Researchers must account for these lifestyle dif-
ferences before they can determine which aspects of health cor-
relate just with diet. Even then, correlations merely reveal what
health factors go with the vegetarian diet, not what health effects
may be caused by the diet. Despite these limitations, research
findings suggest that well-planned vegetarian diets offer sound
nutrition and health benefits to adults.3 Dietary patterns that in-
clude very little, if any, meat may even increase life expectancy.4
Weight Control
In general, vegetarians maintain a lower and healthier body
weight than nonvegetarians.5 Vegetarians’ lower body weights
correlate with their high intakes of fiber and low intakes of fat. Be-
cause obesity impairs health in a number of ways, this gives veg-
etarians a health advantage.
Blood Pressure
Vegetarians tend to have lower blood pressure and lower rates of
hypertension than nonvegetarians. Appropriate body weight helps
to maintain a healthy blood pressure, as does a diet low in total fat
and saturated fat and high in fiber, fruits, vegetables, and soy pro-
tein.6 Lifestyle factors also influence blood pressure: smoking and
alcohol intake raise blood pressure, and physical activity lowers it.
Heart Disease
The incidence of heart disease and related deaths is much lower
for vegetarians than for meat eaters. The dietary factor most di-
rectly related to heart disease is saturated animal fat, and in gen-
eral, vegetarian diets are lower in total fat, saturated fat, and
cholesterol than typical meat-based diets.7 The fats common in
plant-based diets—the monounsaturated fats of olives, seeds, and
nuts and the polyunsaturated fats of vegetable oils—are associ-
ated with a decreased risk of heart disease.8 Furthermore, vege-
tarian diets are generally higher in dietary fiber, antioxidant
vitamins, and phytochemicals—all factors that help control blood
lipids and protect against heart disease.9
Many vegetarians include soy products such as tofu in their
diets. Soy products may help to protect against heart disease be-
cause they contain polyunsaturated fats, fiber, vitamins, and min-
erals, and little saturated fat.10 Even when intakes of energy,
protein, carbohydrate, total fat, saturated fat, unsaturated fat, al-
cohol, and fiber are the same, people eating meals based on tofu
have lower blood cholesterol and triglyceride levels than those
eating meat. Some research suggests that soy protein and phyto-
chemicals may be responsible for some of these health benefits
(as Highlight 13 explains in greater detail).11
Cancer
Vegetarians have a significantly lower rate of cancer than the gen-
eral population. Their low cancer rates may be due to their high
intakes of fruits and vegetables (as Highlight 11 explains). In fact,
the ratio of vegetables to meat may be the most relevant dietary
factor responsible for cancer prevention.12
Some scientific findings indicate that vegetarian diets are asso-
ciated not only with lower cancer mortality in general, but also
with lower incidence of cancer at specific sites as well, most no-
tably, colon cancer.13 People with colon cancer seem to eat more
meat, more saturated fat, and fewer vegetables than do people
without colon cancer. High-protein, high-fat, low-fiber diets cre-
ate an environment in the colon that promotes the development
of cancer in some people. A high-meat diet has been associated
with stomach cancer as well.14
Other Diseases
In addition to obesity, hypertension, heart disease, and cancer,
vegetarian diets may help prevent diabetes, osteoporosis, diver-
ticular disease, gallstones, and rheumatoid arthritis.15 These
health benefits of a vegetarian diet depend on wise diet planning.
Vegetarian Diet Planning
The vegetarian has the same meal-planning task as any other per-
son—using a variety of foods to deliver all the needed nutrients
within an energy allowance that maintains a healthy body weight
(as discussed in Chapter 2). Vegetarians who include milk prod-
ucts and eggs can meet recommendations for most nutrients
about as easily as nonvegetarians. Such diets provide enough en-
ergy, protein, and other nutrients to support the health of adults
and the growth of children and adolescents.
Vegetarians who exclude milk products and eggs can select
legumes, nuts, and seeds and products made from them, such as
peanut butter, tempeh, and tofu, from the meat group. Those
who do not use milk can use soy “milk”—a product made from
soybeans that provides similar nutrients if fortified with calcium,
vitamin D, and vitamin B12.
The MyPyramid resources include tips for planning vegetarian
diets using the USDA Food Guide. In addition, several food guides
have been developed specifically for vegetarian diets.16 They all
address the particular nutrition concerns of vegetarians, but differ
slightly. Figure H2-1 presents one version. When selecting from
the vegetable and fruit groups, vegetarians should emphasize
particularly good sources of calcium and iron, respectively. Green
leafy vegetables, for example, provide almost five times as much
calcium per serving as other vegetables. Similarly, dried fruits de-
serve special notice in the fruit group because they deliver six
VEGETARIAN DIETS • 65

times as much iron as other fruits. The milk group features forti-
fied soy milks for those who do not use milk, cheese, or yogurt.
The meat group is called “proteins” and includes legumes, soy
products, nuts, and seeds. A group for oils encourages the use of
vegetable oils, nuts, and seeds rich in unsaturated fats and
omega-3 fatty acids. To ensure adequate intakes of vitamin B12,
vitamin D, and calcium, vegetarians need to select fortified foods
or take supplements daily. The vegetarian food pyramid is flexible
enough that a variety of people can use it: people who have
adopted various vegetarian diets, those who want to make the
transition to a vegetarian diet, and those who simply want to in-
clude more plant-based meals in their diet. Like MyPyramid, this
vegetarian food pyramid also encourages physical activity.
Most vegetarians easily obtain large quantities of the nutrients
that are abundant in plant foods: thiamin, folate, and vitamins B6, C,
A, and E. Vegetarian food guides help to ensure adequate intakes of
the main nutrients vegetarian diets might otherwise lack: protein,
iron, zinc, calcium, vitamin B12, vitamin D, and omega-3 fatty acids.
Protein
The protein RDA for vegetarians is the same as for others, although
some have suggested that it should be higher because of the lower di-
gestibility of plant proteins.17 Lacto-ovo-vegetarians, who use an-
imal-derived foods such as milk and eggs, receive high-quality
proteins and are likely to meet their protein needs. Even those
who adopt only plant-based diets are likely to
meet protein needs provided that their en-
ergy intakes are adequate and the protein
sources varied.18 The proteins of whole
grains, legumes, seeds, nuts, and vegetables
can provide adequate amounts of all the
amino acids. An advantage of many vegetar-
ian sources of protein is that they are gener-
ally lower in saturated fat than meats and are
often higher in fiber and richer in some vita-
mins and minerals.
Vegetarians sometimes use meat replace-
ments made of textured vegetable pro-
tein (soy protein). These foods are formulated
to look and taste like meat, fish, or poultry.
Many of these products are fortified to provide
the vitamins and minerals found in animal
sources of protein. A wise vegetarian learns to
use a variety of whole, unrefined foods often
and commercially prepared foods less fre-
quently. Vegetarians may also use soy prod-
ucts such as tofu to bolster protein intake.
Iron
Getting enough iron can be a problem even
for meat eaters, and those who eat no meat
must pay special attention to their iron in-
take. The iron in plant foods such as legumes,
dark green leafy vegetables, iron-fortified ce-
reals, and whole-grain breads and cereals is
poorly absorbed.19 Because iron absorption from a vegetarian
diet is low, the iron RDA for vegetarians is higher than for others
(see Chapter 13 for more details).
Fortunately, the body seems to adapt to a vegetarian diet by
absorbing iron more efficiently. Furthermore, iron absorption is
enhanced by vitamin C, and vegetarians typically eat many vita-
min C–rich fruits and vegetables. Consequently, vegetarians suf-
fer no more iron deficiency than other people do.20
Zinc
Zinc is similar to iron in that meat is its richest food source, and
zinc from plant sources is not well absorbed.21 In addition, soy,
which is commonly used as a meat alternative in vegetarian
meals, interferes with zinc absorption. Nevertheless, most vege-
tarian adults are not zinc deficient. Perhaps the best advice to
vegetarians regarding zinc is to eat a variety of nutrient-dense
foods; include whole grains, nuts, and legumes such as black-
eyed peas, pinto beans, and kidney beans; and maintain an ade-
quate energy intake. For those who include seafood in their diets,
oysters, crabmeat, and shrimp are rich in zinc.
Calcium
The calcium intakes of lactovegetarians are similar to those of
the general population, but people who use no milk products risk
66 • Highlight 2
Review Figure 2–1 and Table 2–3 to find recommended daily amounts from each
food group, serving size equivalents, examples of common foods within each
group, and the most notable nutrients for each group. Tips for planning a vege-
tarian diet can be found at MyPyramid.gov.
SOURCE: © GC Nutrition Council, 2006, adapted from USDA 2005 Dietary Guidelines and www.mypyramid.gov. Copies can
be ordered from 301-680-6717.
FIGURE H2-1 An Example of a Vegetarian Food Pyramid

deficiency. Careful planners select calcium-rich foods, such as cal-
cium-fortified juices, soy milk, and breakfast cereals, in ample
quantities regularly. This advice is especially important for chil-
dren and adolescents. Soy formulas for infants are fortified with
calcium and can be used in cooking, even for adults. Other good
calcium sources include figs, some legumes, some green vegeta-
bles such as broccoli and turnip greens, some nuts such as al-
monds, certain seeds such as sesame seeds, and calcium-set
tofu.* The choices should be varied because calcium absorption
from some plant foods may be limited (as Chapter 12 explains).
Vitamin B12
The requirement for vitamin B12 is small, but this vitamin is
found only in animal-derived foods. Consequently, vegetarians,
in general, and vegans who eat no foods of animal original, in
particular, may not get enough vitamin B12 in their diets.22 Fer-
mented soy products such as tempeh may contain some vita-
min B12 from the bacteria, but unfortunately, much of the vitamin
B12 found in these products may be an inactive form. Seaweeds
such as nori and chlorella supply some vitamin B12, but not much,
and excessive intakes of these foods can lead to iodine toxicity. To
defend against vitamin B12 deficiency, vegans must rely on vita-
min B12–fortified sources (such as soy milk or breakfast cereals) or
supplements. Without vitamin B12, the nerves suffer damage,
leading to such health consequences as loss of vision.
Vitamin D
People who do not use vitamin D–fortified foods and do not receive
enough exposure to sunlight to synthesize adequate vitamin D may
need supplements to defend against bone loss. This is particularly
important for infants, children, and older adults. In northern cli-
mates during winter months, young children on vegan diets can
readily develop rickets, the vitamin D–deficiency disease.
Omega-3 Fatty Acids
Both Chapter 5 and Highlight 5 describe the health benefits of
unsaturated fats, most notably the omega-3 fatty acids com-
monly found in fatty fish. To obtain sufficient amounts of omega-
3 fatty acids, vegetarians need to consume flaxseed, walnuts, soy-
beans, and their oils.
Healthy Food Choices
In general, adults who eat vegetarian diets have lowered their
risks of mortality and several chronic diseases, including obesity,
high blood pressure, heart disease, and cancer. But there is noth-
ing mysterious or magical about the vegetarian diet; vegetarian-
ism is not a religion like Buddhism or Hinduism, but merely an
eating plan that selects plant foods to deliver needed nutrients.
The quality of the diet depends not on whether it includes meat,
but on whether the other food choices are nutritionally sound. A
diet that includes ample fruits, vegetables, whole grains,
legumes, nuts, and seeds is higher in fiber, antioxidant vitamins,
and phytochemicals, and lower in saturated fats than meat-based
diets. Variety is key to nutritional adequacy in a vegetarian diet.
Restrictive plans, such as macrobiotic diets, that limit selec-
tions to a few grains and vegetables cannot possibly deliver a full
array of nutrients.
If not properly balanced, any diet—vegetarian or otherwise—
can lack nutrients. Poorly planned vegetarian diets typically lack
iron, zinc, calcium, vitamin B12, and vitamin D; without planning,
the meat eater’s diet may lack vitamin A, vitamin C, folate, and
fiber, among others. Quite simply, the negative health aspects of
any diet, including vegetarian diets, reflect poor diet planning.
Careful attention to energy intake and specific problem nutrients
can ensure adequacy.
Keep in mind, too, that diet is only one factor influencing
health. Whatever a diet consists of, its context is also important:
no smoking, alcohol consumption in moderation (if at all), reg-
ular physical activity, adequate rest, and medical attention
when needed all contribute to a healthy life. Establishing these
healthy habits early in life seems to be the most important step
one can take to reduce the risks of later diseases (as Highlight 15
explains).
VEGETARIAN DIETS • 67
• Search for “vegetarian” at the Food and Drug
Administration’s site: www.fda.gov
• Visit the Vegetarian Resource Group: www.vrg.org
• Review another vegetarian diet pyramid developed by
Oldways Preservation Exchange Trust:
www.oldwayspt.org
* Calcium salts are often added during processing to coagulate the tofu.

68 • Highlight 2
1. S. I. Barr and G. E. Chapman, Perceptions and
practices of self-defined current vegetarian,
former vegetarian, and nonvegetarian
women, Journal of the American Dietetic Associ-
ation 102 (2002): 354–360.
2. J. Sabaté, The contribution of vegetarian diets
to human health, Forum of Nutrition 56
(2003): 218–220.
and Dietitians of Canada: Vegetarian diets,
(2003): 748–765; J. Sabaté, The contribution
of vegetarian diets to health and disease: A
paradigm shift? American Journal of Clinical
Nutrition 78 (2003): 502S–507S.
4. P. N. Singh, J. Sabaté, and G. E. Fraser, Does
low meat consumption increase life
expectancy in humans? American Journal of
Clinical Nutrition 78 (2003): 526S–532S.
5. P. K. Newby, K. L. Tucker, and A. Wolk, Risk of
overweight and obesity among semivegetar-
ian, lactovegetarian, and vegan women,
(2005): 1267–1274; N. Brathwaite and coau-
thors, Obesity, diabetes, hypertension, and
vegetarian status among Seventh-Day Adven-
tists in Barbados, Ethnicity and Disease 13
(2003): 34–39; E. H. Haddad and J. S. Tanz-
man, What do vegetarians in the United
States eat? American Journal of Clinical Nutri-
tion 78 (2003): 626S–632S.
6. S. E. Berkow and N. D. Barnard, Blood pres-
sure regulation and vegetarian diets, Nutrition
Reviews 63 (2005): 1–8; L. J. Appel, The effects
of protein intake on blood pressure and
cardiovascular disease, Current Opinion in
Lipidology 14 (2003): 55–59.
7. J. E. Cade and coauthors, The UK Women’s
Cohort Study: Comparison of vegetarians,
fish-eaters, and meat-eaters, Public Health
Nutrition 7 (2004): 871–878; E. H. Haddad and
J. S. Tanzman, What do vegetarians in the
United States eat? American Journal of Clinical
Nutrition 78 (2003): 626S–632S.
8. Third Report of the National Cholesterol Educa-
tion Program (NCEP) Expert Panel on Detection,
Evaluation, and Treatment of High Blood Choles-
terol in Adults (Adult Treatment Panel III), NIH
publication no. 02-5215 (Bethesda, Md.:
National Heart, Lung, and Blood Institute,
2002).
9. F. B. Hu, Plant-based foods and prevention
of cardiovascular disease: An overview,
(2003): 544S–551S.
10. F. M. Sacks and coauthors, Soy protein,
isoflavones, and cardiovascular health: An
American Heart Association Science Advisory
for professionals from the Nutrition Commit-
tee, Circulation 113 (2006): 1034–1044.
11. B. L. McVeigh and coauthors, Effect of soy
protein varying in isoflavone content on
serum lipids in healthy young men, Ameri-
can Journal of Clinical Nutrition 83 (2006):
244–251; D. Lukaczer and coauthors, Effect
of a low glycemic index diet with soy pro-
tein and phytosterols on CVD risk factors in
postmenopausal women, Nutrition 22
(2006): 104–113; M. S. Rosell and coauthors,
Soy intake and blood cholesterol concentra-
tions: A cross-sectional study of 1033 pre-
and postmenopausal women in the Oxford
arm of the European Prospective Investiga-
tion into Cancer and Nutrition, American
1391–1396; S. Tonstad, K. Smerud, and L.
Hoie, A comparison of the effects of 2 doses
of soy protein or casein on serum lipids,
serum lipoproteins, and plasma total homo-
cysteine in hypercholesterolemic subjects,
(2002): 78–84.
12. M. Kapiszewska, A vegetable to meat con-
sumption ratio as a relevant factor deter-
mining cancer preventive diet: The
Mediterranean versus other European coun-
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13. M. H. Lewin and coauthors, Red meat en-
hances the colonic formation of the DNA
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tions for colorectal cancer risk, Cancer Research
66 (2006): 1859–1865.
14. H. Chen and coauthors, Dietary patterns and
adenocarcinoma of the esophagus and distal
stomach, American Journal of Clinical Nutrition
75 (2002): 137–144.
15. C. Leitzmann, Vegetarian diets: What are the
advantages? Forum of Nutrition 57 (2005):
147–156.
16. M. Virginia, V. Melina, and A. R. Mangels, A
new food guide for North American vegetari-
ans, Journal of the American Dietetic Association
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R. Mangels, Considerations in planning vegan
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REFERENCES

Have you ever wondered what happens to the food you eat after you swallow
it? Or how your body extracts nutrients from food? Have you ever marveled
at how it all just seems to happen? Follow foods as they travel through the
digestive system. Learn how a healthy digestive system transforms whatever
food you give it—whether sirloin steak and potatoes or tofu and brussels
sprouts—into the nutrients that will nourish the cells of your body.
The CengageNOW logo
Figure 3.8: Animated! The Digestive Fate of a
Sandwich
Figure 3.11: Animated! The Vascular System
Foodcollection/Getty Images

This chapter takes you on the journey that transforms the foods you eat
into the nutrients featured in the later chapters. Then it follows the nutri-
ents as they travel through the intestinal cells and into the body to do their
work. This introduction presents a general overview of the processes com-
mon to all nutrients; later chapters discuss the specifics of digesting and
absorbing individual nutrients.
Digestion
Digestion is the body’s ingenious way of breaking down foods into nutrients in
preparation for absorption. In the process, it overcomes many challenges without
any conscious effort on your part. Consider these challenges:
1. Human beings breathe, eat, and drink through their mouths. Air taken in
through the mouth must go to the lungs; food and liquid must go to the stom-
ach. The throat must be arranged so that swallowing and breathing don’t inter-
fere with each other.
2. Below the lungs lies the diaphragm, a dome of muscle that separates the upper
half of the major body cavity from the lower half. Food must pass through this
wall to reach the stomach.
3. The materials within the digestive tract should be kept moving forward, slowly
but steadily, at a pace that permits all reactions to reach completion.
4. To move through the system, food must be lubricated with fluids. Too much
would form a liquid that would flow too rapidly; too little would form a paste
too dry and compact to move at all. The amount of fluids must be regulated to
keep the intestinal contents at the right consistency to move smoothly along.
5. When the digestive enzymes break food down, they need it in a finely divided
form, suspended in enough liquid so that every particle is accessible. Once di-
gestion is complete and the needed nutrients have been absorbed out of the
tract and into the body, the system must excrete the remaining residue. Excret-
ing all the water along with the solid residue, however, would be both wasteful
and messy. Some water must be withdrawn to leave a paste just solid enough to
be smooth and easy to pass.
6. The enzymes of the digestive tract are designed to digest carbohydrate, fat,
and protein. The walls of the tract, composed of living cells, are also made of
71
CHAPTER OUTLINE
Digestion • Anatomy of the Digestive
Tract • The Muscular Action of Digestion
• The Secretions of Digestion • The Final
Stage
Absorption • Anatomy of the
Absorptive System • A Closer Look at
the Intestinal Cells
The Circulatory Systems • The
Vascular System • The Lymphatic System
The Health and Regulation of the
GI Tract • Gastrointestinal
Bacteria • Gastrointestinal Hormones
and Nerve Pathways • The System at
Its Best
HIGHLIGHT 3 Common Digestive Problems
3
Digestion,
Absorption,
and Transport
C H A P T E R
digestion: the process by which food is
broken down into absorbable units.
• digestion = take apart
absorption: the uptake of nutrients by the
cells of the small intestine for transport into
either the blood or the lymph.
• absorb = suck in

72 • CHAPTER 3
carbohydrate, fat, and protein. These cells need protection against the action of
the powerful digestive juices that they secrete.
7. Once waste matter has reached the end of the tract, it must be excreted, but it
would be inconvenient and embarrassing if this function occurred continu-
ously. Provision must be made for periodic, voluntary evacuation.
The following sections show how the body elegantly and efficiently handles these
challenges.
Anatomy of the Digestive Tract
The gastrointestinal (GI) tract is a flexible muscular tube that extends from the
mouth, through the esophagus, stomach, small intestine, large intestine, and rectum
to the anus. Figure 3-1 traces the path followed by food from one end to the other. In
a sense, the human body surrounds the GI tract. The inner space within the GI tract,
called the lumen, is continuous from one end to the other. (GI anatomy terms ap-
pear in boldface type and are defined in the accompanying glossary.) Only when a
nutrient or other substance finally penetrates the GI tract’s wall does it enter the body
proper; many materials pass through the GI tract without being digested or absorbed.
Mouth The process of digestion begins in the mouth. As you chew, ◆ your teeth
crush large pieces of food into smaller ones, and fluids from foods, beverages, and
salivary glands blend with these pieces to ease swallowing. Fluids also help dissolve
the food so that you can taste it; only particles in solution can react with taste buds.
When stimulated, the taste buds detect one, or a combination, of the four basic taste
sensations: sweet, sour, bitter, and salty. Some scientists also include the flavor asso-
ciated with monosodium glutamate, sometimes called savory or its Asian name,
umami (oo-MOM-ee). In addition to these chemical triggers, aroma, texture, and
temperature also affect a food’s flavor. In fact, the sense of smell is thousands of
times more sensitive than the sense of taste.
The tongue allows you not only to taste food, but also to move food around the
mouth, facilitating chewing and swallowing. When you swallow a mouthful of
The process of digestion transforms all kinds of
foods into nutrients.
These terms are listed in order from
start to end of the digestive system.
lumen (LOO-men): the space
within a vessel, such as the
intestine.
mouth: the oral cavity containing
the tongue and teeth.
pharynx (FAIR-inks): the
passageway leading from the
nose and mouth to the larynx
and esophagus, respectively.
epiglottis (epp-ih-GLOTT-iss):
cartilage in the throat that
guards the entrance to the
trachea and prevents fluid or
food from entering it when a
person swallows.
• epi upon (over)
• glottis back of tongue
esophagus (ee-SOFF-ah-gus): the
food pipe; the conduit from the
mouth to the stomach.
sphincter (SFINK-ter): a circular
muscle surrounding, and able to
close, a body opening. Sphincters
are found at specific points along
the GI tract and regulate the flow
of food particles.
• sphincter band (binder)
esophageal (ee-SOF-ah-GEE-al)
sphincter: a sphincter muscle at
the upper or lower end of the
esophagus. The lower
esophageal sphincter is also
called the cardiac sphincter.
stomach: a muscular, elastic,
saclike portion of the digestive
tract that grinds and churns
swallowed food, mixing it with
acid and enzymes to form
chyme.
pyloric (pie-LORE-ic) sphincter:
the circular muscle that
separates the stomach from the
small intestine and regulates the
flow of partially digested food
into the small intestine; also
called pylorus or pyloric valve.
• pylorus gatekeeper
small intestine: a 10-foot length
of small-diameter intestine that
is the major site of digestion of
food and absorption of
nutrients. Its segments are the
duodenum, jejunum, and ileum.
gallbladder: the organ that stores
and concentrates bile. When it
receives the signal that fat is
present in the duodenum, the
gallbladder contracts and squirts
bile through the bile duct into
the duodenum.
pancreas: a gland that secretes
digestive enzymes and juices
into the duodenum. (The
pancreas also secretes hormones
into the blood that help to
maintain glucose homeostasis.)
duodenum (doo-oh-DEEN-um,
doo-ODD-num): the top portion
of the small intestine (about “12
fingers’ breadth” long in ancient
terminology).
• duodecim twelve
jejunum (je-JOON-um): the first
two-fifths of the small intestine
beyond the duodenum.
ileum (ILL-ee-um): the last
segment of the small intestine.
ileocecal (ill-ee-oh-SEEK-ul) valve:
the sphincter separating the
small and large intestines.
large intestine or colon
(COAL-un): the lower portion of
intestine that completes the
digestive process. Its segments
are the ascending colon, the
transverse colon, the descending
colon, and the sigmoid colon.
• sigmoid shaped like the
letter S (sigma in Greek)
appendix: a narrow blind sac
extending from the beginning of
the colon that stores lymph cells.
rectum: the muscular terminal part
of the intestine, extending from
the sigmoid colon to the anus.
anus (AY-nus): the terminal outlet
of the GI tract.
digestive system: all the organs
and glands associated with the
ingestion and digestion of food.
GLOSSARY OF GI ANATOMY TERMS
◆ The process of chewing is called
mastication (mass-tih-KAY-shun).
gastrointestinal (GI) tract: the digestive
tract. The principal organs are the stomach
and intestines.
• gastro = stomach
• intestinalis = intestine
©
Joe
Pelligrini/FoodPix/Jupiter
Images

DIGESTION, ABSORPTION, AND TRANSPORT • 73
FIGURE 3–1 The Gastrointestinal Tract
Ileocecal valve (sphincter)
Allows passage from small to
large intestine; prevents
backflow from large intestine
Appendix
Small intestine
Pancreas
Pancreatic duct
Large intestine (colon)
Rectum
Anus
Stores lymph cells
Secretes enzymes that digest
all energy-yielding nutrients to
smaller nutrient particles; cells
of wall absorb nutrients into
blood and lymph
Manufactures enzymes to
digest all energy-yielding
nutrients and releases
bicarbonate to neutralize acid
chyme that enters the small
intestine
Conducts pancreatic juice
from the pancreas to the
small intestine
Reabsorbs water and minerals;
passes waste (fiber, bacteria,
and unabsorbed nutrients)
along with water to the rectum
Stores waste prior to
elimination
Holds rectum closed;
opens to allow elimination
Stomach
Pancreas
Pancreatic duct
Small intestine
(duodenum,
jejunum, ileum)
Mouth
Salivary glands
Epiglottis
Bile duct
Conducts bile from the
gallbladder to the small
intestine
Gallbladder
Stores bile until needed
Liver
Manufactures bile salts,
detergent-like substances,
to help digest fats
Pyloric sphincter
Allows passage from stomach
to small intestine; prevents
backflow from small intestine
Stomach
Adds acid, enzymes, and
fluid; churns, mixes, and
grinds food to a liquid mass
Esophageal sphincters
Allow passage from mouth to
esophagus and from
esophagus to stomach;
prevent backflow from
stomach to esophagus and
from esophagus to mouth
Esophagus
Passes food from the mouth
to the stomach
Trachea
Allows air to pass to and
from lungs
Protects airway during
swallowing
Secrete saliva (contains
starch-digesting enzymes)
Chews and mixes food
with saliva
Pharynx
Directs food from mouth to
esophagus
Gallbladder
Pyloric
sphincter
Bile
duct
Ileocecal
valve
INGESTION
ELIMINATION
Mouth
Trachea
(to lungs)
Salivary
glands
Epiglottis
Esophagus
Lower
esophageal
sphincter
Liver
Appendix
Large intestine
(colon)
Rectum
Anus
Pharynx
Upper
esophageal
sphincter
food, it passes through the pharynx, a short tube that is shared by both the diges-
tive system and the respiratory system. To bypass the entrance to your lungs, the
epiglottis closes off your air passages so that you don’t choke when you swallow,
thus resolving the first challenge. (Choking is discussed on pp. 92–93.) After a
mouthful of food has been swallowed, it is called a bolus.
bolus (BOH-lus): a portion; with respect to
food, the amount swallowed at one time.
• bolos = lump

74 • CHAPTER 3
Esophagus to the Stomach The esophagus has a sphincter muscle at each
end. During a swallow, the upper esophageal sphincter opens. The bolus then
slides down the esophagus, which passes through a hole in the diaphragm (chal-
lenge 2) to the stomach. The lower esophageal sphincter at the entrance to the
stomach closes behind the bolus so that it proceeds forward and doesn’t slip back
into the esophagus (challenge 3). The stomach retains the bolus for a while in its up-
per portion. Little by little, the stomach transfers the food to its lower portion, adds
juices to it, and grinds it to a semiliquid mass called chyme. Then, bit by bit, the
stomach releases the chyme through the pyloric sphincter, which opens into the
small intestine and then closes behind the chyme.
Small Intestine At the beginning of the small intestine, the chyme bypasses the
opening from the common bile duct, which is dripping fluids (challenge 4) into the
small intestine from two organs outside the GI tract—the gallbladder and the
pancreas. The chyme travels on down the small intestine through its three seg-
ments—the duodenum, the jejunum, and the ileum—almost 10 feet of tubing
coiled within the abdomen.*
Large Intestine (Colon) Having traveled the length of the small intestine, the re-
maining contents arrive at another sphincter (challenge 3 again): the ileocecal
valve, at the beginning of the large intestine (colon) in the lower right side of
the abdomen. Upon entering the colon, the contents pass another opening. Any in-
testinal contents slipping into this opening would end up in the appendix, a blind
sac about the size of your little finger. The contents bypass this opening, however,
and travel along the large intestine up the right side of the abdomen, across the
front to the left side, down to the lower left side, and finally below the other folds of
the intestines to the back of the body, above the rectum.
As the intestinal contents pass to the rectum, the colon withdraws water, leaving
semisolid waste (challenge 5). The strong muscles of the rectum and anal canal
hold back this waste until it is time to defecate. Then the rectal muscles relax (chal-
lenge 7), and the two sphincters of the anus open to allow passage of the waste.
The Muscular Action of Digestion
In the mouth, chewing, the addition of saliva, and the action of the tonguetransform
food into a coarse mash that can be swallowed. After swallowing, you are generally
unaware of all the activity that follows. As is the case with so much else that happens
in the body, the muscles of the digestive tract meet internal needs without any con-
scious effort on your part. They keep things moving ◆ at just the right pace, slow
enough to get the job done and fast enough to make progress.
Peristalsis The entire GI tract is ringed with circular muscles. Surrounding these
rings of muscle are longitudinal muscles. When the rings tighten and the long
muscles relax, the tube is constricted. When the rings relax and the long muscles
tighten, the tube bulges. This action—called peristalsis—occurs continuously
and pushes the intestinal contents along (challenge 3 again). (If you have ever
watched a lump of food pass along the body of a snake, you have a good picture
of how these muscles work.)
The waves of contraction ripple along the GI tract at varying rates and intensi-
ties depending on the part of the GI tract and on whether food is present. For exam-
ple, waves occur three times per minute in the stomach, but they speed up to ten
times per minute when chyme reaches the small intestine. When you have just
eaten a meal, the waves are slow and continuous; when the GI tract is empty, the
intestine is quiet except for periodic bursts of powerful rhythmic waves. Peristalsis,
* The small intestine is almost 21/2 times shorter in living adults than it is at death, when muscles are
relaxed and elongated.
chyme (KIME): the semiliquid mass of partly
digested food expelled by the stomach into
the duodenum.
• chymos = juice
peristalsis (per-ih-STALL-sis): wavelike
muscular contractions of the GI tract that
push its contents along.
• peri = around
• stellein = wrap
◆ The ability of the GI tract muscles to move is
called their motility (moh-TIL-ih-tee).

along with sphincter muscles located at key places, keeps things moving
along.
Stomach Action The stomach has the thickest walls and strongest
muscles of all the GI tract organs. In addition to the circular and longi-
tudinal muscles, it has a third layer of diagonal muscles that also alter-
nately contract and relax (see Figure 3-2). These three sets of muscles
work to force the chyme downward, but the pyloric sphincter usually re-
mains tightly closed, preventing the chyme from passing into the duo-
denum of the small intestine. As a result, the chyme is churned and
forced down, hits the pyloric sphincter, and remains in the stomach.
Meanwhile, the stomach wall releases gastric juices. When the chyme is
completely liquefied, the pyloric sphincter opens briefly, about three
times a minute, to allow small portions of chyme to pass through. At
this point, the chyme no longer resembles food in the least.
Segmentation The circular muscles of the intestines rhythmically
contract and squeeze their contents (see Figure 3-3). These contractions,
FIGURE 3–3 Peristalsis and Segmentation
Chyme
Chyme
Longitudinal muscles
are outside.
The small intestine has two
muscle layers that work
together in peristalsis
and segmentation.
The inner circular muscles contract,
tightening the tube and pushing the
food forward in the intestine.
Circular muscles are
inside.
When the circular muscles relax, the
outer longitudinal muscles contract,
and the intestinal tube is loose.
As the circular and longitudinal
muscles tighten and relax, the chyme
moves ahead of the constriction.
Circular muscles contract, creating
segments within the intestine.
As each set of circular muscles
relaxes and contracts, the chyme is
broken up and mixed with digestive
juices.
These alternating contractions,
occurring 12 to 16 times per minute,
continue to mix the chyme and bring
the nutrients into contact with the
intestinal lining for absorption.
PERISTALSIS
SEGMENTATION
Diagonal
Circular
Longitudinal
FIGURE 3–2 Stomach Muscles
The stomach has three layers of muscles.

called segmentation, mix the
chyme and promote close contact
with the digestive juices and the ab-
sorbing cells of the intestinal walls
before letting the contents move
slowly along. Figure 3-3 illustrates
peristalsis and segmentation.
Sphincter Contractions Sphincter
muscles periodically open and close,
allowing the contents of the GI tract
to move along at a controlled pace
(challenge 3 again). At the top of the
esophagus, the upper esophageal
sphincter opens in response to swal-
lowing. At the bottom of the esopha-
gus, the lower esophageal sphincter
(sometimes called the cardiac sphinc-
ter because of its proximity to the
heart) prevents reflux of the stom-
ach contents. At the bottom of the
stomach, the pyloric sphincter, which
stays closed most of the time, holds
the chyme in the stomach long enough for it to be thoroughly mixed with gastric
juice and liquefied. The pyloric sphincter also prevents the intestinal contents from
backing up into the stomach. At the end of the small intestine, the ileocecal valve
performs a similar function, allowing the contents of the small intestine to empty
into the large intestine. Finally, the tightness of the rectal muscle is a kind of safety
device; together with the two sphincters of the anus, it prevents elimination until
you choose to perform it voluntarily (challenge 7). Figure 3-4 illustrates how
sphincter muscles contract and relax to close and open passageways.
The Secretions of Digestion
The breakdown of food into nutrients requires secretions from five different or-
gans: the salivary glands, the stomach, the pancreas, the liver (via the gallblad-
der), and the small intestine. These secretions enter the GI tract at various points
along the way, bringing an abundance of water (challenge 3 again) and a vari-
ety of enzymes.
Enzymes are formally introduced in Chapter 6, but for now a simple definition
will suffice. An enzyme is a protein that facilitates a chemical reaction—making
a molecule, breaking a molecule apart, changing the arrangement of a molecule,
or exchanging parts of molecules. As a catalyst, the enzyme itself remains un-
changed. The enzymes involved in digestion facilitate a chemical reaction known
as hydrolysis—the addition of water (hydro) to break (lysis) a molecule into
smaller pieces. The glossary (p. 77) identifies some of the common digestive en-
zymes and related terms; later chapters introduce specific enzymes. When learn-
ing about enzymes, it helps to know that the word ending -ase denotes an
enzyme. Enzymes are often identified by the organ they come from and the com-
pounds they work on. Gastric lipase, for example, is a stomach enzyme that acts
on lipids, whereas pancreatic lipase comes from the pancreas (and also works on
lipids).
Saliva The salivary glands, shown in Figure 3-5, squirt just enough saliva to
moisten each mouthful of food so that it can pass easily down the esophagus
(challenge 4). (Digestive glands and their secretions are defined in the glossary on
Esophagus
Stomach
Circular
muscle
Longitudinal muscle
Esophagus muscles relax,
opening the passageway.
Diaphragm muscles relax,
opening the passageway.
Esophagus muscles
contract, squeezing
on the inside.
Diaphragm muscles
contract, squeezing
on the outside.
FIGURE 3–4 An Example of a Sphincter Muscle
When the circular muscles of a sphincter contract, the passage closes; when they
relax, the passage opens.
segmentation (SEG-men-TAY-shun): a
periodic squeezing or partitioning of the
intestine at intervals along its length by its
circular muscles.
reflux: a backward flow.
• re = back
• flux = flow
catalyst (CAT-uh-list): a compound that
facilitates chemical reactions without itself
being changed in the process.
Salivary
glands
FIGURE 3–5 The Salivary Glands
The salivary glands secrete saliva into
the mouth and begin the digestive
process. Given the short time food is in
the mouth, salivary enzymes contribute
little to digestion.
76 • CHAPTER 3

p. 78.) The saliva contains water, salts, mucus, and enzymes that initiate the diges-
tion of carbohydrates. Saliva also protects the teeth and the linings of the mouth,
esophagus, and stomach from attack by substances that might harm them.
Gastric Juice In the stomach, gastric glands secrete gastric juice, a mix-
ture of water, enzymes, and hydrochloric acid, which acts primarily in pro-
tein digestion. The acid is so strong that it causes the sensation of heartburn if it
happens to reflux into the esophagus. Highlight 3, following this chapter, dis-
cusses heartburn, ulcers, and other common digestive problems.
The strong acidity of the stomach prevents bacterial growth and kills most
bacteria that enter the body with food. It would destroy the cells of the stomach
as well, but for their natural defenses. To protect themselves from gastric juice,
the cells of the stomach wall secrete mucus, a thick, slippery, white substance
that coats the cells, protecting them from the acid, enzymes, and disease-caus-
ing bacteria that might otherwise harm them (challenge 6).
Figure 3-6 shows how the strength of acids is measured—in pH ◆ units. Note
that the acidity of gastric juice registers below “2” on the pH scale—stronger
than vinegar. The stomach enzymes work most efficiently in the stomach’s
strong acid, but the salivary enzymes, which are swallowed with food, do not
work in acid this strong. Consequently, the salivary digestion of carbohydrate
gradually ceases when the stomach acid penetrates each newly swallowed bolus
of food. When they enter the stomach, salivary enzymes become just other pro-
teins to be digested.
Pancreatic Juice and Intestinal Enzymes By the time food leaves the stom-
ach, digestion of all three energy nutrients (carbohydrates, fats, and proteins)
has begun, and the action gains momentum in the small intestine. There the
pancreas contributes digestive juices by way of ducts leading into the duode-
num. The pancreatic juice contains enzymes that act on all three energy nu-
trients, and the cells of the intestinal wall also possess digestive enzymes on their
surfaces.
In addition to enzymes, the pancreatic juice contains sodium bicarbonate,
which is basic or alkaline—the opposite of the stomach’s acid (review Figure 3-
6). The pancreatic juice thus neutralizes the acidic chyme arriving in the small
intestine from the stomach. From this point on, the chyme remains at a neutral
or slightly alkaline pH. The enzymes of both the intestine and the pancreas work
best in this environment.
Bile Bile also flows into the duodenum. The liver continuously produces bile,
which is then concentrated and stored in the gallbladder. The gallbladder squirts
digestive enzymes: proteins found in
digestive juices that act on food
substances, causing them to break down
into simpler compounds.
-ase (ACE): a word ending denoting an
enzyme. The word beginning often
identifies the compounds the enzyme
works on. Examples include:
• carbohydrase (KAR-boe-HIGH-drase),
an enzyme that hydrolyzes
carbohydrates.
• lipase (LYE-pase), an enzyme that
hydrolyzes lipids (fats).
• protease (PRO-tee-ase), an enzyme
that hydrolyzes proteins.
hydrolysis (high-DROL-ih-sis): a chemical
reaction in which a major reactant is split
into two products, with the addition of a
hydrogen atom (H) to one and a hydroxyl
group (OH) to the other (from water,
H2O). (The noun is hydrolysis; the verb is
hydrolyze.)
• hydro water
• lysis breaking
GLOSSARY OF DIGESTIVE ENZYMES
pH of common substances:
Concentrated lye
Oven cleaner
14
12
Household ammonia
11
10
Baking soda
9
Pancreatic juice
Bile
8
Water
7
Urine
6
Coffee
5
Orange juice
4
Vinegar
3
Lemon juice
Gastric juice
2
1
Battery acid
0
Blood
Saliva
pH neutral
Basic
Acidic
13
FIGURE 3–6 The pH Scale
A substance’s acidity or alkalinity is
measured in pH units. The pH is the
negative logarithm of the hydrogen ion
concentration. Each increment represents
a tenfold increase in concentration of
hydrogen particles. This means, for
example, that a pH of 2 is 1000 times
stronger than a pH of 5.
◆ The lower the pH, the higher the H+ ion con-
centration and the stronger the acid. A pH
above 7 is alkaline, or base (a solution in
which OH ions predominate).
pH: the unit of measure expressing a
substance’s acidity or alkalinity.

78 • CHAPTER 3
the bile into the duodenum of the small intestine when fat arrives there. Bile is not
an enzyme; it is an emulsifier that brings fats into suspension in water so that
enzymes can break them down into their component parts. Thanks to all these se-
cretions, the three energy-yielding nutrients are digested in the small intestine (the
summary on p. 80 provides a table of digestive secretions and their actions).
The Final Stage
At this point, the three energy-yielding nutrients—carbohy-
drate, fat, and protein—have been disassembled and are
ready to be absorbed. Most of the other nutrients—vita-
mins, minerals, and water—need no such disassembly;
some vitamins and minerals are altered slightly during di-
gestion, but most are absorbed as they are. Undigested
residues, such as some fibers, are not absorbed. Instead, they
continue through the digestive tract, providing a semisolid
mass that helps exercise the muscles and keep them strong
enough to perform peristalsis efficiently. Fiber also retains
water, accounting for the pasty consistency of stools, and
thereby carries some bile acids, some minerals, and some
additives and contaminants with it out of the body.
By the time the contents of the GI tract reach the end
of the small intestine, little remains but water, a few dis-
solved salts and body secretions, and undigested materi-
als such as fiber. These enter the large intestine (colon).
In the colon, intestinal bacteria ferment some fibers,
producing water, gas, and small fragments of fat that
provide energy for the cells of the colon. The colon itself
retrieves all materials that the body can recycle—water
and dissolved salts (see Figure 3-7). The waste that is fi-
nally excreted has little or nothing of value left in it. The
body has extracted all that it can use from the food. Fig-
ure 3-8 summarizes digestion by following a sandwich
through the GI tract and into the body.
Transverse
colon
Ascending
colon
Opening from
small intestine
to large intestine
Appendix
Anus
Rectum
Sigmoid
colon
End of small
intestine
Descending
colon
FIGURE 3–7 The Colon
The colon begins with the ascending colon rising upward toward
the liver. It becomes the transverse colon as it turns and crosses the
body toward the spleen. The descending colon turns downward and
becomes the sigmoid colon, which extends to the rectum. Along the
way, the colon mixes the intestinal contents, absorbs water and
salts, and forms stools.
GLOSSARY OF DIGESTIVE GLANDS AND THEIR SECRETIONS
stools: waste matter discharged from the
colon; also called feces (FEE-seez).
These terms are listed in order from
start to end of the digestive tract.
glands: cells or groups of cells
that secrete materials for special
uses in the body. Glands may be
exocrine (EKS-oh-crin) glands,
secreting their materials “out”
(into the digestive tract or onto
the surface of the skin), or
endocrine (EN-doe-crin)
glands, secreting their materials
“in” (into the blood).
• exo outside
• endo inside
• krine to separate
salivary glands: exocrine glands
that secrete saliva into the mouth.
saliva: the secretion of the
salivary glands. Its principal
enzyme begins carbohydrate
digestion.
gastric glands: exocrine glands in
the stomach wall that secrete
gastric juice into the stomach.
• gastro stomach
gastric juice: the digestive
secretion of the gastric glands
of the stomach.
hydrochloric acid: an acid
composed of hydrogen and
chloride atoms (HCl) that is
normally produced by the
gastric glands.
mucus (MYOO-kus): a slippery
substance secreted by cells of
the GI lining (and other body
linings) that protects the cells
from exposure to digestive
juices (and other destructive
agents). The lining of the GI
tract with its coat of mucus is a
mucous membrane. (The noun
is mucus; the adjective is
mucous.)
liver: the organ that manufactures
bile. (The liver’s many other
functions are described in
Chapter 7.)
bile: an emulsifier that prepares
fats and oils for digestion; an
exocrine secretion made by the
liver, stored in the gallbladder,
and released into the small
intestine when needed.
emulsifier (ee-MUL-sih-fire): a
substance with both water-
soluble and fat-soluble portions
that promotes the mixing of oils
and fats in a watery solution.
pancreatic (pank-ree-AT-ic) juice:
the exocrine secretion of the
pancreas, containing enzymes for
the digestion of carbohydrate,
fat, and protein as well as
bicarbonate, a neutralizing agent.
The juice flows from the pancreas
into the small intestine through
the pancreatic duct. (The
pancreas also has an endocrine
function, the secretion of insulin
and other hormones.)
bicarbonate: an alkaline
compound with the formula
HCO3 that is secreted from the
pancreas as part of the pancreatic
juice. (Bicarbonate is also
produced in all cell fluids from
the dissociation of cabonic acid to
help maintain the body’s acid-
base balance.)

STOMACH: COLLECTING AND CHURNING, WITH SOME DIGESTION
Carbohydrate digestion continues until the mashed sandwich has been
mixed with the gastric juices; the stomach acid of the gastric juices
inactivates the salivary enzyme, and carbohydrate digestion ceases.
Proteins from the bread, seeds, and peanut butter begin to uncoil when
they mix with the gastric acid, making them available to the gastric
protease enzymes that begin to digest proteins.
Fat from the peanut butter forms a separate layer on top of the watery
mixture.
SMALL INTESTINE: DIGESTING AND ABSORBING
Sugars from the banana require so little digestion that they begin to
traverse the intestinal cells immediately on contact.
Starch digestion picks up when the pancreas sends pancreatic
enzymes to the small intestine via the pancreatic duct. Enzymes on the
surfaces of the small intestinal cells complete the process of breaking
down starch into small fragments that can be absorbed through the
intestinal cell walls and into the hepatic portal vein.
Fat from the peanut butter and seeds is emulsified with the watery
digestive fluids by bile. Now the pancreatic and intestinal lipases can
begin to break down the fat to smaller fragments that can be absorbed
through the cells of the small intestinal wall and into the lymph.
Protein digestion depends on the pancreatic and intestinal proteases.
Small fragments of protein are liberated and absorbed through the cells
of the small intestinal wall and into the hepatic portal vein.
Vitamins and minerals are absorbed.
Note: Sugars and starches are members of the carbohydrate family.
LARGE INTESTINE: REABSORBING AND ELIMINATING
Fluids and some minerals are absorbed.
Some fibers from the seeds, whole-wheat bread, peanut butter, and
banana are partly digested by the bacteria living there, and some of
these products are absorbed.
Most fibers pass through the large intestine and are excreted as feces;
some fat, cholesterol, and minerals bind to fiber and are also excreted.
MOUTH: CHEWING AND SWALLOWING, WITH LITTLE DIGESTION
Carbohydrate digestion begins as the salivary enzyme starts to break
down the starch from bread and peanut butter.
Fiber covering on the sesame seeds is crushed by the teeth, which
exposes the nutrients inside the seeds to the upcoming digestive
enzymes.
A B S O R P T I O N
E X C R E T I O N
Carbohydrate
Fiber
Protein
Fat
FIGURE 3–8 Animated! The Digestive Fate of a Sandwich
To review the digestive processes, follow a peanut butter and banana sandwich on whole-wheat, seasame seed bread through the GI
tract. As the graph on the right illustrates, digestion of the energy nutrients begins in different parts of the GI tract, but all are ready for
absorption by the time they reach the end of the small intestine.
To test your understanding
of these concepts, log on to

80 • CHAPTER 3
Absorption
Within three or four hours after you have eaten a dinner of beans and rice (or
spinach lasagna, or steak and potatoes) with vegetable, salad, beverage, and
dessert, your body must find a way to absorb the molecules derived from carbohy-
drate, protein, and fat digestion—and the vitamin and mineral molecules as well.
Most absorption takes place in the small intestine, one of the most elegantly de-
signed organ systems in the body. Within its 10-foot length, which provides a surface
area equivalent to a tennis court, the small intestine engulfs and absorbs the nutri-
ent molecules. To remove the molecules rapidly and provide room for more to be ab-
sorbed, a rush of circulating blood continuously washes the underside of this surface,
carrying the absorbed nutrients away to the liver and other parts of the body. Figure
3-9 describes how nutrients are absorbed by simple diffusion, facilitated diffusion, or
active transport. Later chapters provide details on specific nutrients. Before following
nutrients through the body, we must look more closely at the anatomy of the absorp-
tive system.
Anatomy of the Absorptive System
The inner surface of the small intestine looks smooth and slippery, but when viewed
through a microscope, it turns out to be wrinkled into hundreds of folds. Each fold is
contoured into thousands of fingerlike projections, as numerous as the hairs on vel-
vet fabric. These small intestinal projections are the villi. A single villus, magnified
still more, turns out to be composed of hundreds of cells, each covered with its own
microscopic hairs, the microvilli (see Figure 3-10 on p. 82). In the crevices between
the villi lie the crypts—tubular glands that secrete the intestinal juices into the
small intestine. Nearby goblet cells secrete mucus.
IN SUMMARY
As Figure 3-1 shows, food enters the mouth and travels down the esophagus
and through the upper and lower esophageal sphincters to the stomach, then
through the pyloric sphincter to the small intestine, on through the ileocecal
valve to the large intestine, past the appendix to the rectum, ending at the
anus. The wavelike contractions of peristalsis and the periodic squeezing of
segmentation keep things moving at a reasonable pace. Along the way, secre-
tions from the salivary glands, stomach, pancreas, liver (via the gallbladder),
and small intestine deliver fluids and digestive enzymes.
Summary of Digestive Secretions and Their Major Actions
Organ or Gland Target Organ Secretion Action
Salivary glands Mouth Saliva Fluid eases swallowing; salivary en-
zyme breaks down carbohydrate.a
Gastric glands Stomach Gastric juice Fluid mixes with bolus; hydrochloric
acid uncoils proteins; enzymes break
down proteins; mucus protects
stomach cells.a
Pancreas Small intestine Pancreatic juice Bicarbonate neutralizes acidic gastric
juices; pancreatic enzymes break down
carbohydrates, fats, and proteins.
Liver Gallbladder Bile Bile stored until needed.
Gallbladder Small intestine Bile Bile emulsifies fat so enzymes can
attack.
Intestinal glands Small intestine Intestinal juice Intestinal enzymes break down carbo-
hydrate, fat, and protein fragments;
mucus protects the intestinal wall.
Food must first be digested and absorbed
before the body can use it.
villi (VILL-ee, VILL-eye): fingerlike projections
from the folds of the small intestine; singular
villus.
microvilli (MY-cro-VILL-ee, MY-cro-VILL-eye):
tiny, hairlike projections on each cell of every
villus that can trap nutrient particles and
transport them into the cells; singular
microvillus.
crypts (KRIPTS): tubular glands that lie
between the intestinal villi and secrete
intestinal juices into the small intestine.
goblet cells: cells of the GI tract (and lungs)
that secrete mucus.
Foodcollection/Getty
Images
a Saliva and gastric juices also contain lipases, but most fat breakdown occurs in the small intestines.

The villi are in constant motion. Each villus is lined by a thin sheet of muscle, so
it can wave, squirm, and wriggle like the tentacles of a sea anemone. Any nutrient
molecule small enough to be absorbed is trapped among the microvilli that coat
the cells and then drawn into the cells. Some partially digested nutrients are caught
in the microvilli, digested further by enzymes there, and then absorbed into the
cells.
A Closer Look at the Intestinal Cells
The cells of the villi are among the most amazing in the body, for they recognize and
select the nutrients the body needs and regulate their absorption. As already de-
scribed, each cell of a villus is coated with thousands of microvilli, which project
from the cell’s membrane (review Figure 3-10). In these microvilli, and in the mem-
brane, lie hundreds of different kinds of enzymes and “pumps,” which recognize
and act on different nutrients. Descriptions of specific enzymes and “pumps” for
each nutrient are presented in the following chapters where appropriate; the point
here is that the cells are equipped to handle all kinds and combinations of foods and
nutrients.
Specialization in the GI Tract A further refinement of the system is that the cells
of successive portions of the intestinal tract are specialized to absorb different nutri-
ents. The nutrients that are ready for absorption early are absorbed near the top of
the tract; those that take longer to be digested are absorbed farther down. Registered
dietitians and medical professionals who treat digestive disorders learn the special-
ized absorptive functions of different parts of the GI tract so that if one part becomes
dysfunctional, the diet can be adjusted accordingly.
The Myth of “Food Combining” The idea that people should not eat certain
food combinations (for example, fruit and meat) at the same meal, because the di-
gestive system cannot handle more than one task at a time, is a myth. The art of
“food combining” (which actually emphasizes “food separating”) is based on this
idea, and it represents faulty logic and a gross underestimation of the body’s capa-
bilities. In fact, the contrary is often true; foods eaten together can enhance each
Outside
cell
Inside
cell
Carrier loads
nutrient on
outside of cell . . .
. . . and then
releases it on
inside of cell.
Carrier loads
nutrient on
outside of cell . . .
. . . and then
releases it on
inside of cell.
SIMPLE
DIFFUSION
FACILITATED
DIFFUSION
ACTIVE
TRANSPORT
Energy
Cell
membrane
Some nutrients (such as glucose and
amino acids) must be absorbed
actively. These nutrients move against
a concentration gradient, which
requires energy.
Some nutrients (such as water
and small lipids) are absorbed
by simple diffusion. They cross
into intestinal cells freely.
Some nutrients (such as the water-soluble
vitamins) are absorbed by facilitated diffusion.
They need a specific carrier to transport them
from one side of the cell membrane to the
other. (Alternatively, facilitated diffusion may
occur when the carrier changes the cell
membrane in such a way that the nutrients can
pass through.)
FIGURE 3–9 Absorption of Nutrients
Absorption of nutrients into intestinal cells typically occurs by simple diffusion, facilitated diffusion, or active transport.

82 • CHAPTER 3
Small intestine
Stomach
Folds with villi
on them
A villus
Capillaries
Lymphatic vessel
(lacteal)
The wall of the small intestine is
wrinkled into thousands of
folds and is carpeted with villi.
Circular
muscles
Longitudinal
muscles
Crypts
If you have ever watched a sea
anemone with its fingerlike
projections in constant motion,
you have a good picture of how
the intestinal villi move.
This is a photograph of part of
an actual human intestinal cell
with microvilli.
Each villus in turn is covered
with even smaller projections,
the microvilli. Microvilli on the
cells of villi provide the
absorptive surfaces that allow
the nutrients to pass through
to the body.
Microvilli
Lymphatic
vessel
Vein
Artery
Goblet cells
©
Don
W.
Fawcett
©
Bill
Crew/Super
Stock
FIGURE 3–10 The Small Intestinal Villi
Absorption of nutrients into intestinal cells typically occurs by simple diffusion or active transport.
other’s use by the body. For example, vitamin C in a pineapple or other citrus fruit
can enhance the absorption of iron from a meal of chicken and rice or other iron-
containing foods. Many other instances of mutually beneficial interactions are pre-
sented in later chapters.
Preparing Nutrients for Transport When a nutrient molecule has crossed the
cell of a villus, it enters either the bloodstream or the lymphatic system. Both trans-
port systems supply vessels to each villus, as shown in Figure 3-10. The water-soluble

nutrients and the smaller products of fat digestion are released directly into the
bloodstream and guided directly to the liver where their fate and destination will be
determined.
The larger fats and the fat-soluble vitamins are insoluble in water, however, and
blood is mostly water. The intestinal cells assemble many of the products of fat di-
gestion into larger molecules. These larger molecules cluster together with special
proteins, forming chylomicrons. ◆ Because these chylomicrons cannot pass into
the capillaries, they are released into the lymphatic system instead; the chylomi-
crons move through the lymph and later enter the bloodstream at a point near the
heart, thus bypassing the liver at first. Details follow.
◆ Chylomicrons (kye-lo-MY-cronz) are
described in Chapter 5.
The many folds and villi of the small intestine dramatically increase its sur-
face area, facilitating nutrient absorption. Nutrients pass through the cells of
the villi and enter either the blood (if they are water soluble or small fat frag-
ments) or the lymph (if they are fat soluble).
IN SUMMARY
The Circulatory Systems
Once a nutrient has entered the bloodstream, it may be transported to any of the
cells in the body, from the tips of the toes to the roots of the hair. The circulatory sys-
tems deliver nutrients wherever they are needed.
The Vascular System
The vascular, or blood circulatory, system is a closed system of vessels through which
blood flows continuously, with the heart serving as the pump (see Figure 3-11, p. 84).
As the blood circulates through this system, it picks up and delivers materials as
needed.
All the body tissues derive oxygen and nutrients from the blood and deposit car-
bon dioxide and other wastes back into the blood. The lungs exchange carbon
dioxide (which leaves the blood to be exhaled) and oxygen (which enters the blood
to be delivered to all cells). The digestive system supplies the nutrients to be picked
up. In the kidneys, wastes other than carbon dioxide are filtered out of the blood to
be excreted in the urine.
Blood leaving the right side of the heart circulates through the lungs and then back
to the left side of the heart. The left side of the heart then pumps the blood out of the
aorta through arteries to all systems of the body. The blood circulates in the capil-
laries, where it exchanges material with the cells and then collects into veins, which
return it again to the right side of the heart. In short, blood travels this simple route:
• Heart to arteries to capillaries to veins to heart
The routing of the blood leaving the digestive system has a special feature. The
blood is carried to the digestive system (as to all organs) by way of an artery, which
(as in all organs) branches into capillaries to reach every cell. Blood leaving the di-
gestive system, however, goes by way of a vein. The hepatic portal vein directs
blood not back to the heart, but to another organ—the liver. This vein again
branches into capillaries so that every cell of the liver has access to the blood. Blood
leaving the liver then again collects into a vein, called the hepatic vein, which re-
turns blood to the heart.
The route is:
• Heart to arteries to capillaries (in intestines) to hepatic portal vein to capil-
laries (in liver) to hepatic vein to heart
aorta (ay-OR-tuh): the large, primary artery
that conducts blood from the heart to the
body’s smaller arteries.
arteries: vessels that carry blood from the
heart to the tissues.
capillaries (CAP-ill-aries): small vessels that
branch from an artery. Capillaries connect
arteries to veins. Exchange of oxygen,
nutrients, and waste materials takes place
across capillary walls.
veins (VANES): vessels that carry blood to the
heart.
hepatic portal vein: the vein that collects
blood from the GI tract and conducts it to
capillaries in the liver.
• portal = gateway
hepatic vein: the vein that collects blood
from the liver capillaries and returns it to the
heart.
• hepatic = liver

84 • CHAPTER 3
Figure 3-12 shows the liver’s key position in nutrient transport. An anatomist
studying this system knows there must be a reason for this special arrangement.
The liver’s placement ensures that it will be first to receive the nutrients absorbed
from the GI tract. In fact, the liver has many jobs to do in preparing the absorbed
nutrients for use by the body. It is the body’s major metabolic organ.
You might guess that, in addition, the liver serves as a gatekeeper to defend
against substances that might harm the heart or brain. This is why, when people
ingest poisons that succeed in passing the first barrier (the intestinal cells), the liver
quite often suffers the damage—from viruses such as hepatitis, from drugs such as
barbiturates or alcohol, from toxins such as pesticide residues, and from contami-
nants such as mercury. Perhaps, in fact, you have been undervaluing your liver,
not knowing what heroic tasks it quietly performs for you.
The Lymphatic System
The lymphatic system provides a one-way route for fluid from the tissue
spaces to enter the blood. Unlike the vascular system, the lymphatic system has
Pulmonary vein
Blood loses carbon dioxide and
picks up oxygen in the lungs and
returns to the left side of the heart
by way of the pulmonary vein.
r
Blood leaves the left side of the
heart by way of the aorta, the
main artery that launches blood
on its course through the body.
Blood may leave the aorta to go
to the upper body and head;
or
Blood may leave the aorta to go
to the lower body.
Blood may go to the digestive
tract and then the liver;
or
Blood may go to the pelvis,
kidneys, and legs.
Blood leaves the right side of the
heart by way of the pulmonary
artery.
Hepatic
vein
Pulmonary artery
Lymph from most of the body’s
organs, including the digestive
system, enters the bloodstream
near the heart.
Blood returns to the right side
of the heart.
Arteries
Capillaries
Veins
Lymph vessels
Head and
upper body
Lungs
Aorta
Left
side
Right
side
Liver
Hepatic
artery
Digestive
tract
Hepatic portal
vein
Lymph
Entire body
Heart
1
5
4
3
2
5
4
2
3
7
7
6
6
1
Key:
FIGURE 3–11 Animated! The Vascular System
To test your understanding
of these concepts, log on to
lymphatic (lim-FAT-ic) system: a loosely
organized system of vessels and ducts that
convey fluids toward the heart. The GI part
of the lymphatic system carries the products
of fat digestion into the bloodstream.

no pump; instead, lymph circulates between the cells of the body and collects
into tiny vessels. The fluid moves from one portion of the body to another as
muscles contract and create pressure here and there. Ultimately, much of the
lymph collects in the thoracic duct behind the heart. The thoracic duct opens
into the subclavian vein, where the lymph enters the bloodstream. Thus nu-
trients from the GI tract that enter lymphatic vessels ◆ (large fats and fat-solu-
ble vitamins) ultimately enter the bloodstream, circulating through arteries,
capillaries, and veins like the other nutrients, with a notable exception—they
bypass the liver at first.
Once inside the vascular system, the nutrients can travel freely to any destina-
tion and can be taken into cells and used as needed. What becomes of them is de-
scribed in later chapters.
Vessels gather up nutrients and
reabsorbed water and salts from all
over the digestive tract.
Not shown here:
Parallel to these vessels (veins) are
other vessels (arteries) that carry
oxygen-rich blood from the heart
to the intestines.
The vessels merge into the hepatic
portal vein, which conducts all
absorbed materials to the liver.
Capillaries
Hepatic vein
Hepatic
artery
Hepatic portal vein
Vessels
The hepatic artery brings a supply of
freshly oxygenated blood (not loaded
with nutrients) from the lungs to supply
oxygen to the liver’s own cells.
Capillaries branch all over the liver,
making nutrients and oxygen available
to all its cells and giving the cells access
to blood from the digestive system.
The hepatic vein gathers up blood in
the liver and returns it to the heart.
In contrast, nutrients absorbed into lymph
do not go to the liver first. They go to the
heart, which pumps them to all the body’s
cells. The cells remove the nutrients they
need, and the liver then has to deal only
with the remnants.
1
2
3
4
5
4
5
3
2
1
FIGURE 3–12 The Liver
◆ The lymphatic vessels of the intestine that
take up nutrients and pass them to the
lymph circulation are called lacteals
(LACK-tee-als).
Nutrients leaving the digestive system via the blood are routed directly to the
liver before being transported to the body’s cells. Those leaving via the lym-
phatic system eventually enter the vascular system but bypass the liver at first.
IN SUMMARY
lymph (LIMF): a clear yellowish fluid that is
similar to blood except that it contains no
red blood cells or platelets. Lymph from
the GI tract transports fat and fat-soluble
vitamins to the bloodstream via lymphatic
vessels.
thoracic (thor-ASS-ic) duct: the main
lymphatic vessel that collects lymph and
drains into the left subclavian vein.
subclavian (sub-KLAY-vee-an) vein: the
vein that provides passageway from the
lymphatic system to the vascular system.

86 • CHAPTER 3
The Health and Regulation
of the GI Tract
This section describes the bacterial conditions and hormonal regulation of a healthy
GI tract, but many factors ◆ can influence normal GI function. For example, peri-
stalsis and sphincter action are poorly coordinated in newborns, so infants tend to
“spit up” during the first several months of life. Older adults often experience consti-
pation, in part because the intestinal wall loses strength and elasticity with age,
which slows GI motility. Diseases can also interfere with digestion and absorption
and often lead to malnutrition. Lack of nourishment, in general, and lack of certain
dietary constituents such as fiber, in particular, alter the structure and function of GI
cells. Quite simply, GI tract health depends on adequate nutrition.
Gastrointestinal Bacteria
An estimated 10 trillion bacteria ◆ representing some 400 or more different species
and subspecies live in a healthy GI tract. The prevalence of different bacteria in var-
ious parts of the GI tract depends on such factors as pH, peristalsis, diet, and other
microorganisms. Relatively few microorganisms can live in the low pH of the stom-
ach with its relatively rapid peristalsis, whereas the neutral pH and slow peristalsis
of the lower small intestine and the large intestine permit the growth of a diverse
and abundant bacterial population.1
Most of these bacteria normally do the body no harm and may actually do some
good. Provided that the normal intestinal flora are thriving, infectious bacteria
have a hard time establishing themselves to launch an attack on the system.
Diet is one of several factors that influence the body’s bacterial population and
environment. Consider yogurt, for example.2 Yogurt contains Lactobacillus and
other living bacteria. These microorganisms are considered probiotics because
they change the conditions and native bacterial colonies in the GI tract in ways
that seem to benefit health.3 The potential GI health benefits of probiotics include
helping to alleviate diarrhea, constipation, inflammatory bowel disease, ulcers, al-
lergies, and lactose intolerance; enhance immune function; and protect against
colon cancer.4 Some probiotics may have adverse effects under certain circum-
stances.5 Research studies continue to explore how diet influences GI bacteria and
which foods—with their probiotics—affect GI health.
GI bacteria also digest fibers and complex proteins.6 ◆ In doing so, the bacteria
produce nutrients such as short fragments of fat that the cells of the colon use for
energy. Bacteria in the GI tract also produce several vitamins, ◆ including a signif-
icant amount of vitamin K, although the amount is insufficient to meet the body’s
total need for that vitamin.
Gastrointestinal Hormones and Nerve
Pathways
The ability of the digestive tract to handle its ever-changing contents routinely il-
lustrates an important physiological principle that governs the way all living
things function—the principle of homeostasis. Simply stated, survival depends
on body conditions staying about the same; if they deviate too far from the norm,
the body must “do something” to bring them back to normal. The body’s regula-
tion of digestion is one example of homeostatic regulation. The body also regu-
lates its temperature, its blood pressure, and all other aspects of its blood
chemistry in similar ways.
Two intricate and sensitive systems coordinate all the digestive and absorptive
processes: the hormonal (or endocrine) system and the nervous system. Even be-
fore the first bite of food is taken, the mere thought, sight, or smell of food can trig-
◆ Factors influencing GI function:
• Physical immaturity
• Aging
• Illness
• Nutrition
◆ Bacteria in the intestines are sometimes re-
ferred to as flora or microflora.
◆ Food components (such as fibers) that are
not digested in the small intestine, but are
used instead as food by bacteria to encour-
age their growth are called prebiotics.
◆ Vitamins produced by bacteria include:
• Biotin
• Folate
• Vitamin B6
• Vitamin B12
• Vitamin K
yogurt: milk product that results from
the fermentation of lactic acid in milk by
Lactobacillus bulgaricus and Streptococcus
thermophilus.
probiotics: living microorganisms found in
foods that, when consumed in sufficient
quantities, are beneficial to health.
• pro = for
• bios = life
homeostasis (HOME-ee-oh-STAY-sis): the
maintenance of constant internal conditions
(such as blood chemistry, temperature,
and blood pressure) by the body’s control
systems. A homeostatic system is constantly
reacting to external forces to maintain limits
set by the body’s needs.
• homeo = the same
• stasis = staying

ger a response from these systems. Then, as food travels through the GI tract, it ei-
ther stimulates or inhibits digestive secretions by way of messages that are carried
from one section of the GI tract to another by both hormones ◆ and nerve path-
ways. (Appendix A presents a brief summary of the body’s hormonal system and
nervous system.)
Notice that the kinds of regulation described next are all examples of feedback
mechanisms. A certain condition demands a response. The response changes that
condition, and the change then cuts off the response. Thus the system is self-correct-
ing. Examples follow:
• The stomach normally maintains a pH between 1.5 and 1.7. How does it stay that
way? Food entering the stomach stimulates cells in the stomach wall to re-
lease the hormone gastrin. Gastrin, in turn, stimulates the stomach glands
to secrete the components of hydrochloric acid. When pH 1.5 is reached, the
acid itself turns off the gastrin-producing cells. They stop releasing gastrin,
and the glands stop producing hydrochloric acid. Thus the system adjusts
itself.
Nerve receptors in the stomach wall also respond to the presence of food
and stimulate the gastric glands to secrete juices and the muscles to contract.
As the stomach empties, the receptors are no longer stimulated, the flow of
juices slows, and the stomach quiets down.
• The pyloric sphincter opens to let out a little chyme, then closes again. How does it
know when to open and close? When the pyloric sphincter relaxes, acidic
chyme slips through. The cells of the pyloric muscle on the intestinal side
sense the acid, causing the pyloric sphincter to close tightly. Only after the
chyme has been neutralized by pancreatic bicarbonate and the juices sur-
rounding the pyloric sphincter have become alkaline can the muscle relax
again. This process ensures that the chyme will be released slowly enough to
be neutralized as it flows through the small intestine. This is important be-
cause the small intestine has less of a mucous coating than the stomach does
and so is not as well protected from acid.
• As the chyme enters the intestine, the pancreas adds bicarbonate to it so that the
intestinal contents always remain at a slightly alkaline pH. How does the pancreas
know how much to add? The presence of chyme stimulates the cells of the
duodenum wall to release the hormone secretin into the blood. When se-
cretin reaches the pancreas, it stimulates the pancreas to release its bicarbon-
ate-rich juices. Thus, whenever the duodenum signals that acidic chyme is
present, the pancreas responds by sending bicarbonate to neutralize it.
When the need has been met, the cells of the duodenum wall are no longer
stimulated to release secretin, the hormone no longer flows through the
blood, the pancreas no longer receives the message, and it stops sending
pancreatic juice. Nerves also regulate pancreatic secretions.
• Pancreatic secretions contain a mixture of enzymes to digest carbohydrate, fat, and
protein. How does the pancreas know how much of each type of enzyme to provide?
This is one of the most interesting questions physiologists have asked.
Clearly, the pancreas does know what its owner has been eating, and it se-
cretes enzyme mixtures tailored to handle the food mixtures that have been
arriving recently (over the last several days). Enzyme activity changes pro-
portionately in response to the amounts of carbohydrate, fat, and protein in
the diet. If a person has been eating mostly carbohydrates, the pancreas
makes and secretes mostly carbohydrases; if the person’s diet has been high
in fat, the pancreas produces more lipases; and so forth. Presumably, hor-
mones from the GI tract, secreted in response to meals, keep the pancreas in-
formed as to its digestive tasks. The day or two lag between the time a
person’s diet changes dramatically and the time digestion of the new diet be-
comes efficient explains why dietary changes can “upset digestion” and
should be made gradually.
◆ In general, any gastrointestinal hormone
may be called an enterogastrone (EN-ter-
oh-GAS-trone), but the term refers specifically
to any hormone that slows motility and
inhibits gastric secretions.
hormones: chemical messengers. Hormones
are secreted by a variety of glands in
response to altered conditions in the body.
Each hormone travels to one or more
specific target tissues or organs, where
it elicits a specific response to maintain
homeostasis.
gastrin: a hormone secreted by cells in the
stomach wall. Target organ: the glands of
the stomach. Response: secretion of gastric
acid.
secretin (see-CREET-in): a hormone produced
by cells in the duodenum wall. Target organ:
the pancreas. Response: secretion of
bicarbonate-rich pancreatic juice.

88 • CHAPTER 3
• Why don’t the digestive enzymes damage the pancreas? The pancreas protects it-
self from harm by producing an inactive form of the enzymes. ◆ It releases
these proteins into the small intestine where they are activated to become
enzymes. In pancreatitis, the digestive enzymes become active within the in-
fected pancreas, causing inflammation and damaging the delicate pancreatic
tissues.
• When fat is present in the intestine, the gallbladder contracts to squirt bile into the
intestine to emulsify the fat. How does the gallbladder get the message that fat is
present? Fat in the intestine stimulates cells of the intestinal wall to release
the hormone cholecystokinin (CCK). This hormone, traveling by way of
the blood to the gallbladder, stimulates it to contract, releasing bile into the
small intestine. Cholecystokinin also travels to the pancreas, stimulates it to
secrete its juices, releasing bicarbonate and enzymes into the small intestine.
Once the fat in the intestine is emulsified and enzymes have begun to work
on it, the fat no longer provokes release of the hormone, and the message to
contract is canceled. (By the way, fat emulsification can continue even after
a diseased gallbladder has been surgically removed because the liver can de-
liver bile directly to the small intestine.)
• Fat and protein take longer to digest than carbohydrate does. When fat or protein is
present, intestinal motility slows to allow time for its digestion. How does the intes-
tine know when to slow down? Cholecystokinin is released in response to fat or
protein in the small intestine. In addition to its role in fat emulsification and
digestion, cholecystokinin slows GI tract motility. Slowing the digestive
process helps to maintain a pace that allows all reactions to reach completion.
Hormonal and nervous mechanisms like these account for much of the body’s
ability to adapt to changing conditions.
Table 3-1 summarizes the actions of these GI hormones.
Once a person has started to learn the answers to questions like these, it may be
hard to stop. Some people devote their whole lives to the study of physiology. For now,
however, these few examples illustrate how all the processes throughout the digestive
system are precisely and automatically regulated without any conscious effort.
◆ The inactive precursor of an enzyme is
called a proenzyme or zymogen
(ZYE-mo-jen).
• pro = before
• zym = concerning enzymes
• gen = to produce
TABLE 3-1 The Primary Actions of GI Hormones
Hormone: Responds to: Secreted from: Stimulates: Response:
Gastrin Food in the stomach Stomach wall Stomach glands Hydrochloric acid secreted into the stomach
Secretin Acidic chyme in the small intestine Duodenal wall Pancreas Bicarbonate-rich juices secreted into the small
intestine
Cholecystokinin Fat or protein in the small intestine Intestinal wall Gallbladder Bile secreted into the duodenum
Pancreas Bicarbonate- and enzyme-rich juices secreted into
the small intestine
A diverse and abundant bacteria population support GI health. The regula-
tion of GI processes depends on the coordinated efforts of the hormonal system
and the nervous system; together, digestion and absorption transform foods
into nutrients.
IN SUMMARY
The System at Its Best
This chapter describes the anatomy of the digestive tract on several levels: the se-
quence of digestive organs, the cells and structures of the villi, and the selective ma-
cholecystokinin (COAL-ee-SIS-toe-KINE-in),
or CCK: a hormone produced by cells of the
intestinal wall. Target organ: the gallbladder.
Response: release of bile and slowing of GI
motility.

chinery of the cell membranes. The intricate architec-
ture of the digestive system makes it sensitive and re-
sponsive to conditions in its environment. Several
different kinds of GI tract cells confer specific immunity
against intestinal diseases such as inflammatory bowel
disease. In addition, secretions from the GI tract—
saliva, mucus, gastric acid, and digestive enzymes—not
only help with digestion, but also defend against for-
eign invaders. Together the GI’s team of bacteria, cells,
and secretions defend the body against numerous chal-
lenges.7 Knowing the optimal conditions will help you
to make choices that promote the best functioning of
the system.
One indispensable condition is good health of the
digestive tract itself. This health is affected by such
lifestyle factors as sleep, physical activity, and state of
mind. Adequate sleep allows for repair and mainte-
nance of tissue and removal of wastes that might im-
pair efficient functioning. Activity promotes healthy
muscle tone. Mental state influences the activity of regulatory nerves and hor-
mones; for healthy digestion, you should be relaxed and tranquil at mealtimes.
Another factor in GI health is the kind of meals you eat. Among the character-
istics of meals that promote optimal absorption of nutrients are those mentioned
in Chapter 2: balance, moderation, variety, and adequacy. Balance and modera-
tion require having neither too much nor too little of anything. For example, too
much fat can be harmful, but some fat is beneficial in slowing down intestinal
motility and providing time for absorption of some of the nutrients that are slow
to be absorbed.
Variety is important for many reasons, but one is that some food constituents in-
terfere with nutrient absorption. For example, some compounds common in high-
fiber foods such as whole-grain cereals, certain leafy green vegetables, and legumes
bind with minerals. To some extent, then, the minerals in those foods may become
unavailable for absorption. These high-fiber foods are still valuable, but they need
to be balanced with a variety of other foods that can provide the minerals.
As for adequacy—in a sense, this entire book is about dietary adequacy. But
here, at the end of this chapter, is a good place to underline the interdependence of
the nutrients. It could almost be said that every nutrient depends on every other.
All the nutrients work together, and all are present in the cells of a healthy diges-
tive tract. To maintain health and promote the functions of the GI tract, you should
make balance, moderation, variety, and adequacy features of every day’s menus.
Nourishing foods and pleasant conversations
support a healthy digestive system.
A healthy digestive system can adjust to almost any diet and can handle any combina-
tion of foods with ease.
■ Describe the physical and emotional environment that typically surrounds your
meals, including how it affects you and how it might be improved.
■ Detail any GI discomforts you may experience regularly and include suggestions
to alleviate or prevent their occurrence (see Highlight 3).
■ List any changes you can make in your eating habits to promote overall GI
health.
AJA
Productions/Getty
Images

90 • CHAPTER 3
• Visit the Center for Digestive Health and Nutrition:
www.gihealth.com
• Visit the patient information section of the American
College of Gastroenterology: www.acg.gi.org
1. Describe the challenges associated with digesting food and
the solutions offered by the human body. (pp. 71–80)
2. Describe the path food follows as it travels through the
digestive system. Summarize the muscular actions that
take place along the way. (pp. 72–76)
3. Name five organs that secrete digestive juices. How do
the juices and enzymes facilitate digestion? (pp. 76–78)
4. Describe the problems associated with absorbing nutri-
ents and the solutions offered by the small intestine.
(pp. 80–83)
5. How is blood routed through the digestive system?
Which nutrients enter the bloodstream directly? Which
are first absorbed into the lymph? (pp. 83–85)
6. Describe how the body coordinates and regulates the
processes of digestion and absorption. (pp. 86–88)
7. How does the composition of the diet influence the
functioning of the GI tract? (p. 89)
8. What steps can you take to help your GI tract function
at its best? (p. 89)
1. The semiliquid, partially digested food that travels
through the intestinal tract is called:
a. bile.
b. lymph.
c. chyme.
d. secretin.
2. The muscular contractions that move food through the
GI tract are called:
a. hydrolysis.
b. sphincters.
c. peristalsis.
d. bowel movements.
3. The main function of bile is to:
a. emulsify fats.
b. catalyze hydrolysis.
c. slow protein digestion.
d. neutralize stomach acidity.
4. The pancreas neutralizes stomach acid in the small intes-
tine by secreting:
a. bile.
b. mucus.
c. enzymes.
d. bicarbonate.
5. Which nutrient passes through the GI tract mostly undi-
gested and unabsorbed?
a. fat
b. fiber
c. protein
d. carbohydrate
6. Absorption occurs primarily in the:
a. mouth.
b. stomach.
c. small intestine.
d. large intestine.
7. All blood leaving the GI tract travels first to the:
a. heart.
b. liver.
c. kidneys.
d. pancreas.
8. Which nutrients leave the GI tract by way of the
lymphatic system?
a. water and minerals
b. proteins and minerals
c. all vitamins and minerals
d. fats and fat-soluble vitamins
9. Digestion and absorption are coordinated by the:
a. pancreas and kidneys.
b. liver and gallbladder.
c. hormonal system and the nervous system.
d. vascular system and the lymphatic system.
10. Gastrin, secretin, and cholecystokinin are examples of:
a. crypts.
b. enzymes.
c. hormones.
d. goblet cells.
STUDY QUESTIONS

1. P. B. Eckburg and coauthors, Diversity of the
human intestinal microbial flora, Science
308 (2005): 1635–1638; W. L. Hao and Y. K.
Lee, Microflora of the gastrointestinal tract:
A review, Methods in Molecular Biology 268
(2004): 491–502.
2. O. Adolfsson, S. N. Meydani, and R. M.
Russell, Yogurt and gut function, American
245–256.
3. C. C. Chen and W. A. Walker, Probiotics and
prebiotics: Role in clinical disease states,
Advances in Pediatrics 52 (2005): 77–113; M.
E. Sanders, Probiotics: Considerations for
human health, Nutrition Reviews 61 (2003):
91–99; M. H. Floch and J. Hong-Curtiss,
Probiotics and functional foods in gastroin-
testinal disorders, Current Gastroenterology
Reports 3 (2001): 343–350; Probiotics and
prebiotics, American Journal of Clinical Nutri-
tion (supp.) 73 (2001): entire issue.
4. S. Santosa, E. Farnworth, and P. J. H. Jones,
Probiotics and their potential health claims,
Nutrition Reviews 64 (2006): 265–274; S. J.
Salminen, M. Gueimonde, and E. Isolauri,
Probiotics that modify disease risk, American
Society for Nutritional Sciences 135 (2005):
1294–1298; F. Guarner and coauthors,
Should yoghurt cultures be considered
probiotic? British Journal of Nutrition 93
(2005): 783–786; J. M. Saavedra and A.
Tschernia, Human studies with probiotics
and prebiotics: Clinical implications, British
Journal of Nutrition 87 (2002): S241–S246; P.
Marteau and M. C. Boutron-Ruault, Nutri-
tional advantages of probiotics and prebi-
otics, British Journal of Nutrition 87 (2002):
S153–S157; G. T. Macfarlane and J. H. Cum-
mings, Probiotics, infection and immunity,
Current Opinion in Infectious Diseases 15
(2002): 501–506; L. Kopp-Hoolihan, Prophy-
lactic and therapeutic uses of probiotics: A
review, Journal of the American Dietetic Associ-
ation 101 (2001): 229–238; M. B. Roberfroid,
Prebiotics and probiotics: Are they func-
tional foods? American Journal of Clinical
Nutrition 71 (2000): 1682S–1687S.
5. J. Ezendam and H. van Loveren, Probiotics:
Immunomodulation and evaluation of
safety and efficacy, Nutrition Reviews 64
(2006): 1–14.
6. J. M. Wong and coauthors, Colonic health:
Fermentation and short chain fatty acids,
Journal of Clinical Gastroenterology 40 (2006):
235–243; S. Bengmark, Colonic food: Pre-
and probiotics, American Journal of Gastroen-
terology 95 (2000): S5–S7.
7. P. Bourlioux and coauthors, The intestine
and its microflora are partners for the pro-
tection of the host: Report on the Danone
Symposium “The Intelligent Intestine,” held
in Paris, June 14, 2002, American Journal of
REFERENCES
1. c 2. c 3. a 4. d 5. b 6. c 7. b 8. d
9. c 10. c
ANSWERS

HIGHLIGHT 3
Common Digestive Problems
The facts of anatomy and physiology pre-
sented in Chapter 3 permit easy understand-
ing of some common problems that
occasionally arise in the digestive tract. Food
may slip into the air passages instead of the
esophagus, causing choking. Bowel move-
ments may be loose and watery, as in diar-
rhea, or painful and hard, as in constipation.
Some people complain about belching, while others are bothered
by intestinal gas. Sometimes people develop medical problems
such as an ulcer. This highlight describes some of the symptoms
of these common digestive problems and suggests strategies for
preventing them (the glossary on p. 94 defines the relevant
terms).
Choking
A person chokes when a piece of food slips into the trachea and
becomes lodged so securely that it cuts off breathing (see Figure
H3-1). Without oxygen, the person may suffer brain damage or
die. For this reason, it is imperative that everyone learns to recog-
nize a person grabbing his or her own throat as the international
signal for choking (shown in Figure H3-2) and act promptly.
The choking scenario might read like this.
A person is dining in a restaurant with friends.
A chunk of food, usually meat, becomes
lodged in his trachea so firmly that he cannot
make a sound. No sound can be made be-
cause the larynx is in the trachea and makes
sounds only when air is pushed across it. Of-
ten he chooses to suffer alone rather than
“make a scene in public.” If he tries to communicate distress to
his friends, he must depend on pantomime. The friends are bewil-
dered by his antics and become terribly worried when he “faints”
after a few minutes without air. They call for an ambulance, but
by the time it arrives, he is dead from suffocation.
To help a person who is choking, first ask this critical question:
“Can you make any sound at all?” If so, relax. You have time to
decide what you can do to help. Whatever you do, do not hit him
on the back—the particle may become lodged more firmly in his
air passage. If the person cannot make a sound, shout for help
and perform the Heimlich maneuver (described in Figure H3-
2). You would do well to take a life-saving course and practice
these techniques because you will have no time for hesitation if
you are called upon to perform this death-defying act.
Almost any food can cause choking, although some are cited
more often than others: chunks of meat, hot dogs, nuts, whole
grapes, raw carrots, marshmallows, hard or
sticky candies, gum, popcorn, and peanut but-
ter. These foods are particularly difficult for
young children to safely chew and swallow. In
2000, more than 17,500 children (under 15
years old) in the United States choked; most of
them choked on food, and 160 of them choked
to death.1 Always remain alert to the dangers of
choking whenever young children are eating. To
prevent choking, cut food into small pieces,
chew thoroughly before swallowing, don’t talk
or laugh with food in your mouth, and don’t eat
when breathing hard.
Vomiting
Another common digestive mishap is vomiting.
Vomiting can be a symptom of many different
diseases or may arise in situations that upset the
body’s equilibrium, such as air or sea travel. For
whatever reason, the contents of the stomach are
propelled up through the esophagus to the
mouth and expelled.
Tongue
Food
Larynx rises Esophagus
(to stomach)
Trachea
(to lungs)
Epiglottis closes
over larynx
Swallowing. The epiglottis closes
over the larynx, blocking entrance
to the lungs via the trachea. The red
arrow shows that food is heading
down the esophagus normally.
Choking. A choking person cannot
speak or gasp because food lodged
in the trachea blocks the passage of
air. The red arrow points to where
the food should have gone to
prevent choking.
FIGURE H3-1 Normal Swallowing and Choking
92
©
Corbis

If vomiting continues long enough or is severe enough, the
muscular contractions will extend beyond the stomach and carry
the contents of the duodenum, with its green bile, into the stom-
ach and then up the esophagus. Although certainly unpleasant
and wearying for the nauseated person, vomiting such as this is
no cause for alarm. Vomiting is one of the body’s adaptive mech-
anisms to rid itself of something irritating. The best advice is to
rest and drink small amounts of liquids as tolerated until the nau-
sea subsides.
A physician’s care may be needed, however, when large quan-
tities of fluid are lost from the GI tract, causing dehydration. With
massive fluid loss from the GI tract, all of the body’s other fluids
redistribute themselves so that, eventually, fluid is taken from
every cell of the body. Leaving the cells with the fluid are salts that
are absolutely essential to the life of the cells, and they must be re-
placed. Replacement is difficult if the vomiting continues, and in-
travenous feedings of saline and glucose may be necessary while
the physician diagnoses the cause of the vomiting and begins
corrective therapy.
In an infant, vomiting is likely to become serious early in its
course, and a physician should be contacted soon after onset. In-
fants have more fluid between their body cells than adults do, so
more fluid can move readily into the digestive tract and be lost
from the body. Consequently, the body water of infants becomes
depleted and their body salt balance upset faster than in adults.
Self-induced vomiting, such as occurs in
bulimia nervosa, also has serious conse-
quences. In addition to fluid and salt imbal-
ances, repeated vomiting can cause
irritation and infection of the pharynx,
esophagus, and salivary glands; erosion of
the teeth and gums; and dental caries. The
esophagus may rupture or tear, as may the
stomach. Sometimes the eyes become red
from pressure during vomiting. Bulimic be-
havior reflects underlying psychological
problems that require intervention. (Bulimia
nervosa is discussed fully in Highlight 8.)
Projectile vomiting is also serious. The
contents of the stomach are expelled with
such force that they leave the mouth in a
wide arc like a bullet leaving a gun. This
type of vomiting requires immediate med-
ical attention.
Diarrhea
Diarrhea is characterized by frequent,
loose, watery stools. Such stools indicate
that the intestinal contents have moved
too quickly through the intestines for fluid
absorption to take place, or that water has
been drawn from the cells lining the intes-
tinal tract and added to the food residue.
Like vomiting, diarrhea can lead to consid-
erable fluid and salt losses, but the compo-
sition of the fluids is different. Stomach fluids lost in vomiting are
highly acidic, whereas intestinal fluids lost in diarrhea are nearly
neutral. When fluid losses require medical attention, correct re-
placement is crucial.
Diarrhea is a symptom of various medical conditions and treat-
ments. It may occur abruptly in a healthy person as a result of in-
fections (such as food poisoning) or as a side effect of
medications. When used in large quantities, food ingredients
such as the sugar alternative sorbitol and the fat alternative
olestra may also cause diarrhea in some people. If a food is re-
sponsible, then that food must be omitted from the diet, at least
temporarily. If medication is responsible, a different medicine,
when possible, or a different form (injectable versus oral, for ex-
ample) may alleviate the problem.
Diarrhea may also occur as a result of disorders of the GI tract,
such as irritable bowel syndrome or colitis. Irritable bowel syn-
drome is one of the most common GI disorders and is character-
ized by a disturbance in the motility of the GI tract.2 In most
cases, GI contractions are stronger and last longer than normal,
forcing intestinal contents through quickly and causing gas,
bloating, and diarrhea. In some cases, however, GI contractions
are weaker than normal, slowing the passage of intestinal con-
tents and causing constipation. The exact cause of irritable bowel
syndrome is not known, but researchers believe nerves and hor-
mones are involved. The condition seems to worsen for some
The universal signal for choking is when a
person grabs his throat. It alerts others to
the need for assistance. If this happens,
stand behind the person, and wrap your
arms around him. Place the thumb side of
one fist snugly against his body, slightly
above the navel and below the rib cage.
Grasp your fist with your other hand and
give him a sudden strong hug inward and
upward. Repeat thrusts as necessary.
If you are choking and need to
self-administer first aid, place the thumb
side of one fist slightly above your navel
and below your rib cage, grasp the fist with
your other hand, and then press inward and
upward with a quick motion. If this is
unsuccessful, quickly press your upper
abdomen over any firm surface such as the
back of a chair, a countertop, or a railing.
FIGURE H3-2 First Aid for Choking
The first-aid strategy most likely to succeed is abdominal thrusts, sometimes called
the Heimlich maneuver. Only if all else fails, open the person’s mouth by grasping
both his tongue and lower jaw and lifting. Then, and only if you can see the object,
use your finger to sweep it out and begin rescue breathing.
COMMON DIGESTIVE PROBLEMS • 93

may have them three times a week. The symptoms of constipa-
tion include straining during bowel movements, hard stools, and
infrequent bowel movements (fewer than three per week).4 Ab-
94 • Highlight 3
GLOSSARY
acid controllers: medications
used to prevent or relieve
indigestion by suppressing
production of acid in the
stomach; also called H2
blockers. Common brands
include Pepcid AC, Tagamet HB,
Zantac 75, and Axid AR.
antacids: medications used to
relieve indigestion by
neutralizing acid in the
stomach. Common brands
include Alka-Seltzer, Maalox,
Rolaids, and Tums.
belching: the expulsion of gas
from the stomach through the
mouth.
colitis (ko-LYE-tis): inflammation
of the colon.
colonic irrigation: the popular,
but potentially harmful practice
of “washing” the large intestine
with a powerful enema
machine.
constipation: the condition of
having infrequent or difficult
bowel movements.
defecate (DEF-uh-cate): to move
the bowels and eliminate waste.
• defaecare to remove dregs
diarrhea: the frequent passage of
watery bowel movements.
diverticula (dye-ver-TIC-you-la):
sacs or pouches that develop in
the weakened areas of the
intestinal wall (like bulges in an
inner tube where the tire wall
is weak).
• divertir to turn aside
diverticulitis (DYE-ver-tic-you-
LYE-tis): infected or inflamed
diverticula.
• itis infection or
inflammation
diverticulosis (DYE-ver-tic-you-
LOH-sis): the condition of
having diverticula. About one in
every six people in Western
countries develops diverticulosis
in middle or later life.
• osis condition
enemas: solutions inserted into
the rectum and colon to
stimulate a bowel movement
and empty the lower large
intestine.
gastroesophageal reflux: the
backflow of stomach acid into
the esophagus, causing damage
to the cells of the esophagus and
the sensation of heartburn.
Gastroesophageal reflux
disease (GERD) is characterized
by symptoms of reflux occurring
two or more times a week.
heartburn: a burning sensation in
the chest area caused by
backflow of stomach acid into
the esophagus.
Heimlich (HIME-lick) maneuver
(abdominal thrust maneuver):
a technique for dislodging an
object from the trachea of a
choking person (see Figure
H3-2); named for the physician
who developed it.
hemorrhoids (HEM-oh-royds):
painful swelling of the veins
surrounding the rectum.
hiccups (HICK-ups): repeated
cough-like sounds and jerks that
are produced when an involun-
tary spasm of the diaphragm
muscle sucks air down the
windpipe; also spelled hiccoughs.
indigestion: incomplete or
uncomfortable digestion, usually
accompanied by pain, nausea,
vomiting, heartburn, intestinal
gas, or belching.
• in not
irritable bowel syndrome: an
intestinal disorder of unknown
cause. Symptoms include
abdominal discomfort and
cramping, diarrhea,
constipation, or alternating
diarrhea and constipation.
larynx: the upper part of the air
passageway that contains the
vocal cords; also called the voice
box (see Figure H3-1).
laxatives: substances that loosen
the bowels and thereby prevent
or treat constipation.
mineral oil: a purified liquid
derived from petroleum and
used to treat constipation.
peptic ulcer: a lesion in the
mucous membrane of either the
stomach (a gastric ulcer) or the
duodenum (a duodenal ulcer).
• peptic concerning
digestion
trachea (TRAKE-ee-uh): the air
passageway from the larynx to the
lungs; also called the windpipe.
ulcer: a lesion of the skin
or mucous membranes
characterized by inflammation
and damaged tissues. See also
peptic ulcer.
vomiting: expulsion of the
contents of the stomach up
through the esophagus to the
mouth.
Personal hygiene (such as regular hand washing with soap and
water) and safe food preparation (as described in Highlight 18) are
easy and effective steps to take in preventing diarrheal diseases.
people when they eat certain foods or during stressful events.
These triggers seem to aggravate symptoms but not cause them.
Dietary treatment hinges on identifying and avoiding individual
foods that aggravate symptoms; small meals may also be benefi-
cial. People with colitis, an inflammation of the large intestine,
may also suffer from severe diarrhea. They often benefit from
complete bowel rest and medication. If treatment fails, surgery to
remove the colon and rectum may be necessary.
Treatment for diarrhea depends on cause and severity, but it al-
ways begins with rehydration.3 Mild diarrhea may subside with
simple rest and extra liquids (such as clear juices and soups) to re-
place fluid losses. However, call a physician if diarrhea is bloody or
if it worsens or persists—especially in an infant, young child, eld-
erly person, or person with a compromised immune system. Se-
vere diarrhea can be life threatening.
Constipation
Like diarrhea, constipation describes a symptom, not a disease.
Each person’s GI tract has its own cycle of waste elimination,
which depends on its owner’s health, the type of food eaten,
when it was eaten, and when the person takes time to defecate.
What’s normal for some people may not be normal for others.
Some people have bowel movements three times a day; others
©
Ariel
Skelley/Corbis

dominal discomfort, headaches, backaches, and the passing of
gas sometimes accompany constipation.
Often a person’s lifestyle may cause constipation. Being too
busy to respond to the defecation signal is a common complaint.
If a person receives the signal to defecate and ignores it, the sig-
nal may not return for several hours. In the meantime, water con-
tinues to be withdrawn from the fecal matter, so when the person
does defecate, the stools are dry and hard. In such a case, a per-
son’s daily regimen may need to be revised to allow time to have
a bowel movement when the body sends its signal. One possibil-
ity is to go to bed earlier in order to rise earlier, allowing ample
time for a leisurely breakfast and a movement.
Although constipation usually reflects lifestyle habits, in some
cases it may be a side effect of medication or may reflect a med-
ical problem such as tumors that are obstructing the passage of
waste. If discomfort is associated with passing fecal matter, seek
medical advice to rule out disease. Once this has been done, di-
etary or other measures for correction can be considered.
One dietary measure that may be appropriate is to increase di-
etary fiber to 20 to 25 grams per day over the course of a week or
two. Fibers found in fruits, vegetables, and whole grains help to
prevent constipation by increasing fecal mass. In the GI tract, fiber
attracts water, creating soft, bulky stools that stimulate bowel con-
tractions to push the contents along. These contractions
strengthen the intestinal muscles. The improved muscle tone, to-
gether with the water content of the stools, eases elimination, re-
ducing the pressure in the rectal veins and helping to prevent
hemorrhoids. Chapter 4 provides more information on fiber’s
role in maintaining a healthy colon and reducing the risks of colon
cancer and diverticulosis. Diverticulosis is a condition in which
the intestinal walls develop bulges in weakened areas, most com-
monly in the colon (see Figure H3-3). These bulging pockets,
known as diverticula, can worsen constipation, entrap feces, and
become painfully infected and inflamed (diverticulitis). Treat-
ment may require hospitalization, antibiotics, or surgery.
Drinking plenty of water in conjunction with eating high-fiber
foods also helps to prevent constipation. The increased bulk phys-
ically stimulates the upper GI tract, promoting peristalsis through-
out. Similarly, physical activity improves the muscle tone and
motility of the digestive tract. As little as 30 minutes of physical
activity a day can help prevent or alleviate constipation.
Eating prunes—or “dried plums” as some have renamed
them—can also be helpful. Prunes are high in fiber and also con-
tain a laxative substance.* If a morning defecation is desired, a
person can drink prune juice at bedtime; if the evening is pre-
ferred, the person can drink prune juice with breakfast.
These suggested changes in lifestyle or diet should correct
chronic constipation without the use of laxatives, enemas, or
mineral oil, although television commercials often try to per-
suade people otherwise. One of the fallacies often perpetrated by
advertisements is that one person’s successful use of a product is
a good recommendation for others to use that product.
As a matter of fact, diet changes that relieve constipation for
one person may increase the constipation of another. For in-
stance, increasing fiber intake stimulates peristalsis and helps the
person with a sluggish colon. Some people, though, have a spas-
tic type of constipation, in which peristalsis promotes strong con-
tractions that close off a segment of the colon and prevent
passage; for these people, increasing fiber intake would be ex-
actly the wrong thing to do.
A person who seems to need products such as laxatives fre-
quently should seek a physician’s advice. One potentially harmful
but currently popular practice is colonic irrigation—the inter-
nal washing of the large intestine with a powerful enema ma-
chine. Such an extreme cleansing is not only unnecessary, but it
can be hazardous, causing illness and death from equipment con-
tamination, electrolyte depletion, and intestinal perforation. Less
extreme practices can cause problems, too. Frequent use of laxa-
tives and enemas can lead to dependency; upset the body’s fluid,
salt, and mineral balances; and, in the case of mineral oil, interfere
with the absorption of fat-soluble vitamins. (Mineral oil dissolves
the vitamins but is not itself absorbed. Instead, it leaves the body,
carrying the vitamins with it.)
Belching and Gas
Many people complain of problems that they attribute to exces-
sive gas. For some, belching is the complaint. Others blame in-
testinal gas for abdominal discomforts and embarrassment. Most
people believe that the problems occur after they eat certain
foods. This may be the case with intestinal gas, but belching re-
sults from swallowing air. The best advice for belching seems to
be to eat slowly, chew thoroughly, and relax while eating.
Everyone swallows a little bit of air with each mouthful of food,
but people who eat too fast may swallow too much air and then
have to belch. Ill-fitting dentures, carbonated beverages, and
chewing gum can also contribute to the swallowing of air with re-
sultant belching. Occasionally, belching can be a sign of a more
serious disorder, such as gallbladder disease or a peptic ulcer.
Diverticula
(plural)
Diverticulum
(singular)
FIGURE H3-3 Diverticula in the Colon
Diverticula may develop anywhere along the GI tract, but
they are most common in the colon.
* This substance is dihydroxyphenyl isatin.

People who eat or drink too fast may also trigger hiccups, the
repeated spasms that produce a cough-like sound and jerky
movement. Normally, hiccups soon subside and are of no med-
ical significance, but they can be bothersome. The most effective
cure is to hold the breath for as long as possible, which helps to
relieve the spasms of the diaphragm.
Although expelling gas can be a humiliating experience, it is
quite normal. (People who experience painful bloating from mal-
absorption diseases, however, require medical treatment.)
Healthy people expel several hundred milliliters of gas several
times a day. Almost all (99 percent) of the gases expelled—nitro-
gen, oxygen, hydrogen, methane, and carbon dioxide—are
odorless. The remaining “volatile” gases are the infamous ones.
Foods that produce gas usually must be determined individu-
ally. The most common offenders are foods rich in the carbohy-
drates—sugars, starches, and fibers. When partially digested
carbohydrates reach the large intestine, bacteria digest them, giv-
ing off gas as a by-product. People can test foods suspected of
forming gas by omitting them individually for a trial period to see
if there is any improvement.
Heartburn and “Acid
Indigestion”
Almost everyone has experienced heartburn at one time or
another, usually soon after eating a meal. Medically known as
gastroesophageal reflux, heartburn is the painful sensation
a person feels behind the breastbone when the lower
esophageal sphincter allows the stomach contents to reflux into
the esophagus (see Figure H3-4). This may happen if a person
eats or drinks too much (or both). Tight clothing and even
changes of position (lying down, bending over) can cause it,
too, as can some medications and smoking. Weight gain and
overweight increase the frequency, severity, and duration of
heartburn symptoms.5 A defect of the sphincter muscle itself is
a possible, but less common, cause.
If the heartburn is not caused by an
anatomical defect, treatment is fairly
simple. To avoid such misery in the fu-
ture, the person needs to learn to eat
less at a sitting, chew food more thor-
oughly, and eat it more slowly. Addi-
tional strategies are presented in Table
H3-1 at the end of this highlight.
As far as “acid indigestion” is con-
cerned, recall from Chapter 3 that the
strong acidity of the stomach is a desir-
able condition—television commercials
for antacids and acid controllers
notwithstanding. People who overeat
or eat too quickly are likely to suffer
from indigestion. The muscular reac-
tion of the stomach to unchewed
lumps or to being overfilled may be so
violent that it upsets normal peristalsis.
When this happens, overeaters may
taste the stomach acid and feel pain.
Responding to advertisements, they
may reach for antacids or acid con-
trollers. Both of these drugs were orig-
inally designed to treat GI illnesses such
as ulcers. As is true of most over-the-
counter medicines, antacids and acid
96 • Highlight 3
People troubled by gas need to determine which foods bother them
and then eat those foods in moderation.
Stomach
Diaphragm
Acidic stomach contents
Weakened lower
esophageal sphincter
Esophagus
Reflux
FIGURE H3-4 Gastroesophageal Reflux
©
Polara
Studios
Inc.

controllers should be used only infrequently for occasional heart-
burn; they may mask or cause problems if used regularly. Acid-
blocking drugs weaken the defensive mucous barrier of the GI
tract, thereby increasing the risks of infections such as pneumo-
nia, especially in vulnerable populations like the elderly.6 Instead
of self-medicating, people who suffer from frequent and regular
bouts of heartburn and indigestion should try the strategies
presented in the table below. If problems continue, they may
need to see a physician, who can prescribe specific medication
to control gastroesophageal reflux. Without treatment, the re-
peated splashes of acid can severely damage the cells of the
esophagus, creating a condition known as Barrett’s esophagus.7
At that stage, the risk of cancer in the throat or esophagus in-
creases dramatically. To repeat, if symptoms persist, see a doc-
tor—don’t self-medicate.
Ulcers
Ulcers are another common digestive problem. An ulcer is a le-
sion (a sore) and a peptic ulcer is a lesion in the lining of the
stomach (gastric ulcers) or the duodenum of the small intestine
(duodenal ulcers). The compromised lining is left unprotected
and exposed to gastric juices, which can be painful. In some
cases, ulcers can cause internal bleeding. If GI bleeding is exces-
sive, iron deficiency may develop. Ulcers that perforate the GI lin-
ing can pose life-threatening complications.
Many people naively believe that an ulcer is caused by stress or
spicy foods, but this is not the case. The stomach lining in a
healthy person is well protected by its mucous coat. What, then,
causes ulcers to form?
Three major causes of ulcers have been identified: bacterial in-
fection with Helicobacter pylori (commonly abbreviated H. pylori);
the use of certain anti-inflammatory drugs such as aspirin, ibupro-
fen, and naproxen; and disorders that cause excessive gastric acid
secretion. Most commonly, ulcers develop in response to H. pylori
infection.8 The cause of the ulcer dictates the type of medication
used in treatment. For example, people with ulcers caused by in-
fection receive antibiotics, whereas those with ulcers caused by
medicines discontinue their use. In addition, all treatment plans
aim to relieve pain, heal the ulcer, and prevent recurrence.
The regimen for ulcer treatment is to treat for infection, elimi-
nate any food that routinely causes indigestion or pain, and avoid
coffee and caffeine- and alcohol-containing beverages. Both reg-
ular and decaffeinated coffee stimulate acid secretion and so ag-
gravate existing ulcers.
Ulcers and their treatments highlight the importance of not
self-medicating when symptoms persist. People with H. pylori in-
fection often take over-the-counter acid controllers to relieve the
pain of their ulcers when, instead, they need physician-prescribed
antibiotics. Suppressing gastric acidity not only fails to heal the ul-
cer, but it also actually worsens inflammation during an H. pylori
infection. Furthermore, H. pylori infection has been linked with
stomach cancer, making prompt diagnosis and appropriate treat-
ment essential.9
Table H3-1 summarizes strategies to prevent or alleviate common
GI problems. Many of these problems reflect hurried lifestyles. For
this reason, many of their remedies require that people slow
down and take the time to eat leisurely; chew food thoroughly to
prevent choking, heartburn, and acid indigestion; rest until vom-
iting and diarrhea subside; and heed the urge to defecate. In ad-
dition, people must learn how to handle life’s day-to-day
problems and challenges without overreacting and becoming up-
set; learn how to relax, get enough sleep, and enjoy life. Remem-
ber, “what’s eating you” may cause more GI distress than what
you eat.
TABLE H3-1 Strategies to Prevent or Alleviate Common GI Problems
GI Problem Strategies
Choking • Take small bites of food.
• Chew thoroughly before swallowing.
• Don’t talk or laugh with food in your mouth.
• Don’t eat when breathing hard.
Diarrhea • Rest.
• Drink fluids to replace losses.
• Call for medical help if diarrhea persists.
Constipation • Eat a high-fiber diet.
• Drink plenty of fluids.
• Exercise regularly.
• Respond promptly to the urge to defecate.
Belching • Eat slowly.
• Chew thoroughly.
• Relax while eating.
Intestinal gas • Eat bothersome foods in moderation.
GI Problem Strategies
Heartburn • Eat small meals.
• Drink liquids between meals.
• Sit up while eating; elevate your head when
lying down.
• Wait 3 hours after eating before lying down.
• Wait 2 hours after eating before exercising.
• Refrain from wearing tight-fitting clothing.
• Avoid foods, beverages, and medications that
aggravate your heartburn.
• Refrain from smoking cigarettes or using
tobacco products.
• Lose weight if overweight.
Ulcer • Take medicine as prescribed by your physician.
• Avoid coffee and caffeine- and alcohol-
containing beverages.
• Avoid foods that aggravate your ulcer.
• Minimize aspirin, ibuprofen, and naproxen use.
• Refrain from smoking cigarettes.

98 • Highlight 3
• Search for “choking,” “vomiting,” “diarrhea,” “constipa-
tion,” “heartburn,” “indigestion,” and “ulcers” at the U.S.
Government health information site:
www.healthfinder.gov
• Visit the Center for Digestive Health and Nutrition:
www.gihealth.com
• Visit the Digestive Diseases section of the National Insti-
tute of Diabetes, Digestive, and Kidney Diseases:
www.niddk.nih.gov/health/health.htm
• Visit the patient information section of the American
College of Gastroenterology: www.acg.gi.org
• Learn more about H. pylori from the Helicobacter Founda-
tion: www.helico.com
1. K. Gotsch, J. L. Annest, and P. Holmgreen,
Nonfatal choking-related episodes among
children-United States, 2001, Morbidity and
Mortality Weekly Report 51 (2002): 945–948.
2. B. J. Horwitz and R. S. Fisher, The irritable
bowel syndrome, New England Journal of
Medicine 344 (2001): 1846–1850.
3. N. M. Thielman and R. L. Guerrant, Acute
infectious diarrhea, New England Journal of
Medicine 350 (2004): 38–47.
4. A. Lembo and M. Camilleri, Chronic consti-
pation, New England Journal of Medicine 349
(2003): 1360–1368.
5. B. C. Jacobson and coauthors, Body-mass
index and symptoms of gastroesophageal
reflux in women, New England Journal of
Medicine 354 (2006): 2340–2348.
6. R. J. F. Laheij and coauthors, Risk of commu-
nity-acquired pneumonia and use of gastric
acid-suppressive drugs, Journal of the American
7. N. Shaheen and D. F. Ransohoff, Gastro-
esophageal reflux, Barrett’s esophagus, and
esophageal cancer: Scientific review, Journal
(2002): 1972–1981.
8. S. Suerbaum and P. Michetti, Helicobacter
pylori infection, New England Journal of
Medicine 347 (2002): 1175–1186.
9. N. Uemura and coauthors, Helicobacter
pylori infection and the development of
gastric cancer, New England Journal of Medi-
cine 345 (2001): 784–789.
REFERENCES

Whether you are cramming for an exam or daydreaming about your next
vacation, your brain needs carbohydrate to power its activities. Your muscles
need carbohydrate to fuel their work, too, whether you are racing up the
stairs to class or moving on the dance floor to your favorite music. Where can
you get carbohydrate? And are some foods healthier choices than others? As
you will learn from this chapter, whole grains, vegetables, legumes, and fruits
naturally deliver ample carbohydrate and fiber with valuable vitamins and
minerals and little or no fat. Milk products typically lack fiber, but they also
provide carbohydrate along with an assortment of vitamins and minerals.
The CengageNOW logo
Figure 4.10: Animated! Carbohydrate Digestion
in the GI Tract
Kevin Summers/Getty Images

A student, quietly studying a textbook, is seldom aware that within his brain
cells, billions of glucose molecules are splitting to provide the energy that per-
mits him to learn. Yet glucose provides nearly all of the energy the human
brain uses daily. Similarly, a marathon runner, bursting across the finish line in
an explosion of sweat and triumph, seldom gives credit to the glycogen fuel her
muscles have devoured to help her finish the race. Yet, together, these two car-
bohydrates—glucose and its storage form glycogen—provide about half of all
the energy muscles and other body tissues use. The other half of the body’s en-
ergy comes mostly from fat.
People don’t eat glucose and glycogen directly. When they eat foods
rich in carbohydrates, their bodies receive glucose for immediate energy
and into glycogen for reserve energy. All plant foods—whole grains, veg-
etables, legumes, and fruits—provide ample carbohydrate. Milk also con-
tains carbohydrates.
Many people mistakenly think of carbohydrates as “fattening” and avoid
them when trying to lose weight. Such a strategy may be helpful if the car-
bohydrates are the simple sugars of soft drinks, candy, and cookies, but it is
counterproductive if the carbohydrates are the complex carbohydrates of
whole grains, vegetables, and legumes. As the next section explains, not all
carbohydrates are created equal.
The Chemist’s View of Carbohydrates
The dietary carbohydrate family includes the simple carbohydrates (the sugars)
and the complex carbohydrates (the starches and fibers). The simple carbohy-
drates are those that chemists describe as:
• Monosaccharides—single sugars
• Disaccharides—sugars composed of pairs of monosaccharides
The complex carbohydrates are:
• Polysaccharides—large molecules composed of chains of monosaccharides
101
CHAPTER OUTLINE
The Chemist’s View of
Carbohydrates
The Simple Carbohydrates •
Monosaccharides • Disaccharides
The Complex Carbohydrates •
Glycogen • Starches • Fibers
Digestion and Absorption of
Carbohydrates • Carbohydrate
Digestion • Carbohydrate Absorption •
Lactose Intolerance
Glucose in the Body • A Preview of
Carbohydrate Metabolism • The Con-
stancy of Blood Glucose
Health Effects and Recommended
Intakes of Sugars • Health Effects
of Sugars • Controversies Surrounding
Sugars • Recommended Intakes of Sugars
Intakes of Starch and Fibers •
Health Effects of Starch and Fibers •
Recommended Intakes of Starch and
Fibers • From Guidelines to Groceries
HIGHLIGHT 4 Alternatives to Sugar
4
The Carbohydrates:
Sugars, Starches,
and Fibers
C H A P T E R
carbohydrates: compounds composed of
carbon, oxygen, and hydrogen arranged
as monosaccharides or multiples of
monosaccharides. Most, but not all,
carbohydrates have a ratio of one carbon
molecule to one water molecule: (CH2O)n.
• carbo = carbon (C)
• hydrate = with water (H2O)
simple carbohydrates (sugars):
monosaccharides and disaccharides.
complex carbohydrates (starches and
fibers): polysaccharides composed of
straight or branched chains of
monosaccharides.

102 • CHAPTER 4
To understand the structure of carbohydrates, look at the units of which they are
made. The monosaccharides most important in nutrition ◆ each contain 6 carbon
atoms, 12 hydrogens, and 6 oxygens (written in shorthand as C6H12O6).
Each atom can form a certain number of chemical bonds with other atoms:
• Carbon atoms can form four bonds
• Nitrogen atoms, three
• Oxygen atoms, two
• Hydrogen atoms, only one
Chemists represent the bonds as lines between the chemical symbols (such as C, N,
O, and H) that stand for the atoms (see Figure 4-1).
Atoms form molecules in ways that satisfy the bonding requirements of each
atom. Figure 4-1 includes the structure of ethyl alcohol, the active ingredient of alco-
holic beverages, as an example. The two carbons each have four bonds represented
by lines; the oxygen has two; and each hydrogen has one bond connecting it to other
atoms. Chemical structures bond according to these rules as dictated by nature.
H
1
O
2
N
3
C
4
Each atom has a characteristic number
of bonds it can form with other atoms.
H O
C
Notice that in this simple molecule of
ethyl alcohol, each H has one bond,
O has two, and each C has four.
C H
H H
H H
FIGURE 4-1 Atoms and Their Bonds
The four main types of atoms found in
nutrients are hydrogen (H), oxygen (O),
nitrogen (N), and carbon (C).
The carbohydrates are made of carbon (C), oxygen (O), and hydrogen (H).
Each of these atoms can form a specified number of chemical bonds: carbon
forms four, oxygen forms two, and hydrogen forms one.
IN SUMMARY
The Simple Carbohydrates
The following list of the most important simple carbohydrates in nutrition symbolizes
them as hexagons and pentagons of different colors.* Three are monosaccharides:
• Glucose
• Fructose
• Galactose
Three are disaccharides:
• Maltose (glucose + glucose)
• Sucrose (glucose + fructose)
• Lactose (glucose + galactose)
Monosaccharides
The three monosaccharides important in nutrition all have the same numbers
and kinds of atoms, but in different arrangements. These chemical differences ac-
count for the differing sweetness of the monosaccharides. A pinch of purified glucose
on the tongue gives only a mild sweet flavor, and galactose hardly tastes sweet at all.
Fructose, however, is as intensely sweet as honey and, in fact, is the sugar primarily
responsible for honey’s sweetness.
Glucose Chemically, glucose is a larger and more complicated molecule than the
ethyl alcohol shown in Figure 4-1, but it obeys the same rules of chemistry: each car-
bon atom has four bonds; each oxygen, two bonds; and each hydrogen, one bond.
Figure 4-2 illustrates the chemical structure of a glucose molecule.
The diagram of a glucose molecule shows all the relationships between the
atoms and proves simple on examination, but chemists have adopted even sim-
pler ways to depict chemical structures. Figure 4-3 presents the chemical structure
H
H
O
H
H
O
H
H
H
H
O H
H
O H
O H
C
C
C C
C
C
O
FIGURE 4-2 Chemical Structure of
Glucose
On paper, the structure of glucose has
to be drawn flat, but in nature the five
carbons and oxygen are roughly in a
plane. The atoms attached to the ring
carbons extend above and below the
plane.
* Fructose is shown as a pentagon, but like the other monosaccharides, it has six carbons (as you will
see in Figure 4-4).
◆ Most of the monosaccharides important in
nutrition are hexoses, simple sugars with six
atoms of carbon and the formula C6H12O6.
• hex six
monosaccharides (mon-oh-SACK-uh-rides):
carbohydrates of the general formula
CnH2nOn that typically form a single ring.
See Appendix C for the chemical structures
of the monosaccharides.
• mono = one
• saccharide = sugar
glucose (GLOO-kose): a monosaccharide;
sometimes known as blood sugar or
dextrose.
• ose = carbohydrate
• = glucose

THE CARBOHYDRATES: SUGARS, STARCHES, AND FIBERS • 103
of glucose in a more simplified way by combining or omitting several symbols—
yet it conveys the same information.
Commonly known as blood sugar, glucose serves as an essential energy source
for all the body’s activities. Its significance to nutrition is tremendous. Later sections
explain that glucose is one of the two sugars in every disaccharide and the unit
from which the polysaccharides are made almost exclusively. One of these polysac-
charides, starch, is the chief food source of energy for all the world’s people; an-
other, glycogen, is an important storage form of energy in the body. Glucose
reappears frequently throughout this chapter and all those that follow.
Fructose Fructose is the sweetest of the sugars. Curiously, fructose has exactly the
same chemical formula as glucose—C6H12O6—but its structure differs (see Figure 4-4).
The arrangement of the atoms in fructose stimulates the taste buds on the tongue to
produce the sweet sensation. Fructose occurs naturally in fruits and honey; other
sources include products such as soft drinks, ready-to-eat cereals, and desserts that
have been sweetened with high-fructose corn syrup (defined on p. 118).
Galactose The monosaccharide galactose occurs naturally as a single sugar in
only a few foods. Galactose has the same numbers and kinds of atoms as glucose
and fructose in yet another arrangement. Figure 4-5 shows galactose beside a mole-
cule of glucose for comparison.
Disaccharides
The disaccharides are pairs of the three monosaccharides just described. Glucose
occurs in all three; the second member of the pair is either fructose, galactose, or
OH
OH
OH
HO
CH2OH
O
H H
H
H
H
OH
OH
OH
HO
CH2OH
O O
C C
C
C
C
C
The lines representing some of
the bonds and the carbons at the
corners are not shown.
Now the single hydrogens are not
shown, but lines still extend
upward or downward from the
ring to show where they belong.
Another way to look at glucose is
to notice that its six carbon atoms
are all connected.
In this and other illustrations
throughout this book, glucose is
represented as a blue hexagon.
FIGURE 4-3 Simplified Diagrams of Glucose
OH
OH
OH
HO
CH2OH
O
OH
HO OH
O
HOCH2 CH2OH
1
2
3
4
5
6
1
2
3
4
5
6
Fructose
Glucose
FIGURE 4-4 Two Monosaccharides:
Glucose and Fructose
Can you see the similarities? If you learned the rules in Fig-
ure 4-3, you will be able to “see” 6 carbons (numbered), 12
hydrogens (those shown plus one at the end of each single
line), and 6 oxygens in both these compounds.
OH
OH
OH
CH2OH
O
Glucose
HO
OH
OH
OH
CH2OH
O
Galactose
HO
FIGURE 4-5 Two Monosaccharides:
Glucose and Galactose
Notice the similarities and the difference (highlighted in
red) between glucose and galactose. Both have 6 carbons,
12 hydrogens, and 6 oxygens, but the position of one OH
group differs slightly.
fructose (FRUK-tose or FROOK-tose): a
monosaccharide; sometimes known as fruit
sugar or levulose. Fructose is found
abundantly in fruits, honey, and saps.
• fruct = fruit
• = fructose
galactose (ga-LAK-tose): a monosaccharide;
part of the disaccharide lactose.
• = galactose
disaccharides (dye-SACK-uh-rides): pairs
of monosaccharides linked together. See
Appendix C for the chemical structures of
the disaccharides.
• di = two

104 • CHAPTER 4
another glucose. These carbohydrates—and all the other energy nutrients—are
put together and taken apart by similar chemical reactions: condensation and
hydrolysis.
Condensation To make a disaccharide, a chemical reaction known as conden-
sation links two monosaccharides together (see Figure 4-6). A hydroxyl (OH) group
from one monosaccharide and a hydrogen atom (H) from the other combine to cre-
ate a molecule of water (H2O). The two originally separate monosaccharides link to-
gether with a single oxygen (O).
Hydrolysis To break a disaccharide in two, a chemical reaction known as hydroly-
sis ◆ occurs (see Figure 4-7). A molecule of water splits to provide the H and OH
needed to complete the resulting monosaccharides. Hydrolysis reactions commonly
occur during digestion.
Maltose The disaccharide maltose consists of two glucose units. Maltose is pro-
duced whenever starch breaks down—as happens in human beings during carbohy-
drate digestion. It also occurs during the fermentation process that yields alcohol.
Maltose is only a minor constituent of a few foods, most notably barley.
Sucrose Fructose and glucose together form sucrose. Because the fructose is acces-
sible to the taste receptors, sucrose tastes sweet, accounting for some of the natural
sweetness of fruits, vegetables, and grains. To make table sugar, sucrose is refined from
the juices of sugarcane and sugar beets, then granulated. Depending on the extent to
which it is refined, the product becomes the familiar brown, white, and powdered sug-
ars available at grocery stores.
O
OH
OH
HO
CH2OH
O
OH
OH
OH
O
CH2OH
O
H
H2O
Water
OH
OH
HO
CH2OH
O
OH
OH
OH
CH2OH
O
+
Glucose + glucose Maltose
H2O
Water
OH
The two glucose molecules bond
together with a single O atom to form
the disaccharide maltose.
An OH group from one glucose and
an H atom from another glucose
combine to create a molecule of H2O.
FIGURE 4-6 Condensation of Two Monosaccharides to Form
a Disaccharide
OH
OH
HO
CH2OH
O
OH
OH
OH
CH2OH
O
Maltose Glucose + glucose
OH
OH
HO
CH2OH
O
OH
OH
OH
CH2OH
O
O
OH
H
Bond
broken
Bond broken
+
Water
The disaccharide maltose splits into two glucose molecules with H added to one and OH
to the other (from the water molecule).
OH HO
FIGURE 4-7 Hydrolysis of a Disaccharide
◆ Reminder: A hydrolysis reaction splits a mole-
cule into two, with H added to one and OH
to the other (from water); Chapter 3
explained that hydrolysis reactions break
down molecules during digestion.
Fruits package their simple sugars with fibers,
vitamins, and minerals, making them a sweet
and healthy snack.
condensation: a chemical reaction in which
two reactants combine to yield a larger
product.
maltose (MAWL-tose): a disaccharide
composed of two glucose units; sometimes
known as malt sugar.
• = maltose
sucrose (SUE-krose): a disaccharide
composed of glucose and fructose;
commonly known as table sugar, beet sugar,
or cane sugar. Sucrose also occurs in many
fruits and some vegetables and grains.
• sucro = sugar
• = sucrose
©
Altrendo
Images/Getty
Images

The Complex Carbohydrates
The simple carbohydrates are the sugars just mentioned—the monosaccharides glu-
cose, fructose, and galactose and the disaccharides maltose, sucrose, and lactose. In
contrast, the complex carbohydrates contain many glucose units and, in some
cases, a few other monosaccharides strung together as polysaccharides. Three
types of polysaccharides are important in nutrition: glycogen, starches, and fibers.
Glycogen is a storage form of energy in the animal body; starches play that role
in plants; and fibers provide structure in stems, trunks, roots, leaves, and skins of
plants. Both glycogen and starch are built of glucose units; fibers are composed of
a variety of monosaccharides and other carbohydrate derivatives.
Glycogen
Glycogen is found to only a limited extent in meats and not at all in plants.* For
this reason, food is not a significant source of this carbohydrate. However, glycogen
does perform an important role in the body. The human body stores glucose as
glycogen—many glucose molecules linked together in highly branched chains (see
the left side of Figure 4-8 on p. 106). This arrangement permits rapid hydrolysis.
When the hormonal message “release energy” arrives at the glycogen storage sites
in a liver or muscle cell, enzymes respond by attacking the many branches of glyco-
gen simultaneously, making a surge of glucose available.†
Starches
The human body stores glucose as glycogen, but plant cells store glucose as
starches—long, branched or unbranched chains of hundreds or thousands of glu-
cose molecules linked together (see the middle and right side of Figure 4-8). These gi-
ant starch molecules are packed side by side in grains such as wheat or rice, in root
crops and tubers such as yams and potatoes, and in legumes such as peas and
beans. When you eat the plant, your body hydrolyzes the starch to glucose and uses
the glucose for its own energy purposes.
All starchy foods come from plants. Grains are the richest food source of starch,
providing much of the food energy for people all over the world—rice in Asia;
Six simple carbohydrates, or sugars, are important in nutrition. The three
monosaccharides (glucose, fructose, and galactose) all have the same chemi-
cal formula (C6H12O6), but their structures differ. The three disaccharides
(maltose, sucrose, and lactose) are pairs of monosaccharides, each containing
a glucose paired with one of the three monosaccharides. The sugars derive pri-
marily from plants, except for lactose and its component galactose, which
come from milk and milk products. Two monosaccharides can be linked to-
gether by a condensation reaction to form a disaccharide and water. A disac-
charide, in turn, can be broken into its two monosaccharides by a hydrolysis
reaction using water.
IN SUMMARY
* Glycogen in animal muscles rapidly hydrolyzes after slaughter.
† Normally, only liver cells can produce glucose from glycogen to be sent directly to the blood; muscle
cells can also produce glucose from glycogen, but must use it themselves. Muscle cells can restore the
blood glucose level indirectly, however, as Chapter 7 explains.
Major sources of starch include grains (such as
rice, wheat, millet, rye, barley, and oats),
legumes (such as kidney beans, black-eyed
peas, pinto beans, navy beans, and garbanzo
beans), tubers (such as potatoes), and root
crops (such as yams and cassava).
lactose (LAK-tose): a disaccharide composed
of glucose and galactose; commonly known
as milk sugar.
• lact = milk
• = lactose
polysaccharides: compounds composed of
many monosaccharides linked together.
An intermediate string of three to ten
monosaccharides is an oligosaccharide.
• poly = many
• oligo = few
glycogen (GLY-ko-jen): an animal
polysaccharide composed of glucose;
manufactured and stored in the liver and
muscles as a storage form of glucose.
Glycogen is not a significant food source of
carbohydrate and is not counted as one of
the complex carbohydrates in foods.
• glyco = glucose
• gen = gives rise to
starches: plant polysaccharides composed of
glucose.
©
Polara
Studios
Inc.
Lactose The combination of galactose and glucose makes the disaccharide lactose,
the principal carbohydrate of milk. Known as milk sugar, lactose contributes half of
the energy (kcalories) provided by fat-free milk.

106 • CHAPTER 4
wheat in Canada, the United States, and Europe; corn in much of Central and
South America; and millet, rye, barley, and oats elsewhere. Legumes and tubers are
also important sources of starch.
Fibers
Dietary fibers are the structural parts of plants and thus are found in all plant-
derived foods—vegetables, fruits, whole grains, and legumes. Most dietary fibers are
polysaccharides. As mentioned earlier, starches are also polysacharides, but dietary
fibers differ from starches in that the bonds between their monosaccharides cannot
be broken down by digestive enzymes in the body. For this reason, dietary fibers are
often described as nonstarch polysaccharides.* Figure 4-9 illustrates the difference in
the bonds that link glucose molecules together in starch with those found in the fiber
cellulose. Because dietary fibers pass through the body, they contribute no monosac-
charides, and therefore little or no energy.
Even though most foods contain a variety of fibers, researchers often sort dietary
fibers into two groups according to their solubility. Such distinctions help to explain
their actions in the body.
Soluble Fibers Some dietary fibers dissolve in water (soluble fibers), form gels
(viscous), and are easily digested by bacteria in the colon (fermentable). Com-
monly found in oats, barley, legumes, and citrus fruits, soluble fibers are most often
associated with protecting against heart disease and diabetes by lowering blood
cholesterol and glucose levels, respectively.1
Insoluble Fibers Other fibers do not dissolve in water (insoluble fibers), do not form
gels (nonviscous), and are less readily fermented. Found mostly in whole grains (bran)
and vegetables, insoluble fibers promote bowel movements and alleviate constipation.
Fiber Sources As mentioned, dietary fibers occur naturally in plants. When these
fibers have been extracted from plants or manufactured and then added to foods or
used in supplements they are called functional fibers—if they have beneficial health
Glycogen Starch (amylopectin) Starch (amylose)
A glycogen molecule contains hundreds of
glucose units in highly branched chains. Each
new glycogen molecule needs a special protein
for the attachment of the first glucose (shown
here in red).
A starch molecule contains hundreds of glucose molecules in
either occasionally branched chains (amylopectin) or unbranched
chains (amylose).
FIGURE 4-8 Glycogen and Starch Molecules Compared (Small Segments)
Notice the more highly branched the structure, the greater the number of ends from which glucose can be released. (These units
would have to be magnified millions of times to appear at the size shown in this figure. For details of the chemical structures, see
Appendix C.)
* The nonstarch polysaccharide fibers include cellulose, hemicelluloses, pectins, gums, and mucilages.
Fibers also include some nonpolysaccharides such as lignins, cutins, and tannins.
† Dietary fibers are fermented by bacteria in the colon to short-chain fatty acids, which are absorbed
and metabolized by cells in the GI tract and liver (Chapter 5 describes fatty acids).
dietary fibers: in plant foods, the nonstarch
polysaccharides that are not digested by human
digestive enzymes, although some are digested
by GI tract bacteria. Dietary fibers include
cellulose, hemicelluloses, pectins, gums, and
mucilages and the nonpolysaccharides lignins,
cutins, and tannins.
soluble fibers: indigestible food components
that dissolve in water to form a gel. An
example is pectin from fruit, which is used
to thicken jellies.
viscous: a gel-like consistency.
fermentable: the extent to which bacteria in
the GI tract can break down fibers to
fragments that the body can use.†
insoluble fibers: indigestible food
components that do not dissolve in water.
Examples include the tough, fibrous
structures found in the strings of celery
and the skins of corn kernels.

effects. Cellulose in cereals, for example, is a dietary fiber, but when consumed as a
supplement to alleviate constipation, cellulose is considered a functional fiber. Total
fiber refers to the sum of dietary fibers and functional fibers. These terms ◆ were cre-
ated by the DRI Committee to accommodate products that may contain new fiber
sources, but consumers may find them too confusing to be used on food labels.2
Resistant Starches A few starches are classified as dietary fibers. Known as re-
sistant starches, these starches escape digestion and absorption in the small intes-
tine. Starch may resist digestion for several reasons, including the individual’s
efficiency in digesting starches and the food’s physical properties. Resistant starch is
common in whole legumes, raw potatoes, and unripe bananas.
Phytic Acid Althought not classified as a dietary fiber, phytic acid is often found
accompanying them in the same foods. Because of this close association, re-
searchers have been unable to determine whether it is the dietary fiber, the phytic
acid, or both, that binds with minerals, preventing their absorption. This binding
presents a risk of mineral deficiencies, but the risk is minimal when total fiber intake
is reasonable and mineral intake adequate. The nutrition consequences of such
mineral losses are described further in Chapters 12 and 13.
IN SUMMARY
The complex carbohydrates are the polysaccharides (chains of monosaccha-
rides): glycogen, starches, and dietary fibers. Both glycogen and starch are
storage forms of glucose—glycogen in the body, and starch in plants—and
both yield energy for human use. The dietary fibers also contain glucose (and
other monosaccharides), but their bonds cannot be broken by human diges-
tive enzymes, so they yield little, if any, energy. The accompanying table sum-
marizes the carbohydrate family of compounds.
The Carbohydrate Family
Simple Carbohydrates (Sugars) Complex Carbohydrates
• Monosaccharides: • Polysaccharides:
Glucose Glycogena
Fructose Starches
Galactose Fibers
• Disaccharides:
Maltose
Sucrose
Lactose
aGlycogen is a complex carbohydrate (a polysaccharide) but not a dietary source of carbohydrate.
Digestion and Absorption
of Carbohydrates
The ultimate goal of digestion and absorption of sugars and starches is to break them
into small molecules—chiefly glucose—that the body can absorb and use. The large
starch molecules require extensive breakdown; the disaccharides need only be broken
once and the monosaccharides not at all. The initial splitting begins in the mouth;
the final splitting and absorption occur in the small intestine; and conversion to a
common energy currency (glucose) takes place in the liver. The details follow.
◆ Dietary fibers occur naturally in intact plants.
Functional fibers have been extracted from
plants or manufactured and have beneficial
effects in human beings. Total fiber is the
sum of dietary fibers and functional fibers.
resistant starches: starches that escape
digestion and absorption in the small
intestine of healthy people.
phytic (FYE-tick) acid: a nonnutrient
component of plant seeds; also called
phytate (FYE-tate). Phytic acid occurs in the
husks of grains, legumes, and seeds and is
capable of binding minerals such as zinc,
iron, calcium, magnesium, and copper in
insoluble complexes in the intestine, which
the body excretes unused.
Starch
Cellulose
FIGURE 4-9 Starch and Cellulose Mol-
ecules Compared (Small Segments)
The bonds that link the glucose mole-
cules together in cellulose are different
from the bonds in starch (and glyco-
gen). Human enzymes cannot digest
cellulose. See Appendix C for chemical
structures and descriptions of linkages.

108 • CHAPTER 4
Carbohydrate Digestion
Figure 4-10 traces the digestion of carbohydrates through the GI tract. When a per-
son eats foods containing starch, enzymes hydrolyze the long chains to shorter
chains, ◆ the short chains to disaccharides, and, finally, the disaccharides to mono-
saccharides. This process begins in the mouth.
In the Mouth In the mouth, thoroughly chewing high-fiber foods slows eating and
stimulates the flow of saliva. The salivary enzyme amylase starts to work, hydrolyz-
ing starch to shorter polysaccharides and to the disaccharide maltose. In fact, you
can taste the change if you hold a piece of starchy food like a cracker in your mouth
for a few minutes without swallowing it—the cracker begins tasting sweeter as the
enzyme acts on it. Because food is in the mouth for only a short time, very little car-
bohydrate digestion takes place there; it begins again in the small intestine.
In the Stomach The swallowed bolus ◆ mixes with the stomach’s acid and pro-
tein-digesting enzymes, which inactivate salivary amylase. Thus the role of salivary
amylase in starch digestion is relatively minor. To a small extent, the stomach’s acid
continues breaking down starch, but its juices contain no enzymes to digest carbo-
hydrate. Fibers linger in the stomach and delay gastric emptying, thereby providing
a feeling of fullness and satiety.
In the Small Intestine The small intestine performs most of the work of carbohy-
drate digestion. A major carbohydrate-digesting enzyme, pancreatic amylase, en-
ters the intestine via the pancreatic duct and continues breaking down the
polysaccharides to shorter glucose chains and maltose. The final step takes place
on the outer membranes of the intestinal cells. There specific enzymes ◆ break
down specific disaccharides:
• Maltase breaks maltose into two glucose molecules.
• Sucrase breaks sucrose into one glucose and one fructose molecule.
• Lactase breaks lactose into one glucose and one galactose molecule.
At this point, all polysaccharides and disaccharides have been broken down to
monosaccharides—mostly glucose molecules, with some fructose and galactose
molecules as well.
In the Large Intestine Within one to four hours after a meal, all the sugars and
most of the starches have been digested. ◆ Only the fibers remain in the digestive
tract. Fibers in the large intestine attract water, which softens the stools for passage
without straining. Also, bacteria in the GI tract ferment some fibers. This process
generates water, gas, and short-chain fatty acids (described in Chapter 5).* The
colon uses these small fat molecules for energy. Metabolism of short-chain fatty
acids also occurs in the cells of the liver. Fibers, therefore, can contribute some en-
ergy (1.5 to 2.5 kcalories per gram), depending on the extent to which they are bro-
ken down by bacteria and the fatty acids are absorbed.
Carbohydrate Absorption
Glucose is unique in that it can be absorbed to some extent through the lining of the
mouth, but for the most part, nutrient absorption takes place in the small intestine.
Glucose and galactose traverse the cells lining the small intestine by active trans-
port; fructose is absorbed by facilitated diffusion, which slows its entry and produces
a smaller rise in blood glucose. Likewise, unbranched chains of starch are digested
slowly and produce a smaller rise in blood glucose than branched chains, which
have many more places for enzymes to attack and release glucose rapidly.
As the blood from the intestines circulates through the liver, cells there take up
fructose and galactose and convert them to other compounds, most often to glu-
◆ The short chains of glucose units that result
from the breakdown of starch are known as
dextrins. The word sometimes appears on
food labels because dextrins can be used as
thickening agents in processed foods.
◆ Reminder: A bolus is a portion of food swal-
lowed at one time.
◆ Reminder: In general, the word ending –ase
identifies an enzyme, and the beginning of
the word identifies the molecule that the en-
zyme works on.
◆ Starches and sugars are called available
carbohydrates because human digestive en-
zymes break them down for the body’s use.
In contrast, fibers are called unavailable
carbohydrates because human digestive
enzymes cannot break their bonds.
* The short-chain fatty acids produced by GI bacteria are primarily acetic acid, propionic acid, and
butyric acid.
When a person eats carbohydrate-rich foods,
the body receives a valuable commodity—
glucose.
amylase (AM-ih-lace): an enzyme that
hydrolyzes amylose (a form of starch).
Amylase is a carbohydrase, an enzyme
that breaks down carbohydrates.
satiety (sah-TIE-eh-tee): the feeling of fullness
and satisfaction that occurs after a meal and
inhibits eating until the next meal. Satiety
determines how much time passes between
meals.
• sate = to fill
maltase: an enzyme that hydrolyzes maltose
sucrase: an enzyme that hydrolyzes sucrose
lactase: an enzyme that hydrolyzes lactose
©
Banana
Stock/SuperStock

The pancreas produces an
amylase that is released
through the pancreatic duct
into the small intestine:
Starch
Small
polysac-
charides,
maltose
Pancreatic
amylase
Then disaccharidase enzymes
on the surface of the small
intestinal cells hydrolyze the
disaccharides into
monosaccharides:
Fructose
+
Glucose
Sucrose
Galactose
+
Glucose
Lactose
Maltase
Glucose
+
Glucose
Maltose
Small intestine and pancreas
Sucrase
Lactase
The salivary glands secrete
saliva into the mouth
to moisten the food. The
salivary enzyme amylase
begins digestion:
Starch
Amylase Small
polysaccharides,
maltose
Small intestine
Fiber is not digested, and it
delays absorption of other
nutrients.
Large intestine
Most fiber passes intact through
the digestive tract to the large
intestine. Here, bacterial
enzymes digest fiber:
Some
fiber
Bacterial
enzymes
Short-chain
fatty acids,
gas
Fiber holds water; regulates
bowel activity; and binds
substances such as bile,
cholesterol, and some minerals,
carrying them out of the body.
STARCH FIBER
Mouth
Salivary
glands
(Liver)
(Gallbladder)
Stomach
Pancreas
Small
intestine
Large
intestine
Mouth and salivary glands Mouth
The mechanical action of the
mouth crushes and tears fiber in
food and mixes it with saliva to
moisten it for swallowing.
Stomach
Fiber is not digested, and it
delays gastric emptying.
Intestinal cells absorb these
monosaccharides.
Stomach
Stomach acid inactivates
salivary enzymes, halting
starch digestion.
FIGURE 4-10 Animated! Carbohydrate Digestion in the GI Tract
cose, as shown in Figure 4-11 (p. 110). Thus all disaccharides provide at least one
glucose molecule directly, and they can provide another one indirectly—through
the conversion of fructose and galactose to glucose.
To test your understanding of these concepts, log on to

110 • CHAPTER 4
Small intestine
Monosaccharides, the end products of
carbohydrate digestion, enter the capillaries
of the intestinal villi.
In the liver, galactose
and fructose are
converted to glucose.
Glucose
Fructose
Galactose
Monosaccharides travel to
the liver via the portal vein.
1
2
3
Key:
FIGURE 4-11 Absorption of Monosaccharides
IN SUMMARY
In the digestion and absorption of carbohydrates, the body breaks down
starches into the disaccharide maltose. Maltose and the other disaccharides (lac-
tose and sucrose) from foods are broken down into monosaccharides. Then
monosaccharides are converted mostly to glucose to provide energy for the cells’
work. The fibers help to regulate the passage of food through the GI system and
slow the absorption of glucose, but they contribute little, if any, energy.
Lactose Intolerance
Normally, the intestinal cells produce enough of the enzyme lactase to ensure that
the disaccharide lactose found in milk is both digested and absorbed efficiently. Lac-
tase activity is highest immediately after birth, as befits an infant whose first and
only food for a while will be breast milk or infant formula. In the great majority of
the world’s populations, lactase activity declines dramatically during childhood and
adolescence to about 5 to 10 percent of the activity at birth. Only a relatively small
percentage (about 30 percent) of the people in the world retain enough lactase to di-
gest and absorb lactose efficiently throughout adult life.
Symptoms When more lactose is consumed than the available lactase can han-
dle, lactose molecules remain in the intestine undigested, attracting water and
causing bloating, abdominal discomfort, and diarrhea—the symptoms of lactose
intolerance. The undigested lactose becomes food for intestinal bacteria, which
multiply and produce irritating acid and gas, further contributing to the discom-
fort and diarrhea.
Causes As mentioned, lactase activity commonly declines with age. Lactase de-
ficiency may also develop when the intestinal villi are damaged by disease, certain
medicines, prolonged diarrhea, or malnutrition. Depending on the extent of the in-
testinal damage, lactose malabsorption may be temporary or permanent. In ex-
tremely rare cases, an infant is born with a lactase deficiency.
lactose intolerance: a condition that results
from inability to digest the milk sugar
lactose; characterized by bloating, gas,
abdominal discomfort, and diarrhea. Lactose
intolerance differs from milk allergy, which is
caused by an immune reaction to the
protein in milk.
lactase deficiency: a lack of the enzyme
required to digest the disaccharide lactose
into its component monosaccharides
(glucose and galactose).

Prevalence The prevalence ◆ of lactose intolerance varies widely among ethnic
groups, indicating that the trait is genetically determined. The prevalence of lactose
intolerance is lowest among Scandinavians and other northern Europeans and
highest among native North Americans and Southeast Asians.
Dietary Changes Managing lactose intolerance requires some dietary changes,
although total elimination of milk products usually is not necessary. Excluding all
milk products from the diet can lead to nutrient deficiencies because these foods are
a major source of several nutrients, notably the mineral calcium, vitamin D, and
the B vitamin riboflavin. Fortunately, many people with lactose intolerance can
consume foods containing up to 6 grams of lactose (1/2 cup milk) without symptoms.
The most successful strategies are to increase intake of milk products gradually, take
them with other foods in meals, and spread their intake throughout the day. A
change in the GI bacteria, not the reappearance of the missing enzyme, accounts for
the ability to adapt to milk products. Importantly, most lactose-intolerant individu-
als need to manage their dairy consumption rather than restrict it.3
In many cases, lactose-intolerant people can tolerate fermented milk products
such as yogurt and kefir.4 The bacteria in these products digest lactose for their own
use, thus reducing the lactose content. Even when the lactose content is equivalent
to milk’s, yogurt produces fewer symptoms. Hard cheeses, such as cheddar, and cot-
tage cheese are often well tolerated because most of the lactose is removed with the
whey during manufacturing. Lactose continues to diminish as cheese ages.
Many lactose-intolerant people use commercially prepared milk products that
have been treated with an enzyme that breaks down the lactose. Alternatively, they
take enzyme tablets with meals or add enzyme drops to their milk. The enzyme
hydrolyzes much of the lactose in milk to glucose and galactose, which lactose-
intolerant people can absorb without ill effects.
Because people’s tolerance to lactose varies widely, lactose-restricted diets must
be highly individualized. A completely lactose-free diet can be difficult because lac-
tose appears not only in milk and milk products but also as an ingredient in many
nondairy foods ◆ such as breads, cereals, breakfast drinks, salad dressings, and
cake mixes. People on strict lactose-free diets need to read labels and avoid foods
that include milk, milk solids, whey (milk liquid), and casein (milk protein, which
may contain traces of lactose). They also need to check all medications with the
pharmacist because 20 percent of prescription drugs and 5 percent of over-the-
counter drugs contain lactose as a filler.
People who consume few or no milk products must take care to meet riboflavin,
vitamin D, and calcium needs. Later chapters on the vitamins and minerals offer
help with finding good nonmilk sources of these nutrients.
◆ Estimated prevalence of lactose intolerance:
80% Southeast Asians
80% Native Americans
75% African Americans
70% Mediterranean peoples
60% Inuits
50% Hispanics
20% Caucasians
10% Northern Europeans
◆ Lactose in selected foods:
Whole-wheat bread, 1 slice 0.5 g
Dinner roll, 1 0.5 g
Cheese, 1 oz
Cheddar or American 0.5 g
Parmesan or cream 0.8 g
Doughnut (cake type), 1 1.2 g
Chocolate candy, 1 oz 2.3 g
Sherbet, 1 c 4.0 g
Cottage cheese (low-fat), 1 c 7.5 g
Ice cream, 1 c 9.0 g
Milk, 1 c 12.0 g
Yogurt (low-fat), 1 c 15.0 g
Note: Yogurt is often enriched with nonfat
milk solids, which increase its lactose con-
tent to a level higher than milk’s.
IN SUMMARY
Lactose intolerance is a common condition that occurs when there is insuffi-
cient lactase to digest the disaccharide lactose found in milk and milk prod-
ucts. Symptoms include GI distress. Because treatment requires limiting milk
intake, other sources of riboflavin, vitamin D, and calcium must be included
in the diet.
Glucose in the Body
The primary role of the available carbohydrates in human nutrition is to supply
the body’s cells with glucose for energy. Starch contributes most to the body’s glu-
cose supply, but as explained earlier, any of the monosaccharides can also provide
glucose.
kefir (keh-FUR): a fermented milk created by
adding Lactobacillus acidophilus and other
bacteria that break down lactose to glucose
and galactose, producing a sweet, lactose-
free product.

112 • CHAPTER 4
Scientists have long known that providing energy is glucose’s primary role in the
body, but they have only recently uncovered additional roles that glucose and
other sugars perform in the body.5 ◆ Sugar molecules dangle from many of the
body’s protein and fat molecules, with dramatic consequences. Sugars attached to
a protein change the protein’s shape and function; when they bind to lipids in a
cell’s membranes, sugars alter the way cells recognize each other.6 ◆ Cancer cells
coated with sugar molecules, for example, are able to sneak by the cells of the im-
mune system. Armed with this knowledge, scientists are now trying to use sugar
molecules to create an anticancer vaccine. Further advances in knowledge are sure
to reveal numerous ways these simple, yet remarkable, sugar molecules influence
the health of the body.
A Preview of Carbohydrate Metabolism
Glucose plays the central role in carbohydrate metabolism. This brief discussion
provides just enough information about carbohydrate metabolism to illustrate
that the body needs and uses glucose as a chief energy nutrient. Chapter 7 pro-
vides a full description of energy metabolism.
Storing Glucose as Glycogen The liver stores about one-third of the body’s total
glycogen and releases glucose into the bloodstream as needed. After a meal, blood
glucose rises, and liver cells link the excess glucose molecules by condensation reac-
tions into long, branching chains of glycogen. When blood glucose falls, the liver cells
break glycogen by hydrolysis reactions into single molecules of glucose and release
them into the bloodstream. Thus glucose becomes available to supply energy to the
brain and other tissues regardless of whether the person has eaten recently. Muscle
cells can also store glucose as glycogen (the other two-thirds), but they hoard most of
their supply, using it just for themselves during exercise. The brain maintains a small
amount of glycogen, which is thought to provide an emergency energy reserve during
times of severe glucose deprivation.7
Glycogen holds water and, therefore, is rather bulky. The body can store only
enough glycogen to provide energy for relatively short periods of time—less than a
day during rest and a few hours at most during exercise. For its long-term energy
reserves, for use over days or weeks of food deprivation, the body uses its abundant,
water-free fuel, fat, as Chapter 5 describes.
Using Glucose for Energy Glucose fuels the work of most of the body’s cells. In-
side a cell, enzymes break glucose in half. These halves can be put back together to
make glucose, or they can be further broken down into even smaller fragments
(never again to be reassembled to form glucose). The small fragments can yield en-
ergy when broken down completely to carbon dioxide and water (see Chapter 7).
As mentioned, the liver’s glycogen stores last only for hours, not for days. To keep
providing glucose to meet the body’s energy needs, a person has to eat dietary car-
bohydrate frequently. Yet people who do not always attend faithfully to their bodies’
carbohydrate needs still survive. How do they manage without glucose from dietary
carbohydrate? Do they simply draw energy from the other two energy-yielding nu-
trients, fat and protein? They do draw energy from them, but not simply.
Making Glucose from Protein Glucose is the preferred energy source for brain
cells, other nerve cells, and developing red blood cells. Body protein can be con-
verted to glucose to some extent, but protein has jobs of its own that no other nu-
trient can do. Body fat cannot be converted to glucose to any significant extent.
Thus, when a person does not replenish depleted glycogen stores by eating carbo-
hydrate, body proteins are broken down to make glucose to fuel these special
cells.
The conversion of protein to glucose is called gluconeogenesis—literally, the
making of new glucose. Only adequate dietary carbohydrate can prevent this use
of protein for energy, and this role of carbohydrate is known as its protein-
sparing action.
The carbohydrates of grains, vegetables, fruits,
and legumes supply most of the energy in a
healthful diet.
◆ The study of sugars is known as glycobiology.
◆ These combination molecules are known as
glycoproteins and glycolipids, respectively.
gluconeogenesis (gloo-ko-nee-oh-JEN-ih-
sis): the making of glucose from a
noncarbohydrate source (described in
more detail in Chapter 7).
• gluco = glucose
• neo = new
• genesis = making
protein-sparing action: the action of
carbohydrate (and fat) in providing energy
that allows protein to be used for other
purposes.
©
Brian
Leatart/FoodPix/Jupiter
Images

Making Ketone Bodies from Fat Fragments An inadequate supply of carbo-
hydrate can shift the body’s energy metabolism in a precarious direction. With less
carbohydrate providing glucose to meet the brain’s energy needs, fat takes an alter-
native metabolic pathway; instead of entering the main energy pathway, fat frag-
ments combine with each other, forming ketone bodies. Ketone bodies provide an
alternate fuel source during starvation, but when their production exceeds their use,
they accumulate in the blood, causing ketosis, a condition that disturbs the body’s
normal acid-base balance, as Chapter 7 describes. (Highlight 9 explores ketosis
and the health consequences of low-carbohydrate diets further.)
To spare body protein and prevent ketosis, the body needs at least 50 to 100
grams of carbohydrate a day. Dietary recommendations urge people to select
abundantly from carbohydrate-rich foods to provide for considerably more.
Using Glucose to Make Fat After meeting its energy needs and filling its glyco-
gen stores to capacity, the body must find a way to handle any extra glucose. At first,
energy metabolism shifts to use more glucose instead of fat. If that isn’t enough to
restore glucose balance, the liver breaks glucose into smaller molecules and puts
them together into the more permanent energy-storage compound—fat. Thus when
carbohydrate is abundant, fat is either conserved or created. The fat then travels to
the fatty tissues of the body for storage. Unlike the liver cells, which can store only
enough glycogen to meet less than a day’s energy needs, fat cells can store seem-
ingly unlimited quantities of fat.
The Constancy of Blood Glucose
Every body cell depends on glucose for its fuel to some extent, and the cells of the
brain and the rest of the nervous system depend almost exclusively on glucose for
their energy. The activities of these cells never cease, and they have limited ability
to store glucose. Day and night, they continually draw on the supply of glucose in
the fluid surrounding them. To maintain the supply, a steady stream of blood
moves past these cells bringing more glucose from either the intestines (food) or
the liver (via glycogen breakdown or gluconeogenesis).
Maintaining Glucose Homeostasis To function optimally, the body must
maintain blood glucose within limits that permit the cells to nourish themselves. If
blood glucose falls below normal, ◆ a person may become dizzy and weak; if it rises
above normal, a person may become fatigued. Left untreated, fluctuations to the ex-
tremes—either high or low—can be fatal.
The Regulating Hormones Blood glucose homeostasis ◆ is regulated primarily
by two hormones: insulin, which moves glucose from the blood into the cells, and
glucagon, which brings glucose out of storage when necessary. Figure 4-12 (p. 114) de-
picts these hormonal regulators at work.
After a meal, as blood glucose rises, special cells of the pancreas respond by se-
creting insulin into the blood.* In general, the amount of insulin secreted corre-
sponds with the rise in glucose. As the circulating insulin contacts the receptors on
the body’s other cells, the receptors respond by ushering glucose from the blood into
the cells. Most of the cells take only the glucose they can use for energy right away,
but the liver and muscle cells can assemble the small glucose units into long,
branching chains of glycogen for storage. The liver cells can also convert glucose to
fat for export to other cells. Thus elevated blood glucose returns to normal levels as
excess glucose is stored as glycogen and fat.
When blood glucose falls (as occurs between meals), other special cells of the
pancreas respond by secreting glucagon into the blood.† Glucagon raises blood
glucose by signaling the liver to break down its glycogen stores and release glucose
into the blood for use by all the other body cells.
* The beta (BAY-tuh) cells, one of several types of cells in the pancreas, secrete insulin in response to ele-
vated blood glucose concentration.
† The alpha cells of the pancreas secrete glucagon in response to low blood glucose.
◆ Normal blood glucose (fasting): 70 to 100
mg/dL (published values vary slightly).
◆ Reminder: Homeostasis is the maintenance of
constant internal conditions by the body’s
control systems.
ketone (KEE-tone) bodies: the product of
the incomplete breakdown of fat when
glucose is not available in the cells.
ketosis (kee-TOE-sis): an undesirably high
concentration of ketone bodies in the blood
and urine.
acid-base balance: the equilibrium in the
body between acid and base concentrations
(see Chapter 12).
insulin (IN-suh-lin): a hormone secreted by
special cells in the pancreas in response to
(among other things) increased blood
glucose concentration. The primary role of
insulin is to control the transport of glucose
from the bloodstream into the muscle and
fat cells.
glucagon (GLOO-ka-gon): a hormone that is
secreted by special cells in the pancreas in
response to low blood glucose concentration
and elicits release of glucose from liver
glycogen stores.

114 • CHAPTER 4
Another hormone that signals the liver cells to release glucose is the “fight-or-
flight” hormone, epinephrine. When a person experiences stress, epinephrine
acts quickly, ensuring that all the body cells have energy fuel in emergencies.
Among its many roles in the body, epinephrine works to release glucose from liver
glycogen to the blood.
Balancing within the Normal Range The maintenance of normal blood glu-
cose ordinarily depends on two processes. When blood glucose falls below normal,
food can replenish it, or in the absence of food, glucagon can signal the liver to
break down glycogen stores. When blood glucose rises above normal, insulin can
signal the cells to take in glucose for energy. Eating balanced meals at regular inter-
vals helps the body maintain a happy medium between the extremes. Balanced
meals that provide abundant complex carbohydrates, including fibers and a little
fat, help to slow down the digestion and absorption of carbohydrate so that glucose
enters the blood gradually, providing a steady, ongoing supply.
Pancreas
Pancreas
Glucagon
Insulin
Liver
Fat cell
Intestine When a person eats,
blood glucose rises.
High blood glucose stimulates
the pancreas to release insulin.
As the body's cells use
glucose, blood levels decline.
Low blood glucose stimulates
the pancreas to release glucagon
into the bloodstream.
Glucagon stimulates liver cells
to break down glycogen and
release glucose into the blood.a
a
The stress hormone epinephrine and other
hormones also bring glucose out of storage.
Insulin stimulates the uptake of
glucose into cells and storage as
glycogen in the liver and muscles.
Insulin also stimulates the
conversion of excess glucose
into fat for storage.
Muscle
Liver
Blood glucose
begins to rise.
1
2
3
4
5
6
7
Glucose
Insulin
Glucagon
Glycogen
Key:
Blood vessel
FIGURE 4-12 Maintaining Blood Glucose Homeostasis
epinephrine (EP-ih-NEFF-rin): a hormone of
the adrenal gland that modulates the stress
response; formerly called adrenaline. When
administered by injection, epinephrine
counteracts anaphylactic shock by opening
the airways and maintaining heartbeat and
blood pressure.

Falling outside the Normal Range The influence of foods on blood glucose has
given rise to the oversimplification that foods govern blood glucose concentrations.
Foods do not; the body does. In some people, however, blood glucose regulation fails.
When this happens, either of two conditions can result: diabetes or hypoglycemia.
People with these conditions often plan their diets to help maintain their blood glu-
cose within a normal range.
Diabetes In diabetes, blood glucose surges after a meal and remains above nor-
mal levels ◆ because insulin is either inadequate or ineffective. Thus blood glucose is
central to diabetes, but dietary carbohydrates do not cause diabetes.
There are two main types of diabetes. In type 1 diabetes, the less common
type, the pancreas fails to produce insulin. Although the exact cause is unclear,
some research suggests that in genetically susceptible people, certain viruses ac-
tivate the immune system to attack and destroy cells in the pancreas as if they
were foreign cells. In type 2 diabetes, the more common type of diabetes, the
cells fail to respond to insulin. ◆ This condition tends to occur as a consequence
of obesity. As the incidence of obesity in the United States has risen in recent
decades, the incidence of diabetes has followed. This trend is most notable
among children and adolescents, as obesity among the nation’s youth reaches
epidemic proportions. Because obesity can precipitate type 2 diabetes, the best
preventive measure is to maintain a healthy body weight. Concentrated sweets
are not strictly excluded from the diabetic diet as they once were; they can be
eaten in limited amounts with meals as part of a healthy diet. Chapter 14 de-
scribes the type of diabetes that develops in some women during pregnancy (ges-
tational diabetes), and Chapter 26 gives full coverage to type 1 and type 2
diabetes and their associated problems.
Hypoglycemia In healthy people, blood glucose rises after eating and then grad-
ually falls back into the normal range. The transition occurs without notice. Should
blood glucose drop below normal, a person would experience the symptoms of hy-
poglycemia: weakness, rapid heartbeat, sweating, anxiety, hunger, and trem-
bling. Most commonly, hypoglycemia is a consequence of poorly managed diabetes.
Too much insulin, strenuous physical activity, inadequate food intake, or illness that
causes blood glucose levels to plummet.
Hypoglycemia in healthy people is rare. Most people who experience hypo-
glycemia need only adjust their diets by replacing refined carbohydrates with fiber-
rich carbohydrates and ensuring an adequate protein intake. In addition, smaller
meals eaten more frequently may help. Hypoglycemia caused by certain medica-
tions, pancreatic tumors, overuse of insulin, alcohol abuse, uncontrolled diabetes,
or other illnesses requires medical intervention.
The Glycemic Response The glycemic response refers to how quickly glucose
is absorbed after a person eats, how high blood glucose rises, and how quickly it
returns to normal. Slow absorption, a modest rise in blood glucose, and a smooth
return to normal are desirable (a low glycemic response). Fast absorption, a surge
in blood glucose, and an overreaction that plunges glucose below normal are less
desirable (a high glycemic response). Different foods have different effects on
blood glucose.
The rate of glucose absorption is particularly important to people with dia-
betes, who may benefit from limiting foods that produce too great a rise, or too
sudden a fall, in blood glucose. To aid their choices, they may be able to use the
glycemic index, a method of classifying foods according to their potential to
raise blood glucose. ◆ Figure 4-13 (p. 116) ranks selected foods by their glycemic
index. 8 Some studies have shown that selecting foods with a low glycemic index
is a practical way to improve glucose control. 9
Lowering the glycemic index of the diet may improve blood lipids and reduce the
risk of heart disease as well.10 A low glycemic diet may also help with weight man-
agement, although research findings are mixed.11 Fibers and other slowly digested
◆ Blood glucose (fasting):
• Prediabetes: 100 to 125 mg/dL
• Diabetes: 126 mg/dL
◆ The condition of having blood glucose levels
higher than normal, but below the diagnosis
of diabetes, is sometimes called prediabetes.
◆ A related term, glycemic load, reflects both
the glycemic index and the amount of
carbohydrate.
diabetes (DYE-uh-BEET-eez): a chronic
disorder of carbohydrate metabolism, usually
resulting from insufficient or ineffective
insulin.
type 1 diabetes: the less common type of
diabetes in which the pancreas fails to
produce insulin.
type 2 diabetes: the more common type of
diabetes in which the cells fail to respond to
insulin.
hypoglycemia (HIGH-po-gly-SEE-me-ah): an
abnormally low blood glucose
concentration.
glycemic (gly-SEEM-ic) response: the extent
to which a food raises the blood glucose
concentration and elicits an insulin response.
glycemic index: a method of classifying
foods according to their potential for raising
blood glucose.

116 • CHAPTER 4
carbohydrates prolong the presence of foods in the digestive tract, thus providing
greater satiety and diminishing the insulin response, which can help with weight
control.12 In contrast, the rapid absorption of glucose from a high glycemic diet
seems to increase the risk of heart disease and promote overeating in some over-
weight people.13
Despite these possible benefits, the usefulness of the glycemic index is sur-
rounded by controversy as researchers debate whether selecting foods based on the
glycemic index is practical or offers any real health benefits.14 Those opposing the
use of the glycemic index argue that it is not sufficiently supported by scientific re-
search.15 The glycemic index has been determined for relatively few foods, and
when the glycemic index has been established, it is based on an average of multi-
ple tests with wide variations in their results. Values vary because of differences in
the physical and chemical characteristics of foods, testing methods of laboratories,
and digestive processes of individuals.
Furthermore, the practical utility of the glycemic index is limited because this in-
formation is neither provided on food labels nor intuitively apparent. Indeed, a
food’s glycemic index is not always what one might expect. Ice cream, for exam-
ple, is a high-sugar food but produces less of a glycemic response than baked po-
tatoes, a high-starch food. This effect is most likely because the fat in the ice cream
slows GI motility and thus the rate of glucose absorption. Mashed potatoes pro-
duce more of a response than honey, probably because the fructose content of
honey has little effect on blood glucose. In fact, sugars such as fructose generally
have a moderate to low glycemic index.16 Perhaps most relevant to real life, a
food’s glycemic effect differs depending on plant variety, food processing, cooking
method, and whether it is eaten alone or with other foods.17 Most people eat a va-
riety of foods, cooked and raw, that provide different amounts of carbohydrate,
fat, and protein—all of which influence the glycemic index of a meal.
Paying attention to the glycemic index may not be necessary because current
guidelines already suggest many low glycemic index choices: whole grains,
legumes, vegetables, fruits, and milk products. In addition, eating frequent,
small meals spreads glucose absorption across the day and thus offers similar
metabolic advantages to eating foods with a low glycemic response. People
wanting to follow a low glycemic diet should be careful not to adopt a low-
carbohydrate diet as well. The problems associated with a low-carbohydrate diet
are addressed in Highlight 9.
Peanuts
Soybeans
Cashews,
cherries
Barley
Milk,
kidney
beans,
garbanzo
beans
Butter
beans
Yogurt
Tomato
juice,
navy
beans,
apples,
pears
Apple
juice
Bran
cereals,
black-eyed
peas,
peaches
Chocolate,
pudding
Grapes
Macaroni,
carrots,
green
peas,
baked
beans
Rye
bread,
orange
juice
Banana
Wheat
bread,
corn,
pound
cake
Brown
rice
Cola,
pineapple
Ice
cream
Raisins,
white
rice
Couscous
Watermelon,
popcorn,
bagel
Pumpkin,
doughnut
Sports
drinks,
jelly
beans
Cornflakes
Baked
potato
White
bread
HIGH
LOW
FIGURE 4-13 Glycemic Index of Selected Foods

Intakes of Sugars
Ever since people first discovered honey and dates, they have enjoyed the sweetness
of sugars. In the United States, the natural sugars of milk, fruits, vegetables, and
grains account for about half of the sugar intake; the other half consists of sugars
that have been refined and added to foods for a variety of purposes. ◆ The use of
added sugars has risen steadily over the past several decades, both in the United
States and around the world, with soft drinks and sugared fruit drinks accounting for
most of the increase.18 These added sugars assume various names on food labels: su-
crose, invert sugar, corn sugar, corn syrups and solids, high-fructose corn syrup, and
honey. A food is likely to be high in added sugars if its ingredient list starts
with any of the sugars named in the glossary (p. 118) or if it includes sev-
eral of them.
Health Effects of Sugars
In moderate amounts, sugars add pleasure to meals without harming
health. In excess, however, they can be detrimental in two ways. One, sug-
ars can contribute to nutrient deficiencies by supplying energy (kcalories)
without providing nutrients. Two, sugars contribute to tooth decay.
Nutrient Deficiencies Empty-kcalorie foods that contain lots of added
sugar such as cakes, candies, and sodas deliver glucose and energy with
few, if any, other nutrients. By comparison, foods such as whole grains, veg-
etables, legumes, and fruits that contain some natural sugars and lots of
starches and fibers deliver protein, vitamins, and minerals along with their
glucose and energy.
A person spending 200 kcalories of a day’s energy allowance on a 16-
ounce soda gets little of value for those kcaloric “dollars.” In contrast, a per-
son using 200 kcalories on three slices of whole-wheat bread gets 9 grams of
protein, 6 grams of fiber, plus several of the B vitamins with those kcalories.
For the person who wants something sweet, a reasonable compromise
might be two slices of bread with a teaspoon of jam on each. The amount of
sugar a person can afford to eat depends on how many kcalories are avail-
able beyond those needed to deliver indispensable vitamins and minerals.
With careful food selections, a typical adult can obtain all the needed nu-
trients within an allowance of about 1500 kcalories. Some people have more
generous energy allowances with which to “purchase” nutrients. For exam-
ple, an active teenage boy may need as many as 3000 kcalories a day. If he
eats mostly nutritious foods, then the “empty kcalories” of cola beverages
IN SUMMARY
Dietary carbohydrates provide glucose that can be used by the cells for energy,
stored by the liver and muscles as glycogen, or converted into fat if intakes ex-
ceed needs. All of the body’s cells depend on glucose; those of the central nerv-
ous system are especially dependent on it. Without glucose, the body is forced
to break down its protein tissues to make glucose and to alter energy metabo-
lism to make ketone bodies from fats. Blood glucose regulation depends pri-
marily on two pancreatic hormones: insulin to move glucose from the blood
into the cells when levels are high and glucagon to free glucose from glycogen
stores and release it into the blood when levels are low. The glycemic index
measures how blood glucose responds to foods.
Over half of the added sugars in our diet come from
soft drinks and table sugar, but baked goods, fruit
drinks, ice cream, candy, and breakfast cereals also
make substantial contributions.
added sugars: sugars and syrups used as an
ingredient in the processing and preparation
of foods such as breads, cakes, beverages,
jellies, and ice cream as well as sugars eaten
separately or added to foods at the table.
◆ As an additive, sugar:
• Enhances flavor
• Supplies texture and color to baked goods
• Provides fuel for fermentation, causing
bread to rise or producing alcohol
• Acts as a bulking agent in ice cream
and baked goods
• Acts as a preservative in jams
• Balances the acidity of tomato-
and vinegar-based products
©
Polara
Studios
Inc.

118 • CHAPTER 4
may be an acceptable addition to his diet. In contrast, an inactive older woman who
is limited to fewer than 1500 kcalories a day can afford to eat only the most nutrient-
dense foods.
Some people believe that because honey is a natural food, it is nutritious—or, at
least, more nutritious than sugar.* A look at their chemical structures reveals the
truth. Honey, like table sugar, contains glucose and fructose. The primary differ-
ence is that in table sugar the two monosaccharides are bonded together as a dis-
accharide, whereas in honey some of them are free. Whether a person eats
monosaccharides individually, as in honey, or linked together, as in table sugar,
they end up the same way in the body: as glucose and fructose.
Honey does contain a few vitamins and minerals, but not many, as Table 4-1
shows. Honey is denser than crystalline sugar, too, so it provides more energy per
spoonful.
brown sugar: refined white
sugar crystals to which
manufacturers have added
molasses syrup with natural
flavor and color; 91 to 96%
pure sucrose.
confectioners’ sugar: finely
powdered sucrose, 99.9% pure.
corn sweeteners: corn syrup and
sugars derived from corn.
corn syrup: a syrup made from
cornstarch that has been treated
with acid, high temperatures,
and enzymes that produce
glucose, maltose, and dextrins.
See also high-fructose corn syrup
(HFCS).
dextrose: an older name for
glucose.
granulated sugar: crystalline
sucrose; 99.9% pure.
high-fructose corn syrup (HFCS):
a syrup made from cornstarch
that has been treated with an
enzyme that converts some of
the glucose to the sweeter
fructose; made especially for
use in processed foods and
beverages, where it is the
predominant sweetener. With
a chemical structure similar to
sucrose, HFCS has a fructose
content of 42, 55, or 90%,
with glucose making up the
remainder.
honey: sugar (mostly sucrose)
formed from nectar gathered by
bees. An enzyme splits the
sucrose into glucose and
fructose. Composition and
flavor vary, but honey always
contains a mixture of sucrose,
fructose, and glucose.
invert sugar: a mixture of
glucose and fructose formed by
the hydrolysis of sucrose in a
chemical process; sold only in
liquid form and sweeter than
sucrose. Invert sugar is used as a
food additive to help preserve
freshness and prevent shrinkage.
levulose: an older name for
fructose.
maple sugar: a sugar (mostly
sucrose) purified from the
concentrated sap of the sugar
maple tree.
molasses: the thick brown syrup
produced during sugar refining.
Molasses retains residual sugar
and other by-products and a
few minerals; blackstrap
molasses contains significant
amounts of calcium and iron.
raw sugar: the first crop of
crystals harvested during sugar
processing. Raw sugar cannot
be sold in the United States
because it contains too much
filth (dirt, insect fragments, and
the like). Sugar sold as “raw
sugar” domestically has actually
gone through over half of the
refining steps.
turbinado (ter-bih-NOD-oh)
sugar: sugar produced using
the same refining process as
white sugar, but without the
bleaching and anti-caking
treatment. Traces of molasses
give turbinado its sandy color.
white sugar: pure sucrose or
“table sugar,” produced by
dissolving, concentrating, and
recrystallizing raw sugar.
GLOSSARY OF ADDED SUGARS
TABLE 4-1 Sample Nutrients in Sugar and Other Foods
The indicated portion of any of these foods provides approximately 100 kcalories. Notice that for a similar number of kcalories and grams of carbohydrate,
milk, legumes, fruits, grains, and vegetables offer more of the other nutrients than do the sugars.
Size of
100 kcal Carbohydrate Protein Calcium Iron Vitamin A Vitamin C
Portion (g) (g) (mg) (mg) (µg) (mg)
Foods
Milk, 1% low-fat 1 c 12 8 300 0.1 144 2
Kidney beans 1
⁄2 c 20 7 30 1.6 0 2
Apricots 6 24 2 30 1.1 554 22
Bread, whole-wheat 11
⁄2 slices 20 4 30 1.9 0 0
Broccoli, cooked 2 c 20 12 188 2.2 696 148
Sugars
Sugar, white 2 tbs 24 0 trace trace 0 0
Molasses, blackstrap 21
⁄2 tbs 28 0 343 12.6 0 0.1
Cola beverage 1 c 26 0 6 trace 0 0
Honey 11
⁄2 tbs 26 trace 2 0.2 0 trace
* Honey should never be fed to infants because of the risk of botulism. Chapters 16 and 19 provide
more details.

This is not to say that all sugar sources are alike, for some are more nutritious
than others. Consider a fruit, say, an orange. The fruit may give you the same
amounts of fructose and glucose and the same number of kcalories as a dose of
sugar or honey, but the packaging is more valuable nutritionally. The fruit’s sugars
arrive in the body diluted in a large volume of water, packaged in fiber, and mixed
with essential vitamins, minerals, and phytochemicals.
As these comparisons illustrate, the significant difference between sugar sources
is not between “natural” honey and “purified” sugar but between concentrated
sweets and the dilute, naturally occurring sugars that sweeten foods. You can sus-
pect an exaggerated nutrition claim when someone asserts that one product is
more nutritious than another because it contains honey.
Sugar can contribute to nutrient deficiencies only by displacing nutrients. For
nutrition’s sake, the appropriate attitude to take is not that sugar is “bad” and must
be avoided, but that nutritious foods must come first. If nutritious foods crowd
sugar out of the diet, that is fine—but not the other way around. As always, the
goals to seek are balance, variety, and moderation.
Dental Caries Sugars from foods and from the breakdown of starches in the
mouth can contribute to tooth decay. Bacteria in the mouth ferment the sugars and,
in the process, produce an acid that erodes tooth enamel (see Figure 4-14), causing
dental caries, or tooth decay. People can eat sugar without this happening,
though, for much depends on how long foods stay in the mouth. Sticky foods stay
on the teeth longer and continue to yield acid longer than foods that are readily
cleared from the mouth. For that reason, sugar in a juice consumed quickly, for ex-
ample, is less likely to cause dental caries than sugar in a pastry. By the same token,
the sugar in sticky foods such as dried fruits can be more detrimental than its quan-
tity alone would suggest.
Another concern is how often people eat sugar. Bacteria produce acid for 20 to
30 minutes after each exposure. If a person eats three pieces of candy at one time,
the teeth will be exposed to approximately 30 minutes of acid destruction. But, if
the person eats three pieces at half-hour intervals, the time of exposure increases to
90 minutes. Likewise, slowly sipping a sugary sports beverage may be more harm-
ful than drinking quickly and clearing the mouth of sugar. Nonsugary foods can
help remove sugar from tooth surfaces; hence, it is better to eat sugar with meals
than between meals.19 Foods such as milk and cheese may be particularly helpful
in minimizing the effects of the acids and in restoring the lost enamel.20
Beverages such as soft drinks, orange juice, and sports drinks not only contain
sugar but also have a low pH. These acidic drinks can erode tooth enamel and may
explain why dental erosion is highly prevalent today.21
The development of caries depends on several factors: the bacteria that reside in
dental plaque, the saliva that cleanses the mouth, the minerals that form the
teeth, and the foods that remain after swallowing. For most people, good oral hy-
giene will prevent ◆ dental caries. In fact, regular brushing (twice a day, with a flu-
oride toothpaste) and flossing may be more effective in preventing dental caries
than restricting sugary foods.
Nerve
Blood vessel
Gum
Crown
Root
canal
Bone
Dentin
Enamel
Pulp
(blood
vessels,
nerves)
Caries
FIGURE 4-14 Dental Caries
Dental caries begins when acid dissolves the
enamel that covers the tooth. If not repaired,
the decay may penetrate the dentin and
spread into the pulp of the tooth, causing
inflammation, abscess, and possible loss of
the tooth.
◆ To prevent dental caries:
• Limit between-meal snacks containing
sugars and starches.
• Brush and floss teeth regularly.
• If brushing and flossing are not possible,
at least rinse with water.
Reduce the incidence of dental caries by practicing good oral hygiene and
consuming sugar- and starch-containing foods and beverages less
frequently.
Controversies Surrounding Sugars
Sugars have been blamed for a variety of other health problems.22 The following
paragraphs evaluate some of these controversies.
dental caries: decay of teeth.
• caries = rottenness
dental plaque: a gummy mass of bacteria
that grows on teeth and can lead to dental
caries and gum disease.

120 • CHAPTER 4
Controversy: Does Sugar Cause Obesity? Over the past three decades, obe-
sity rates have risen sharply in the United States. During the same period, consump-
tion of added sugars has reached an all-time high—much of it because of the
dramatic rise in high-fructose corn syrup used in beverages. Between 1977 and
2001, as people grew fatter, their intake of kcalories from fruit drinks and punches
doubled and kcalories from soft drinks nearly tripled.23 Although the use of this
sweetener parallels unprecedented gains of body fatness, does it mean that the in-
creasing sugar intakes are responsible for the increase in obesity? 24
When eaten in excess of need, energy from added sugars contributes to body fat
stores, just as excess energy from other sources does. Added sugars provide excess
kcalories, raising the risk of weight gain and type 2 diabetes.25 When total kcalorie
intakes are controlled, however, moderate amounts of sugar do not cause obesity.26
People with diets high in added sugars often consume more kcalories each day
than people with lower sugar intakes. Adolescents, for example, who drink as
much as 26 ounces or more (about two cans) of sugar-sweetened soft drinks daily,
consume 400 more kcalories a day than teens who don’t. Overweight children and
adolescents increase their risk of becoming obese by 60 percent with each addi-
tional syrup-sweetened drink they add to their daily diet. The liquid form of sugar
in soft drinks makes it especially easy to overconsume kcalories.27 Investigators are
evaluating these and other possible links between fructose in the syrupy sweeteners
of soft drinks and weight gain.28 Research suggests that fructose from these added
sugars favors the fat-making pathways.29
Limiting selections of foods and beverages high in added sugars can be an effec-
tive weight-loss strategy, especially for people whose excess kcalories come pri-
marily from added sugars.30 Replacing a can of cola with a glass of water every
day, for example, can help a person lose a pound (or at least not gain a pound) in
one month. That may not sound like much, but it adds up to more than 10 pounds
a year, for very little effort.
Controversy: Does Sugar Cause Heart Disease? A diet high in added sugars
can alter blood lipids to favor heart disease.31 (Lipids include fats and cholesterol, as
Chapter 5 explains.) This effect is most dramatic in people who respond to sucrose
with abnormally high insulin secretions, which promote the making of excess fat.32
For most people, though, moderate sugar intakes do not elevate blood lipids. To keep
these findings in perspective, consider that heart disease correlates most closely with
factors that have nothing to do with nutrition, such as smoking and genetics.
Among dietary risk factors, several—such as saturated fats, trans fats, and choles-
terol—have much stronger associations with heart disease than do sugar intakes.
Controversy: Does Sugar Cause Misbehavior in Children and Criminal Be-
havior in Adults? Sugar has been blamed for the misbehaviors of hyperactive
children, delinquent adolescents, and lawbreaking adults. Such speculations have
been based on personal stories and have not been confirmed by scientific research.
No scientific evidence supports a relationship between sugar and hyperactivity or
other misbehaviors. Chapter 15 provides accurate information on diet and chil-
dren’s behavior.
Controversy: Does Sugar Cause Cravings and Addictions? Foods in gen-
eral, and carbohydrates and sugars more specifically, are not physically addictive in
the ways that drugs are. Yet some people describe themselves as having “carbohy-
drate cravings” or being “sugar addicts.” One frequently noted theory is that people
seek carbohydrates as a way to increase their levels of the brain neurotransmitter
serotonin, which elevates mood. Interestingly, when those with self-described car-
bohydrate cravings indulge, they tend to eat more of everything, but the percentage
of energy from carbohydrates remains unchanged.33 Alcohol also raises serotonin
levels, and alcohol-dependent people who crave carbohydrates seem to handle so-
briety better when given a high-carbohydrate diet.
One reasonable explanation for the carbohydrate cravings that some people ex-
perience involves the self-imposed labeling of a food as both “good” and “bad”—that
is, one that is desirable but should be eaten with restraint. Chocolate is a familiar ex-
You receive about the same amount and kinds
of sugars from an orange as from a tablespoon
of honey, but the packaging makes a big
nutrition difference.
serotonin (SER-oh-TONE-in): a
neurotransmitter important in sleep
regulation, appetite control, intestinal
motility, obsessive-compulsive behaviors,
and mood disorders.
Matthew
Farruggio

ample. Restricting intake heightens the desire further (a “craving”). Then “addiction”
is used to explain why resisting the food is so difficult and, sometimes, even impossi-
ble. But the “addiction” is not pharmacological; a capsule of the psychoactive sub-
stances commonly found in chocolate, for example, does not satisfy the craving.
Recommended Intakes of Sugars
Because added sugars deliver kcalories but few or no nutrients, the 2005 Dietary
Guidelines urge consumers to “choose and prepare foods and beverages with little
added sugars.” The USDA Food Guide counts these sugar kcalories (and those from
solid fats and alcohol) as discretionary kcalories. Most people need to limit their use
of added sugars. ◆ Estimates indicate that, on average, each person in the United
States consumes about 105 pounds (almost 50 kilograms) of added sugar per year,
or about 30 teaspoons (about 120 grams) of added sugar a day, an amount that ex-
ceeds these guidelines.34
Choose and prepare foods and beverages with little added sugars.
Estimating the added sugars in a diet is not always easy for consumers. Food la-
bels list the total grams of sugar a food provides, but this total reflects both added
sugars and those occurring naturally in foods. To help estimate sugar and energy
intakes accurately, the list in the margin ◆ shows the amounts of concentrated
sweets that are equivalent to 1 teaspoon of white sugar. These sugars all provide
about 5 grams of carbohydrate and about 20 kcalories per teaspoon. Some are
lower (16 kcalories for table sugar), and others are higher (22 kcalories for honey),
but a 20-kcalorie average is an acceptable approximation. For a person who uses
catsup liberally, it may help to remember that 1 tablespoon of catsup supplies
about 1 teaspoon of sugar.
The DRI Committee did not set an upper level for sugar, but as mentioned, ex-
cessive intakes can interfere with sound nutrition and dental health. Few people
can eat lots of sugary treats and still meet all of their nutrient needs without ex-
ceeding their kcalorie allowance. Specifically, the DRI suggests that added sugars
should account for no more than 25 percent of the day’s total energy intake.35
When added sugars occupy this much of a diet, however, intakes from the five food
groups fall below recommendations. For a person consuming 2000 kcalories a day,
25 percent represents 500 kcalories (that is, 125 grams, or 31 teaspoons) from con-
centrated sugars—and that’s a lot of sugar. ◆ Perhaps an athlete in training whose
energy needs are high can afford the added sugars from sports drinks without com-
promising nutrient intake, but most people do better by limiting their use of added
sugars. The World Health Organization (WHO) and the Food and Agriculture
Organization (FAO) suggest restricting consumption of added sugars to less than
10 percent of total energy.
◆ USDA Food Guide amounts of added sugars
that can be included as discretionary kcalo-
ries when food choices are nutrient dense
and fat 30% total kcal:
• 3 tsp for 1600 kcal diet
◆ 1 tsp white sugar
• 1 tsp brown sugar
• 1 tsp candy
• 1 tsp corn sweetener or corn syrup
• 1 tsp honey
• 1 tsp jam or jelly
• 1 tsp maple sugar or maple syrup
• 1 tsp molasses
• 11/2 oz carbonated soda
• 1 tbs catsup
◆ For perspective, each of these concentrated
sugars provides about 500 kcal:
• 40 oz cola
• 1/2 c honey
• 125 jelly beans
• 23 marshmallows
• 30 tsp sugar
How many kcalories from sugar does your
favorite beverage or snack provide?
IN SUMMARY
Sugars pose no major health threat except for an increased risk of dental
caries. Excessive intakes, however, may displace needed nutrients and fiber
and may contribute to obesity when energy intake exceeds needs. A person de-
ciding to limit daily sugar intake should recognize that not all sugars need to
be restricted, just concentrated sweets, which are relatively empty of other nu-
trients and high in kcalories. Sugars that occur naturally in fruits, vegetables,
and milk are acceptable.

122 • CHAPTER 4
Intakes of Starch and Fibers
Carbohydrates and fats are the two major sources of energy in the diet. When one is
high, the other is usually low—and vice versa. A diet that provides abundant carbo-
hydrate (45 to 65 percent of energy intake) and some fat (20 to 35 percent of energy
intake) within a reasonable energy allowance best supports good health. To increase
carbohydrate in the diet, focus on whole grains, vegetables, legumes, and fruits—
foods noted for their starch, fibers, and naturally occurring sugars.
Health Effects of Starch and Fibers
In addition to starch, fibers, and natural sugars, whole grains, vegetables, legumes,
and fruits supply valuable vitamins and minerals and little or no fat. The following
paragraphs describe some of the health benefits of diets that include a variety of
these foods daily.
Heart Disease High-carbohydrate diets, especially those rich in whole grains,
may protect against heart disease and stroke, although sorting out the exact reasons
why can be difficult.36 Such diets are low in animal fat and cholesterol and high in
fibers, vegetable proteins, and phytochemicals—all factors associated with a lower
risk of heart disease. (The role of animal fat and cholesterol in heart disease is dis-
cussed in Chapter 5. The role of vegetable proteins in heart disease is presented in
Chapter 6. The benefits of phytochemicals in disease prevention are featured in
Highlight 13.)
Foods rich in soluble fibers (such as oat bran, barley, and legumes) lower blood
cholesterol ◆ by binding with bile acids and thereby increasing their excretion.
Consequently, the liver must use its cholesterol to make new bile acids. In addition,
the bacterial by-products of fiber fermentation in the colon also inhibit cholesterol
synthesis in the liver. The net result is lower blood cholesterol.37
Several researchers have speculated that fiber may also exert its effect by dis-
placing fats in the diet. Whereas this is certainly helpful, even when dietary fat is
low, high intakes of fibers exert a separate and significant cholesterol-lowering ef-
fect. In other words, a high-fiber diet helps to decrease the risk of heart disease inde-
pendent of fat intake.38
Diabetes High-fiber foods—especially whole grains—play a key role in reducing
the risk of type 2 diabetes.39 When soluble fibers trap nutrients and delay their
transit through the GI tract, glucose absorption is slowed, which helps to prevent
the glucose surge and rebound that seem to be associated with diabetes onset.
GI Health Dietary fibers enhance the health of the large intestine. The healthier
the intestinal walls, the better they can block absorption of unwanted constituents.
Fibers such as cellulose (as in cereal brans, fruits, and vegetables) increase stool
weight, easing passage, and reduce transit time. In this way, the fibers help to alle-
viate or prevent constipation.
Taken with ample fluids, fibers help to prevent several GI disorders. Large, soft
stools ease elimination for the rectal muscles and reduce the pressure in the lower
bowel, making it less likely that rectal veins will swell (hemorrhoids). Fiber prevents
compaction of the intestinal contents, which could obstruct the appendix and per-
mit bacteria to invade and infect it (appendicitis). In addition, fiber stimulates the
GI tract muscles so that they retain their strength and resist bulging out into pouches
known as diverticula (illustrated in Figure H3-3 on p. 95).40
Cancer Many, but not all, research studies suggest that increasing dietary fiber
protects against colon cancer.41 When the largest study of diet and cancer to date
examined the diets of over a half million people in ten countries for four and a half
Foods rich in starch and fiber offer many
health benefits.
◆ Consuming 5 to 10 g of soluble fiber daily re-
duces blood cholesterol by 3 to 5%. For per-
spective, 1/2 c dry oat bran provides 8 g of
fiber, and 1 c cooked barley or 1/2 c cooked
legumes provides about 6 g of fiber.
©
Rita
Mass/The
Image
Bank/Getty
Images

years, the researchers found an inverse association between dietary fiber and colon
cancer.42 People who ate the most dietary fiber (35 grams per day) reduced their
risk of colon cancer by 40 percent compared with those who ate the least fiber (15
grams per day). Importantly, the study focused on dietary fiber, not fiber supple-
ments or additives, which lack valuable nutrients and phytochemicals that also
help protect against cancer. Plant foods—vegetables, fruits, and whole-grain prod-
ucts—reduce the risks of colon and rectal cancers.43
Fibers may help prevent colon cancer by diluting, binding, and rapidly remov-
ing potential cancer-causing agents from the colon. In addition, soluble fibers stim-
ulate bacterial fermentation of resistant starch and fiber in the colon, a process that
produces short-chain fatty acids that lower the pH. These small fat molecules acti-
vate cancer-killing enzymes and inhibit inflammation in the colon.44
Weight Management High-fiber and whole-grain foods help a person to main-
tain a healthy body weight.45 Foods rich in complex carbohydrates tend to be low
in fat and added sugars and can therefore promote weight loss by delivering less
energy ◆ per bite. In addition, as fibers absorb water from the digestive juices, they
swell, creating feelings of fullness and delaying hunger.
Many weight-loss products on the market today contain bulk-inducing fibers
such as methylcellulose, but buying pure fiber compounds like this is neither nec-
essary nor advisable. Most experts agree that the health and weight management
benefits attributed to fiber may come from other constituents of fiber-containing
foods, and not from fiber alone.46 For this reason, consumers should select whole
grains, legumes, fruits, and vegetables instead of fiber supplements. High-fiber
foods not only add bulk to the diet but are economical and nutritious as well. Table
4-2 summarizes fibers and their health benefits.
Harmful Effects of Excessive Fiber Intake Despite fibers’ benefits to health, a
diet high in fiber also has a few drawbacks. A person who has a small capacity and
eats mostly high-fiber foods may not be able to take in enough food to meet energy
or nutrient needs. The malnourished, the elderly, and young children adhering to
all-plant (vegan) diets are especially vulnerable to this problem.
Launching suddenly into a high-fiber diet can cause temporary bouts of abdom-
inal discomfort, gas, and diarrhea and, more seriously, can obstruct the GI tract. To
◆ Reminder:
• Carbohydrate: 4 kcal/g
• Fat: 9 kcal/g
TABLE 4-2 Dietary Fibers: Their Characteristics, Food Sources, and Health Effects in the Body
Fiber Characteristics Major Food Sources Actions in the Body Health Benefits
Soluble, viscous, more
fermentable
• Gums and mucilages
• Pectins
• Psylliuma
• Some hemicelluloses
Insoluble, nonviscous,
less fermentable
• Cellulose
• Lignins
• Psylliuma
• Resistant starch
• Many hemicelluloses
Whole-grain products (barley, oats,
oat bran, rye), fruits (apples, citrus),
legumes, seeds and husks, vegeta-
bles; also extracted and used as
food additives
Brown rice, fruits, legumes, seeds,
vegetables (cabbage, carrots,
brussels sprouts), wheat bran,
whole grains; also extracted and
used as food additives
• Lower blood cholesterol by
binding bile
• Slow glucose absorption
• Slow transit of food through
upper GI tract
• Hold moisture in stools, soften-
ing them
• Yield small fat molecules after
fermentation that the colon can
use for energy
• Increase fecal weight and speed
fecal passage through colon
• Provide bulk and feelings of
fullness
• Lower risk of heart disease
• Lower risk of diabetes
• Alleviate constipation
• Lower risks of diverticulosis,
hemorrhoids, and appendicitis
• May help with weight
management
aPsyllium, a fiber laxative and cereal additive, has both soluble and insoluble properties.

124 • CHAPTER 4
prevent such complications, a person adopting a high-fiber diet can take the fol-
lowing precautions:
• Increase fiber intake gradually over several weeks to give the GI tract time to
adapt.
• Drink plenty of liquids to soften the fiber as it moves through the GI tract.
• Select fiber-rich foods from a variety of sources—fruits, vegetables, legumes,
and whole-grain breads and cereals.
Some fibers can limit the absorption of nutrients by speeding the transit of foods
through the GI tract and by binding to minerals. When mineral intake is adequate,
however, a reasonable intake of high-fiber foods does not seem to compromise
mineral balance.
Clearly, fiber is like all the nutrients in that “more” is “better” only up to a point.
Again, the key words are balance, moderation, and variety.
IN SUMMARY
Adequate intake of fiber:
• Fosters weight management
• Lowers blood cholesterol
• May help prevent colon cancer
• Helps prevent and control diabetes
• Helps prevent and alleviate hemorrhoids
• Helps prevent appendicitis
• Helps prevent diverticulosis
Excessive intake of fiber:
• Displaces energy- and nutrient-dense foods
• Causes intestinal discomfort and distention
• May interfere with mineral absorption
Recommended Intakes of Starch and Fibers
Dietary recommendations suggest that carbohydrates provide about half (45 to 65
percent) of the energy requirement. A person consuming 2000 kcalories a day
should therefore have 900 to 1300 kcalories of carbohydrate, or about 225 to 325
grams. ◆ This amount is more than adequate to meet the RDA ◆ for carbohydrate,
which is set at 130 grams per day, based on the average minimum amount of glu-
cose used by the brain.47
When it established the Daily Values that appear on food labels, the Food and
Drug Administration (FDA) used a 60 percent of kcalories guideline in setting the
Daily Value ◆ for carbohydrate at 300 grams per day. For most people, this means
increasing total carbohydrate intake. To this end, the Dietary Guidelines encourage
people to choose a variety of whole grains, vegetables, fruits, and legumes daily.
◆ The Aids to Calculations section at the end
of this book explains how to solve such
problems.
◆ RDA for carbohydrate:
• 130 g/day
• 45 to 65% of energy intake
◆ Daily Value:
• 300 g carbohydrate (based on 60% of
2000 kcal diet)
◆ To increase your fiber intake:
• Eat whole-grain cereals that contain 5
g fiber per serving for breakfast.
• Eat raw vegetables.
• Eat fruits (such as pears) and vegetables
(such as potatoes) with their skins.
• Add legumes to soups, salads, and
casseroles.
• Eat fresh and dried fruit for snacks.
◆ Daily Value:
• 25 g fiber (based on 11.5 g/1000 kcal)
Choose fiber-rich fruits, vegetables, and whole grains often.
Recommendations for fiber ◆ suggest the same foods just mentioned: whole
grains, vegetables, fruits, and legumes, which also provide minerals and vitamins.
The FDA set the Daily Value ◆ for fiber at 25 grams, rounding up from the recom-

mended 11.5 grams per 1000-kcalories for a 2000-kcalorie intake. The DRI recom-
mendation is slightly higher, at 14 grams per 1000-kcalorie intake. Similarly, the
American Dietetic Association suggests 20 to 35 grams of dietary fiber daily, which
is about two times higher than the average intake in the United States.48 An effec-
tive way to add fiber while lowering fat is to substitute plant sources of proteins
(legumes) for animal sources (meats). Table 4-3 presents a list of fiber sources.
As mentioned earlier, too much fiber is no better than too little. The World
Health Organization recommends an upper limit of 40 grams of dietary fiber a
day.
A diet following the USDA Food Guide, which includes several servings of fruits, veg-
etables, and grains daily, can easily supply the recommended amount of carbohy-
drates and fiber. In selecting high-fiber foods, keep in mind the principle of variety.
The fibers in oats lower cholesterol, whereas those in bran help promote GI tract
health. (Review Table 4-2 to see the diverse health effects of various fibers.)
Grains An ounce-equivalent of most foods in the grain group provides about 15
grams of carbohydrate, mostly as starch. Be aware that some foods in this group,
especially snack crackers and baked goods such as biscuits, croissants, and
muffins, contain added sugars, added fat, or both. When selecting from the grain
group, be sure to include at least half as whole-grain products (see Figure 4-15,
p. 126). The “3 are Key” message may help consumers to remember to choose a
whole-grain cereal for breakfast, a whole-grain bread for lunch, and a whole-
grain pasta or rice for dinner.
TABLE 4-3 Fiber in Selected Foods
Grains
Whole-grain products provide about 1 to 2 grams (or more) of fiber per serving:
• 1 slice whole-wheat, pumpernickel, rye bread
• 1 oz ready-to-eat cereal (100% bran cereals contain 10 grams or more)
• 1
⁄2 c cooked barley, bulgur, grits, oatmeal
Vegetable
Most vegetables contain about 2 to 3 grams of fiber per serving:
• 1 c raw bean sprouts
• 1
⁄2 c cooked broccoli, brussels sprouts, cabbage, carrots, cauliflower, collards, corn, eggplant,
green beans, green peas, kale, mushrooms, okra, parsnips, potatoes, pumpkin, spinach, sweet
potatoes, swiss chard, winter squash
• 1
⁄2 c chopped raw carrots, peppers
Fruit
Fresh, frozen, and dried fruits have about 2 grams of fiber per serving:
• 1 medium apple, banana, kiwi, nectarine, orange, pear
• 1
⁄2 c applesauce, blackberries, blueberries, raspberries, strawberries
• Fruit juices contain very little fiber
Legumes
Many legumes provide about 6 to 8 grams of fiber per serving:
• 1
⁄2 c cooked baked beans, black beans, black-eyed peas, kidney beans, navy beans, pinto beans
Some legumes provide about 5 grams of fiber per serving:
• 1
⁄2 c cooked garbanzo beans, great northern beans, lentils, lima beans, split peas
NOTE: Appendix H provides fiber grams for over 2000 foods.
©
Polara
Studios,
Inc.
©
Polara
Studios,
Inc.
©
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Studios,
Inc.
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Blue/
Getty
Images

126 • CHAPTER 4
Vegetables The amount of carbohydrate a serving of vegetables provides depends
primarily on its starch content. Starchy vegetables—a half-cup of cooked corn, peas,
or potatoes—provide about 15 grams of carbohydrate per serving. A serving of most
other nonstarchy vegetables—such as a half-cup of broccoli, green beans, or toma-
toes—provides about 5 grams.
Fruits A typical fruit serving—a small banana, apple, or orange or a half-cup of
most canned or fresh fruit—contains an average of about 15 grams of carbohydrate,
mostly as sugars, including the fruit sugar fructose. Fruits vary greatly in their water
and fiber contents and, therefore, in their sugar concentrations.
Milks and Milk Products A serving (a cup) of milk or yogurt provides about 12
grams of carbohydrate. Cottage cheese provides about 6 grams of carbohydrate per
cup, but most other cheeses contain little, if any, carbohydrate.
Meats and Meat Alternates With two exceptions, foods in the meats and meat
alternates group deliver almost no carbohydrate to the diet. The exceptions are nuts,
which provide a little starch and fiber along with their abundant fat, and legumes,
which provide an abundance of both starch and fiber. Just a half-cup serving of
legumes provides about 20 grams of carbohydrate, a third from fiber.
Read Food Labels Food labels list the amount, in grams, of total carbohydrate—
including starch, fibers, and sugars—per serving (review Figure 4-15). Fiber grams
are also listed separately, as are the grams of sugars. (With this information, you can
Total Fat 1.5g 2%
Serving size 1 slice (30g)
Servings Per Container 15
Calories 90
Amount per serving
Calories from Fat 14
% Daily Value*
Sodium 135mg 6%
5%
Protein 4g
8%
Sugars 2g
Dietary fiber 2g
Total Carbohydrate 15g
Nutrition Facts
MADE FROM: UNBROMATED STONE
GROUND 100% WHOLE WHEAT FLOUR,
WATER, CRUSHED WHEAT, HIGH FRUCTOSE
CORN SYRUP, PARTIALLY HYDROGENATED
VEGETABLE SHORTENING (SOYBEAN AND
COTTONSEED OILS), RAISIN JUICE
CONCENTRATE, WHEAT GLUTEN, YEAST,
WHOLE WHEAT FLAKES, UNSULPHURED
MOLASSES, SALT, HONEY, VINEGAR,
ENZYME MODIFIED SOY LECITHIN,
CULTURED WHEY, UNBLEACHED WHEAT
FLOUR AND SOY LECITHIN.
Total Fat 1.5g 2%
Serving size 1 slice (30g)
Servings Per Container 15
Calories 90
Amount per serving
Calories from Fat 14
% Daily Value*
Sodium 220mg 9%
5%
Protein 4g
Sugars 2g
15g
Nutrition Facts
INGREDIENTS: UNBLEACHED ENRICHED
WHEAT FLOUR [MALTED BARLEY FLOUR,
NIACIN, REDUCED IRON, THIAMIN
MONONITRATE (VITAMIN B1), RIBOFLAVIN
(VITAMIN B2), FOLIC ACID], WATER, HIGH
FRUCTOSE CORN SYRUP, MOLASSES,
PARTIALLY HYDROGENATED SOYBEAN
OIL, YEAST, CORN FLOUR, SALT,
GROUND CARAWAY, WHEAT GLUTEN,
CALCIUM PROPIONATE (PRESERVATIVE),
MONOGLYCERIDES, SOY LECITHIN.
Total Carbohydrate
Dietary fiber less than 1g 2%
FIGURE 4-15 Bread Labels Compared
Food labels list the quantities of total carbohydrate, dietary fiber, and sugars.
Total carbohydrate and dietary fiber are also stated as “% Daily Values.” A close
look at these two labels reveals that bread made from whole wheat-flour provides
almost three times as much fiber as the one made mostly from refined wheat
flour. When the words whole wheat or whole grain appear on the label, the bread
inside contains all of the nutrients that bread can provide.

calculate starch grams ◆ by subtracting the grams of fibers and sugars from the to-
tal carbohydrate.) Sugars reflect both added sugars and those that occur naturally
in foods. Total carbohydrate and dietary fiber are also expressed as “% Daily Values”
for a person consuming 2000 kcalories; there is no Daily Value for sugars.
IN SUMMARY
Clearly, a diet rich in complex carbohydrates—starches and fibers—supports
efforts to control body weight and prevent heart disease, cancer, diabetes, and
GI disorders. For these reasons, recommendations urge people to eat plenty of
whole grains, vegetables, legumes, and fruits—enough to provide 45 to 65 per-
cent of the daily energy intake from carbohydrate.
Foods that derive from plants—whole grains, vegetables, legumes, and fruits—natu-
rally provide ample carbohydrates and fiber with little or no fat. Refined foods often
contain added sugars and fat.
■ List the types and amounts of grain products you eat daily, making note of
which are whole-grain or refined foods and how your choices could include
more whole-grain options.
■ List the types and amounts of fruits and vegetables you eat daily, making note
of how many are dark-green, orange, or deep yellow, how many are starchy or
legumes, and how your choices could include more of these options.
■ Describe choices you can make in selecting and preparing foods and beverages
to lower your intake of added sugars.
• Search for “lactose intolerance” at the U.S. Government
• Search for “sugars” and “fiber” at the International Food
Information Council site: www.ific.org
• Learn more about dental caries from the American Dental
Association and the National Institute of Dental and
Craniofacial Research: www.ada.org and
www.nidcr.nih.gov
• Learn more about diabetes from the American Diabetes
Association, the Canadian Diabetes Association, and the
National Institute of Diabetes and Digestive and Kidney
Diseases: www.diabetes.org, www.diabetes.ca, and
www.niddk.nih.gov
◆ To calculate starch grams using the first la-
bel in Figure 4-15:
15 g total 4 g (dietary fiber sugars)
11 g starch
In today’s world, there is one other reason why plant foods rich in complex carbohy-
drates and natural sugars are a better choice than animal foods or foods high in
concentrated sweets. In general, less energy and fewer resources are required to grow
and process plant foods than to produce sugar or foods derived from animals.

128 • CHAPTER 4
nutrition-related calculations. Although the situations are
hypothetical, the numbers are real, and calculating the answers
(check them on p. 131) provides a valuable lesson. Be sure to
show your calculations for each problem.
Health recommendations suggest that 45 to 65 percent of
the daily energy intake come from carbohydrates. Stating
recommendations in terms of percentage of energy intake is
meaningful only if energy intake is known. The following
exercises illustrate this concept.
1. Calculate the carbohydrate intake (in grams) for a stu-
dent who has a high carbohydrate intake (70 percent of
energy intake) and a moderate energy intake (2000
kcalories a day).
How does this carbohydrate intake compare to the
Daily Value of 300 grams? To the 45 to 65 percent
recommendation?
2. Now consider a professor who eats half as much carbohy-
drate as the student (in grams) and has the same energy
intake. What percentage does carbohydrate contribute to
the daily intake?
How does carbohydrate intake compare to the
recommendation?
3. Now consider an athlete who eats twice as much carbohy-
drate (in grams) as the student and has a much higher
energy intake (6000 kcalories a day). What percentage
does carbohydrate contribute to this person’s daily intake?
How does carbohydrate intake compare to the
recommendation?
4. One more example. In an attempt to lose weight, a per-
son adopts a diet that provides 150 grams of carbohy-
drate per day and limits energy intake to 1000 kcalories.
What percentage does carbohydrate contribute to this
person’s daily intake?
How does this carbohydrate intake compare to the
recommendation?
These exercises should convince you of the importance of ex-
amining actual intake as well the percentage of energy intake.
Log on to academic.cenage.com/login.
1. Which carbohydrates are described as simple and which
are complex? (p. 101)
2. Describe the structure of a monosaccharide and name
the three monosaccharides important in nutrition.
Name the three disaccharides commonly found in foods
and their component monosaccharides. In what foods
are these sugars found? (pp. 102–105)
3. What happens in a condensation reaction? In a hydroly-
sis reaction? (p. 104)
4. Describe the structure of polysaccharides and name the
ones important in nutrition. How are starch and glyco-
gen similar, and how do they differ? How do the fibers
differ from the other polysaccharides? (pp. 105–107)
5. Describe carbohydrate digestion and absorption. What
role does fiber play in the process? (pp. 107–110)
6. What are the possible fates of glucose in the body? What is
the protein-sparing action of carbohydrate? (pp. 111–113)
7. How does the body maintain its blood glucose concen-
tration? What happens when the blood glucose concen-
tration rises too high or falls too low? (pp. 113–117)
8. What are the health effects of sugars? What are the di-
etary recommendations regarding concentrated sugar
intakes? (pp. 117–121)
9. What are the health effects of starches and fibers? What
are the dietary recommendations regarding these com-
plex carbohydrates? (pp. 122–125)
10. What foods provide starches and fibers? (pp. 125–126)
1. Carbohydrates are found in virtually all foods except:
a. milks.
b. meats.
c. breads.
d. fruits.
2. Disaccharides include:
a. starch, glycogen, and fiber.
b. amylose, pectin, and dextrose.
c. sucrose, maltose, and lactose.
d. glucose, galactose, and fructose.
3. The making of a disaccharide from two monosaccharides
is an example of:
a. digestion.
b. hydrolysis.
c. condensation.
d. gluconeogenesis.
STUDY QUESTIONS

4. The storage form of glucose in the body is:
a. insulin.
b. maltose.
c. glucagon.
d. glycogen.
5. The significant difference between starch and cellulose
is that:
a. starch is a polysaccharide, but cellulose is not.
b. animals can store glucose as starch, but not as
cellulose.
c. hormones can make glucose from cellulose, but
not from starch.
d. digestive enzymes can break the bonds in starch,
but not in cellulose.
6. The ultimate goal of carbohydrate digestion and absorp-
tion is to yield:
a. fibers.
b. glucose.
c. enzymes.
d. amylase.
7. The enzyme that breaks a disaccharide into glucose and
galactose is:
a. amylase.
b. maltase.
c. sucrase.
d. lactase.
8. With insufficient glucose in metabolism, fat fragments
combine to form:
a. dextrins.
b. mucilages.
c. phytic acids.
d. ketone bodies.
9. What does the pancreas secrete when blood glucose
rises? When blood glucose falls?
a. insulin; glucagon
b. glucagon; insulin
c. insulin; glycogen
d. glycogen; epinephrine
10. What percentage of the daily energy intake should come
from carbohydrates?
a. 15 to 20
b. 25 to 30
c. 45 to 50
d. 45 to 65
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cardiovascular disease in the Framingham
Offspring Study, American Journal of Clinical
Nutrition 76 (2002): 390–398; S. Liu, Intake
of refined carbohydrates and whole grain
foods in relation to risk of type 2 diabetes
mellitus and coronary heart disease, Journal
of the American College of Nutrition 21
(2002): 298–306.
37. K. M. Behall, D. J. Scholfield, and J. Hall-
frisch, Diets containing barley significantly
reduce lipids in mildly hypercholesterolemic
men and women, American Journal of Clinical
Nutrition 80 (2004): 1185–1193; B. M. Davy
and coauthors, High-fiber oat cereal com-
pared with wheat cereal consumption favor-
ably alters LDL-cholesterol subclass and
particle numbers in middle-aged and older
men, American Journal of Clinical Nutrition 76
(2002): 351–358; D. J. A. Jenkins and coau-
thors, Soluble fiber intake at a dose approved
by the US Food and Drug Administration for
a claim of health benefits: Serum lipid risk
factors for cardiovascular disease assessed in
a randomized controlled crossover trial,
(2002): 834–839.
38. U. A. Ajani, E. S. Ford, and A. H. Mokdad,
Dietary fiber and C-reactive protein: Find-
ings from National Health and Nutrition
Examination Survey Data, Journal of Nutri-
tion 134 (2004): 1181–1185.
39. M. K. Jenson and coauthors, Whole grains,
bran and germ in relation to homocysteine
and markers of glycemic control, lipids,
and inflammation, American Journal of
Clinical Nutrition 83 (2006): 275–283; T. T.
Fung and coauthors, Whole-grain intake
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venting diverticular disease: Review of recent
evidence on high-fibre diets, Canadian
Family Physician 48 (2002): 1632–1637.
41. Y. Park and coauthors, Dietary fiber intake
and risk of colorectal cancer, Journal of the
American Medical Association 294 (2005):
2849–2857; T. Asano and R. S. McLeod,
Dietary fibre for the prevention of colorec-
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An observational study, Lancet 361 (2003):
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1. 0.7 2000 total kcal/day 1400 kcal from
carbohydrate/day
1400 kcal from carbohydrate 4 kcal/g 350 g carbohydrate
This carbohydrate intake is higher than the Daily Value and higher
than the 45 to 65 percent recommendation.
2. 350 g carbohydrate 2 175 g carbohydrate/day
175 g carbohydrate 4 kcal/g 700 kcal from carbohydrate
700 kcal from carbohydrate 2000 total kcal/day 0.35
0.35 100 35% kcal from carbohydrate
This carbohydrate intake is lower than the Daily Value and lower
than the 45 to 65 percent recommendation.
3. 350 g carbohydrate 2 700 g carbohydrate/day
700 g carbohydrate 4 kcal/g 2800 kcal from carbohydrate
This carbohydrate intake is higher than the Daily Value and meets
the 45 to 65 percent recommendation.
4. 150 g carbohydrate 4 kcal/g 600 kcal from carbohydrate
This carbohydrate intake is lower than the Daily Value and meets
the 45 to 65 percent recommendation.
1. b 2. c 3. c 4. d 5. d
6. b 7. d 8. d 9. a 10. d
ANSWERS

HIGHLIGHT 4
Alternatives to Sugar
132
Almost everyone finds pleasure in sweet
foods—after all, the taste preference for sweets
is inborn. To a child, the sweeter the food, the
better. In adults, this preference is somewhat
diminished, but most adults still enjoy an occa-
sional sweet food or beverage. Because they
want to control weight gain, blood glucose,
and dental caries, many consumers turn to al-
ternative sweeteners to help them limit kcalories and minimize
sugar intake. In doing so, they encounter two sets of alternative
sweeteners: artificial sweeteners and sugar replacers.
Artificial Sweeteners
The Food and Drug Administration (FDA) has approved the use of
several artificial sweeteners—saccharin, aspartame, acesulfame
potassium (acesulfame-K), sucralose, and neotame. Two others are
awaiting FDA approval—alitame and cyclamate. Another—
tagatose—did not need approval because it is generally recognized
as a safe ingredient. These artificial sweeteners are sometimes called
nonnutritive sweeteners because they provide virtually no en-
ergy. Table H4-1 and the accompanying glossary provide general
details about each of these sweeteners.
Saccharin, acesulfame-K, and sucralose are
not metabolized in the body; in contrast, the
body digests aspartame as a protein. In fact,
aspartame yields energy (4 kcalories per
gram, as does protein), but because so little is
used, its energy contribution is negligible.
Some consumers have challenged the
safety of using artificial sweeteners. Considering that all sub-
stances are toxic at some dose, it is little surprise that large doses
of artificial sweeteners (or their components or metabolic by-
products) have toxic effects. The question to ask is whether their
ingestion is safe for human beings in quantities people normally
use (and potentially abuse).
Saccharin
Saccharin, used for over 100 years in the United States, is cur-
rently used by some 50 million people—primarily in soft drinks,
secondarily as a tabletop sweetener. Saccharin is rapidly excreted
in the urine and does not accumulate in the body.
Questions about saccharin’s safety surfaced in 1977, when ex-
periments suggested that large doses of saccharin (equivalent to
Funnette
Division,
Hoechst
Celenese
Corp.
Acceptable Daily Intake (ADI):
the estimated amount of a
sweetener that individuals can
safely consume each day over
the course of a lifetime without
adverse effect.
acesulfame (AY-sul-fame)
potassium: an artificial
sweetener composed of an
organic salt that has been
approved for use in both the
United States and Canada; also
known as acesulfame-K
because K is the chemical
symbol for potassium.
alitame (AL-ih-tame): an artificial
sweetener composed of two
amino acids (alanine and aspartic
acid); FDA approval pending.
artificial sweeteners: sugar
substitutes that provide
negligible, if any, energy;
sometimes called nonnutritive
sweeteners.
aspartame (ah-SPAR-tame or
ASS-par-tame): an artificial
sweetener composed of two
amino acids (phenylalanine and
aspartic acid); approved for use
in both the United States and
Canada.
cyclamate (SIGH-kla-mate): an
artificial sweetener that is being
considered for approval in the
United States and is available in
Canada as a tabletop sweetener,
but not as an additive.
neotame (NEE-oh-tame): an
artificial sweetener composed of
two amino acids (phenylalanine
and aspartic acid); approved for
use in the United States.
nonnutritive sweeteners:
sweeteners that yield no energy
(or insignificant energy in the
case of aspartame).
nutritive sweeteners: sweeteners
that yield energy, including
both sugars and sugar replacers.
saccharin (SAK-ah-ren): an
artificial sweetener that has
been approved for use in the
United States. In Canada,
approval for use in foods and
beverages is pending; currently
available only in pharmacies and
only as a tabletop sweetener,
not as an additive.
stevia (STEE-vee-ah): a South
American shrub whose leaves are
used as a sweetener; sold
in the United States as a
dietary supplement that provides
sweetness without kcalories.
sucralose (SUE-kra-lose): an
artificial sweetener approved for
use in the United States and
Canada.
sugar replacers: sugarlike
compounds that can be derived
from fruits or commercially
produced from dextrose; also
called sugar alcohols or
polyols. Sugar alcohols are
absorbed more slowly than
other sugars and metabolized
differently in the human body;
they are not readily utilized by
ordinary mouth bacteria.
Examples are maltitol,
mannitol, sorbitol, xylitol,
isomalt, and lactitol.
tagatose (TAG-ah-tose): a
monosaccharide structurally
similar to fructose that is
incompletely absorbed and thus
provides only 1.5 kcalories per
gram; approved for use as a
“generally recognized as safe”
ingredient.
GLOSSARY

hundreds of cans of diet soda daily for a lifetime) increased the
risk of bladder cancer in rats. The FDA proposed banning saccha-
rin as a result. Public outcry in favor of saccharin was so loud,
however, that Congress imposed a moratorium on the ban while
additional safety studies were conducted. Products containing
saccharin were required to carry a warning label until 2001, when
studies concluded that saccharin did not cause cancer in humans.
Does saccharin cause cancer? The largest population study to
date, involving 9000 men and women, showed that overall sac-
charin use did not increase the risk of cancer. Among certain small
groups of the population, however, such as those who both
smoked heavily and used saccharin, the risk of bladder cancer was
slightly greater. Other studies involving more than 5000 people
with bladder cancer showed no association between bladder can-
cer and saccharin use. In 2000, saccharin was removed from the
list of suspected cancer-causing substances. Warning labels are no
longer required.
Common sense dictates that consuming large amounts of any
substance is probably not wise, but at current, moderate intake
levels, saccharin appears to be safe for most people. It has been
approved for use in more than 100 countries.
Aspartame
Aspartame is a simple chemical compound made of compo-
nents common to many foods: two amino acids (phenylalanine
and aspartic acid) and a methyl group (CH3). Figure H4-1
(p. 134) shows its chemical structure. The flavors of the compo-
nents give no clue to the combined effect; one of them tastes bit-
ter, and the other is tasteless, but the combination creates a
product that is 200 times sweeter than sucrose.
In the digestive tract, enzymes split aspartame into its three
component parts. The body absorbs the two amino acids and
uses them just as if they had come from food protein, which is
made entirely of amino acids, including these two.
Because this sweetener contributes phenylalanine, products
containing aspartame must bear a warning label for people with
the inherited disease phenylketonuria (PKU). People with PKU are
unable to dispose of any excess phenylalanine. The accumulation
of phenylalanine and its by-products is toxic to the developing
nervous system, causing irreversible brain damage. For this rea-
son, all newborns in the United States are screened for PKU. The
treatment for PKU is a special diet that must strike a balance,
ALTERNATIVES TO SUGAR • 133
TABLE H4-1 Sweeteners
Average Amount
Relative Energy Acceptable to Replace
Sweeteners Sweetnessa (kcal/g) Daily Intake 1 tsp Sugar Approved Uses
Approved Sweeteners
(Trade Name)
Saccharin (Sweet ‘n Low) 450 0 5 mg/kg body weight 12 mg Tabletop sweeteners, wide range of foods,
beverages, cosmetics, and pharmaceutical
products
Aspartame (Nutrasweet, 200 4b 50 mg/kg body weightc 18 mg General purpose sweetener in all foods and
Equal, NutraTaste) beverages
Warning to people with PKU: Contains
phenylalanine
Acesulfame potassium or 200 0 15 mg/kg body weightd 25 mg Tabletop sweeteners, puddings, gelatins,
Acesulfame-K (Sunette, chewing gum, candies, baked goods, desserts,
Sweet One, Sweet ‘n Safe) beverages
Sucralose 600 0 5 mg/kg body weight 6 mg General purpose sweetener for all foods
(Splenda)
Neotame 8000 0 18 mg/day 0.5 μg Baked goods, nonalcoholic beverages, chew-
ing gum, candies, frostings, frozen desserts,
gelatins, puddings, jams and jellies, syrups
Tagatose 0.8 1.5 7.5 g/day 1 tsp Baked goods, beverages, cereals, chewing
(Nutralose) gum, confections, dairy products, dietary
supplements, health bars, tabletop sweetener
Sweeteners with Approval Pending Proposed Uses
Alitame 2000 4e — Beverages, baked goods, tabletop sweeteners,
frozen desserts
Cyclamate 30 0 — Tabletop sweeteners, baked goods
a Relative sweetness is determined by comparing the approximate sweetness of a sugar substitute
with the sweetness of pure sucrose, which has been defined as 1.0. Chemical structure, tempera-
ture, acidity, and other flavors of the foods in which the substance occurs all influence relative
sweetness.
b Aspartame provides 4 kcalories per gram, as does protein, but because so little is used, its
energy contribution is negligible. In powdered form, it is sometimes mixed with lactose, however,
so a 1-gram packet may provide 4 kcalories.
c Recommendations from the World Health Organization and in Europe and Canada limit aspar-
tame intake to 40 milligrams per kilogram of body weight per day.
d Recommendations from the World Health Organization limit acesulfame-K intake to 9 milligrams
per kilogram of body weight per day.
e Alitame provides 4 kcalories per gram, as does protein, but because so little is used, its energy
contribution is negligible.

providing enough phenylalanine to support normal growth and
health but not enough to cause harm. The little extra phenylala-
nine from aspartame poses only a small risk, even in heavy users,
but children with PKU need to get all their required phenylalanine
from foods instead of from an artificial sweetener. The PKU diet
excludes such protein- and nutrient-rich foods as milk, meat, fish,
poultry, cheese, eggs, nuts, legumes, and many bread products.
Consequently, these children have difficulty obtaining the many
essential nutrients—such as calcium, iron, and the B vitamins—
found along with phenylalanine in these foods. Children with
PKU cannot afford to squander their limited phenylalanine al-
lowance on the phenylalanine of aspartame, which contributes
none of the associated vitamins or minerals essential for good
health and normal growth.
During metabolism, the methyl group momentarily becomes
methyl alcohol (methanol)—a potentially toxic compound (see Fig-
ure H4-2). This breakdown also occurs when aspartame-sweetened
beverages are stored at warm temperatures over time. The amount
of methanol produced may be safe to consume, but a person may
not want to, considering that the beverage has lost its sweetness. In
the body, enzymes convert methanol to formaldehyde, another
toxic compound. Finally, formaldehyde is broken down to carbon
dioxide. Before aspartame could be approved, the quantities of
these products generated during metabolism had to be deter-
mined, and they were found to fall below the threshold at which
they would cause harm. In fact, ounce for ounce, tomato juice
yields six times as much methanol as a diet soda.
A recent Italian study found that aspartame caused cancer in
female rats and fueled the controversies surrounding aspartame’s
safety.1 Statements from the FDA and others, however, indicate
that such a conclusion is not supported by the data.2 The only
valid scientific concern is that for people with epilepsy, excessive
intake of aspartame may decrease their threshold for seizures; this
does not appear to be a problem when intakes are within recom-
mended amounts.3
Acesulfame-K
Because acesulfame potassium (acesulfame-K) passes
through the body unchanged, it does not provide any energy nor
does it increase the intake of potassium. Acesulfame-K is ap-
proved for use in the United States, Canada, and more than 60
other countries.
Sucralose
Sucralose is unique among the artificial sweeteners in that it is
made from sugar that has had three of its hydroxyl (OH) groups
replaced by chlorine atoms. The result is an exceptionally stable
molecule that is much sweeter than sugar. Because the body does
not recognize sucralose as a carbohydrate, it passes through the
GI tract undigested and unabsorbed.
Neotame
Like aspartame, neotame also contains the amino acids pheny-
lalanine and aspartic acid and a methyl group. Unlike aspartame,
however, neotame has an additional side group attached. This
simple difference makes all the difference to people with PKU be-
cause it blocks the digestive enzymes that normally separate
phenylalanine and aspartic acid. Consequently, the amino acids
are not absorbed and neotame need not carry a warning for peo-
ple with PKU.
Tagatose
The FDA granted the fructose relative tagatose the status of
“generally recognized as safe,” making it available as a low-kcalorie
sweetener for a variety of foods and beverages. This monosaccha-
ride is naturally found in only a few foods, but it can be derived
from lactose. Unlike fructose or lactose, however, 80 percent of
134 • Highlight 4
N C C
H
H
H
H C H
C O
O H
N
H
C
H
C
H C H
C
C
C
C
C
C
H
H
O
O C H
H
H
Aspartic acid Phenylalanine Methyl
group
Amino acids
O
H
H
H
FIGURE H4-1 Structure of Aspartame
O C H
H
H
Aspartic
acid
Methyl
group
hydrolyzed
O C H
H
H
H
Methanol
Oxidized
O C H
H
Formaldehyde
Oxidized
O C
Carbon dioxide
O
Phenylalanine
FIGURE H4-2 Metabolism of Aspartame

tagatose remains unabsorbed until it reaches the large intestine.
There, bacteria ferment tagatose, releasing gases and short chain
fatty acids that are absorbed. As a result, tagatose provides 1.5
kcalories per gram. At high doses, tagatose causes flatulence,
rumbling, and loose stools; otherwise, no adverse side effects
have been noted. In fact, tagatose is a prebiotic that may benefit
GI health. Unlike other sugars, tagatose does not promote dental
caries and may carry a dental caries health claim.
Alitame and Cyclamate
FDA approval for alitame and cyclamate is still pending. To
date, no safety issues have been raised for alitame, and it has been
approved for use in other countries. In contrast, cyclamate has
been battling safety issues for 50 years. Approved by the FDA in
1949, cyclamate was banned in 1969 principally on the basis of
one study indicating that it caused bladder cancer in rats.
The National Research Council has reviewed dozens of studies
on cyclamate and concluded that neither cyclamate nor its
metabolites cause cancer. The council did, however, recommend
further research to determine if heavy or long-term use poses
risks. Although cyclamate does not initiate cancer, it may promote
cancer development once it is started. The FDA currently has no
policy on substances that enhance the cancer-causing activities of
other substances, but it is unlikely to approve cyclamate soon, if
at all. Agencies in more than 50 other countries, including
Canada, have approved cyclamate.
Acceptable Daily Intake
The amount of artificial sweetener considered safe for daily use is
called the Acceptable Daily Intake (ADI). The ADI represents
the level of consumption that, if maintained every day through-
out a person’s life, would still be considered safe by a wide mar-
gin. It usually reflects an amount 100 times less than the level at
which no observed effects occur in animal research studies.
The ADI for aspartame, for example, is 50 milligrams per kilo-
gram of body weight. That is, the FDA approved aspartame based
on the assumption that no one would consume more than 50
milligrams per kilogram of body weight in a day. This maximum
daily intake is indeed high: for a 150-pound adult, it adds up to
97 packets of Equal or 20 cans of soft drinks sweetened only with
aspartame. The company that produces aspartame estimates that
if all the sugar and saccharin in the U.S. diet were replaced with
aspartame, 1 percent of the population would be consuming the
FDA maximum. Most people who use aspartame consume less
than 5 milligrams per kilogram of body weight per day. But a
young child who drinks four glasses of aspartame-sweetened bev-
erages on a hot day and has five servings of other products with
aspartame that day (such as pudding, chewing gum, cereal, gel-
atin, and frozen desserts) consumes the FDA maximum level. Al-
though this intake presents no proven hazard, it seems wise to
offer children other foods so as not to exceed the limit. Table H4-
2 lists the average amounts of aspartame in some common foods.
For persons choosing to use artificial sweeteners, the American
Dietetic Association wisely advises that they be used in modera-
tion and only as part of a well-balanced nutritious diet.4 The di-
etary principles of moderation and variety help to reduce the pos-
sible risks associated with any food.
Artificial Sweeteners and Weight Control
The rate of obesity in the United States has been rising for
decades. Foods and beverages sweetened with artificial sweeten-
ers were among the first products developed to help people con-
trol their weight. Ironically, a few studies have reported that
intense sweeteners, such as aspartame, may stimulate appetite,
which could lead to weight gain. Contradicting these reports,
most studies find no change in feelings of hunger and no change
in food intakes or body weight. Adding to the confusion, some
studies report lower energy intakes and greater weight losses
when people eat or drink artificially sweetened products.5
When studying the effects of artificial sweeteners on food in-
take and body weight, researchers ask different questions and
take different approaches. It matters, for example, whether the
people used in a study are of a healthy weight and whether they
are following a weight-loss diet. Motivations for using sweeteners
differ, too, and this influences a person’s actions. For example,
one person might drink an artificially sweetened beverage now so
as to be able to eat a high-kcalorie food later. This person’s energy
intake might stay the same or increase. A person trying to control
food energy intake might drink an artificially sweetened beverage
now and choose a low-kcalorie food later. This plan would help
reduce the person’s total energy intake.
In designing experiments on artificial sweeteners, researchers
have to distinguish between the effects of sweetness and the effects
of a particular substance. If a person is hungry shortly after eating
an artificially sweetened snack, is that because the sweet taste (of all
sweeteners, including sugars) stimulates appetite? Or is it because
the artificial sweetener itself stimulates appetite? Research must also
distinguish between the effects of food energy and the effects of
the substance. If a person is hungry shortly after eating an artificially
sweetened snack, is that because less food energy was available to
satisfy hunger? Or is it because the artificial sweetener itself triggers
hunger? Furthermore, if appetite is stimulated and a person feels
hungry, does that actually lead to increased food intake?
Whether a person compensates for the energy reduction of ar-
tificial sweeteners either partially or fully depends on several fac-
tors. Using artificial sweeteners will not automatically lower
energy intake; to control energy intake successfully, a person
needs to make informed diet and activity decisions throughout
the day (as Chapter 9 explains).
Food Aspartame (mg)
12 oz diet soft drink 170
8 oz powdered drink 100
8 oz sugar-free fruit yogurt 124
4 oz gelatin dessert 80
1 packet sweetener 35
TABLE H4-2 Average Aspartame Contents of Selected
Foods

Stevia—An Herbal
Alternative
The FDA has backed its approval or denial of artificial sweeteners
with decades of extensive research. Such research is lacking for
the herb stevia, a shrub whose leaves have long been used by
the people of South America to sweeten their beverages. In the
United States, stevia is sold in health-food stores as a dietary sup-
plement. The FDA has reviewed the limited research on the use of
stevia as an alternative to artificial sweeteners and found concerns
regarding its effect on reproduction, cancer development, and
energy metabolism. Used sparingly, stevia may do little harm, but
the FDA could not approve its extensive and widespread use in
the U.S. market. The European Union and the United Nations
have reached similar conclusions. In Canada, provisional guide-
lines have been adopted for the use of stevia as a medicinal ingre-
dient and as a sweetening agent. That stevia can be sold as a
dietary supplement but not used as a food additive in the United
States, highlights key differences in FDA regulations. Food addi-
tives must prove their safety and effectiveness before receiving
FDA approval, whereas dietary supplements are not required to
submit to any testing or receive any approval. (See Highlight 10
for information on dietary supplements and Chapter 19 for more
on herbs.)
Sugar Replacers
Some “sugar-free” or reduced-kcalorie products contain sugar re-
placers.* The term sugar replacers describes the sugar alcohols—
familiar examples include erythritol, mannitol, sorbitol, xylitol,
maltitol, isomalt, and lactitol—that provide bulk and sweetness in
cookies, hard candies, sugarless gums, jams, and jellies. These
products claim to be “sugar-free” on their labels, but in this case,
“sugar-free” does not mean free of kcalories. Sugar replacers do
provide kcalories, but fewer than their carbohydrate cousins, the
sugars. Because sugar replacers yield energy, they are sometimes
referred to as nutritive sweeteners. Table H4-3 includes their
energy values, but a simple estimate can help consumers: divide
grams by 2. Sugar alcohols occur naturally in fruits and vegeta-
bles; manufacturers also use sugar alcohols as a low-energy bulk
ingredient in many processed foods.
Sugar alcohols evoke a low glycemic response. The body ab-
sorbs sugar alcohols slowly; consequently, they are slower to en-
ter the bloodstream than other sugars. Side effects such as gas,
abdominal discomfort, and diarrhea, however, make them less at-
tractive than the artificial sweeteners. For this reason, regulations
require food labels to state “Excess consumption may have a lax-
ative effect” if reasonable consumption of that food could result
in the daily ingestion of 50 grams of a sugar alcohol.
The real benefit of using sugar replacers is that they do not
contribute to dental caries. Bacteria in the mouth cannot metab-
olize sugar alcohols as rapidly as sugar. They are therefore valu-
able in chewing gums, breath mints, and other products that
people keep in their mouths for a while. Figure H4-3 presents la-
beling information for products using sugar alternatives.
The sugar replacers, like the artificial sweeteners, can occupy a
place in the diet, and provided they are used in moderation, they
will do no harm. In fact, they can help, both by providing an al-
ternative to sugar for people with diabetes and by inhibiting
caries-causing bacteria. People may find it appropriate to use all
three sweeteners at times: artificial sweeteners, sugar replacers,
and sugar itself.
136 • Highlight 4
Sugar Relative Energy
Alcohols Sweetnessa (kcal/g) Approved Uses
Erythritol 0.7 0.4 Beverages, frozen dairy
desserts, baked goods,
chewing gum, candies
Isomalt 0.5 2.0 Candies, chewing gum,
ice cream, jams and
jellies, frostings, bever-
ages, baked goods
Lactitol 0.4 2.0 Candies, chewing gum,
frozen dairy desserts,
jams and jellies, frost-
ings, baked goods
Maltitol 0.9 2.1 Particularly good for
candy coating
Mannitol 0.7 1.6 Bulking agent, chewing
gum
Sorbitol 0.5 2.6 Special dietary foods,
candies, gums
Xylitol 1.0 2.4 Chewing gum, candies,
pharmaceutical and oral
health products
a Relative sweetness is determined by comparing the approximate sweetness of a sugar
replacer with the sweetness of pure sucrose, which has been defined as 1.0. Chemical
structure, temperature, acidity, and other flavors of the foods in which the substance occurs
all influence relative sweetness.
* To minimize confusion, the American Diabetes Association prefers the term
sugar replacers instead of “sugar alcohols” (which connotes alcohol), “bulk
sweeteners” (which connotes fiber), or “sugar substitutes” (which connotes
aspartame and saccharin).
TABLE H4-3 Sugar Replacers

Total Fat 0g 0%
*Percent Daily Values (DV) are
based on a 2,000 calorie diet.
Serving Size 2 pieces (3g)
Servings 6
Calories 5
35% FEWER CALORIES THAN SUGARED GUM.
INGREDIENTS: SORBITOL, MALTITOL, GUM BASE, MANNITOL, ARTIFICIAL AND NATURAL FLAVORING, ACACIA,
SOFTENERS, TITANIUM DIOXIDE (COLOR), ASPARTAME, ACESULFAME POTASSIUM AND CANDELILLA WAX.
PHENYLKETONURICS: CONTAINS PHENYLALANINE.
Amount per serving % DV*
Sodium 0mg 0%
1%
Protein 0g
Sugar Alcohol 2g
Not a significant source
of other nutrients.
Sugars 0g
Total Carb. 2g
Nutrition
Facts
Products containing
sugar replacers may
claim to “not promote
tooth decay” if they
meet FDA criteria for
dental plaque activity.
This ingredient list
includes both sugar
alcohols and artificial
sweetenters.
Products that claim to be
“reduced kcalories” must
provide at least 25%
fewer kcalories per serving
than the comparison item.
Products containing
less than 0.5 g of
sugar per serving can
claim to be “sugarless”
or “sugar-free.”
Products containing
aspartame must carry
a warning for people
with phenylketonuria.
FIGURE H4-3 Sugar Alternatives on Food Labels
• Search for “artificial sweeteners” at the U.S. Government
• Search for “sweeteners” at the International Food
Information Council site: www.ific.org
1. M. Soffritti and coauthors, Aspartame in-
duces lymphomas and leukaemias in rats,
European Journal of Oncology 10 (2005):
107–116.
2. U.S. Food and Drug Administration, FDA
statement on European aspartame study,
posted May 8, 2006, www.fda.gov; M. R.
Weihrauch and V. Diehl, Artificial sweeten-
ers—Do they bear a carcinogenic risk?
Annals of Oncology 15 (2004): 1460–1465.
3. S. M. Jankovic, Controversies with aspar-
tame, Medicinski Pregled 56 (2003): 27–29.
tion: Use of nutritive and nonnutritive
sweeteners, Journal of the American Dietetic
Association 104 (2004): 255–275.
5. S. H. F. Vermunt and coauthors, Effects of
sugar intake on body weight: A review,
Obesity Reviews 4 (2003): 91–99.
REFERENCES
©
Craig
Moore

Most likely, you know what you don’t like about body fat, but do you appreciate
how it insulates you against the cold or powers your hike around a lake? And
what about food fat? You’re right to credit fat for providing the delicious flavors
and aromas of buttered popcorn and fried chicken—and to criticize it for
contributing to the weight gain and heart disease so common today. The
challenge is to strike a healthy balance of enjoying some fat, but not too much.
Learning which kinds of fats are most harmful will help you make wise decisions.
The CengageNOW logo
Animated! Figure 5.17: Absorption of Fat
Michael Paul/Getty Images

Most people are surprised to learn that fat has some virtues. Only when
people consume either too much or too little fat, or too much of some kinds
of fat, does poor health develop. It is true, though, that in our society of
abundance, people are likely to consume too much fat.
Fat refers to the class of nutrients known as lipids. The lipid family in-
cludes triglycerides (fats and oils), phospholipids, and sterols. The triglyc-
erides ◆ predominate, both in foods and in the body.
The Chemist’s View of Fatty Acids
and Triglycerides
Like carbohydrates, fatty acids and triglycerides are composed of carbon (C), hydro-
gen (H), and oxygen (O). Because these lipids have many more carbons and hydro-
gens in proportion to their oxygens, however, they can supply more energy per
gram than carbohydrates can (Chapter 7 provides details).
The many names and relationships in the lipid family can seem overwhelm-
ing—like meeting a friend’s extended family for the first time. To ease the introduc-
tions, this chapter first presents each of the lipids from a chemist’s point of view
using both words and diagrams. Then the chapter follows the lipids through diges-
tion and absorption and into the body to examine their roles in health and disease.
For people who think more easily in words than in chemical symbols, this preview
of the upcoming chemistry may be helpful:
1. Every triglyceride contains one molecule of glycerol and three fatty acids (basi-
cally, chains of carbon atoms).
2. Fatty acids may be 4 to 24 (even numbers of) carbons long, the 18-carbon ones
being the most common in foods and especially noteworthy in nutrition.
3. Fatty acids may be saturated or unsaturated. Unsaturated fatty acids may have
one or more points of unsaturation. (That is, they may be monounsaturated or
polyunsaturated.)
4. Of special importance in nutrition are the polyunsaturated fatty acids whose
first point of unsaturation is next to the third carbon (known as omega-3 fatty
acids) or next to the sixth carbon (omega-6).
5. The 18-carbon fatty acids that fit this description are linolenic acid (omega-3) and
linoleic acid (omega-6). Each is the primary member of a family of longer-chain
CHAPTER OUTLINE
The Chemist’s View of Fatty Acids
and Triglycerides • Fatty Acids •
Triglycerides • Degree of Unsaturation
Revisited
The Chemist’s View of Phospholipids
and Sterols • Phospholipids • Sterols
Digestion, Absorption, and Transport
of Lipids • Lipid Digestion • Lipid
Absorption • Lipid Transport •
Lipids in the Body • Roles of Triglyc-
erides • Essential Fatty Acids • A Preview
of Lipid Metabolism
Intakes of Lipids • Health Effects of
Lipids • Recommended Intakes of Fat •
HIGHLIGHT 5 High-Fat Foods—Friend
or Foe?
5
The Lipids:
Triglycerides,
Phospholipids,
and Sterols
C H A P T E R
◆ Of the lipids in foods, 95% are fats and oils
(triglycerides); of the lipids stored in the
body, 99% are triglycerides.
lipids: a family of compounds that includes
triglycerides, phospholipids, and sterols.
Lipids are characterized by their insolubility in
water. (Lipids also include the fat-soluble vita-
mins, described in Chapter 11.)
fats: lipids that are solid at room temperature
(77°F or 25°C).
oils: lipids that are liquid at room temperature
(77°F or 25°C).
139

140 • CHAPTER 5
fatty acids that help to regulate blood pressure, blood clotting, and other body
functions important to health.
The paragraphs, definitions, and diagrams that follow present this information
again in much more detail.
Fatty Acids
A fatty acid is an organic acid—a chain of carbon atoms with hydrogens at-
tached—that has an acid group (COOH) at one end and a methyl group (CH3) at
the other end. The organic acid shown in Figure 5-1 is acetic acid, the compound
that gives vinegar its sour taste. Acetic acid is the shortest such acid, with a “chain”
only two carbon atoms long.
The Length of the Carbon Chain Most naturally occurring fatty acids contain
even numbers of carbons in their chains—up to 24 carbons in length. This discus-
sion begins with the 18-carbon fatty acids, which are abundant in our food supply.
Stearic acid is the simplest of the 18-carbon fatty acids; the bonds between its car-
bons are all alike:
As you can see, stearic acid is 18 carbons long, and each atom meets the rules of
chemical bonding described in Figure 4-1 on p. 102. The following structure also de-
picts stearic acid, but in a simpler way, with each “corner” on the zigzag line repre-
senting a carbon atom with two attached hydrogens:
As mentioned, the carbon chains of fatty acids vary in length. The long-chain
(12 to 24 carbons) fatty acids of meats, fish, and vegetable oils are most common
in the diet. Smaller amounts of medium-chain (6 to 10 carbons) and short-chain
(fewer than 6 carbons) fatty acids also occur, primarily in dairy products. (Tables C-
1 and C-2 in Appendix C provide the names, chain lengths, and sources of fatty
acids commonly found in foods.)
The Degree of Unsaturation Stearic acid is a saturated fatty acid (terms that
describe the saturation of fatty acids are defined in the accompanying glossary). A
saturated fatty acid is fully loaded with hydrogen atoms and contains only single
bonds between its carbon atoms. If two hydrogens were missing from the middle of
the carbon chain, the remaining structure might be:
Such a compound cannot exist, however, because two of the carbons have only
three bonds each, and nature requires that every carbon have four bonds. The two
carbons therefore form a double bond:
FIGURE 5-1 Acetic Acid
Acetic acid is a two-carbon organic acid.
C C OH
H
H
O
H
Methyl
end
Acid
end
H C C
H
H
H
H
C
H
H
C
H
C C
H
H
H
H
C
H
C
H
H
C
H
C C
H
H
H
H
C C
H
H
H
H
C
H
H
H
C
O
O H
C C
H
H
H
H
C
H
H H H
H C
H
H
C O H
O
H C C
H
H
H
H
C
H
H
C
H
C C
H
H
H
H
C
H
C
H
H
C
H
C C
H
H
H
H
C C
H
H
H
H
C
H
H
H
C
O
O H
C C
H
H
H
H
C
H
H
H C C
H
H
H
H
C
H
H
C
H
C C
H
H
H
H
C
H
C
H
H
C C
H
H
H
C C
H
H
H
H
C C
H
H
H
H
H
C
O
O H
C C
H
H
H
H
C
H
H
Stearic acid, an 18-carbon saturated fatty acid
Stearic acid (simplified structure)
An impossible chemical structure
Oleic acid, an 18-carbon monounsaturated fatty
acid

THE LIPIDS: TRIGLYCERIDES, PHOSPHOLIPIDS, AND STEROLS • 141
The same structure drawn more simply looks like this: ◆
The double bond is a point of unsaturation. Hence, a fatty acid like this—with
two hydrogens missing and a double bond—is an unsaturated fatty acid. This
one is the 18-carbon monounsaturated fatty acid oleic acid, which is abundant
in olive oil and canola oil.
A polyunsaturated fatty acid has two or more carbon-to-carbon double
bonds. Linoleic acid, the 18-carbon fatty acid common in vegetable oils, lacks
four hydrogens and has two double bonds:
Drawn more simply, linoleic acid looks like this (though the actual shape would
kink at the double bonds):
A fourth 18-carbon fatty acid is linolenic acid, which has three double bonds.
Table 5-1 presents the 18-carbon fatty acids. ◆
The Location of Double Bonds Fatty acids differ not only in the length of their
chains and their degree of saturation, but also in the locations of their double bonds.
Chemists identify polyunsaturated fatty acids by the position of the double bond
nearest the methyl (CH3) end of the carbon chain, which is described by an omega
number. A polyunsaturated fatty acid with its first double bond three carbons away
H C C
H
H
H
H
C
H
H
C
H
C C
H
H
H
H
C
H
C C
H
H
C
H
H
C C
H
H
H
C C
H
H
H
H
C C
H
H
H
H
C
H
H
H
C
O
O H
H C
H
H
C
O
O H
◆ Chemists use a shorthand notation to
describe fatty acids. The first number
indicates the number of carbon atoms; the
second, the number of the double bonds. For
example, the notation for stearic acid is 18:0.
fatty acid: an organic compound
composed of a carbon chain
with hydrogens attached and an
acid group (COOH) at one end
and a methyl group (CH3) at the
other end.
monounsaturated fatty acid
(MUFA): a fatty acid that lacks
two hydrogen atoms and has
one double bond between
carbons—for example, oleic
acid. A monounsaturated fat is
composed of triglycerides in
which most of the fatty acids are
monounsaturated.
• mono one
point of unsaturation: the
double bond of a fatty acid,
where hydrogen atoms can
easily be added to the structure.
polyunsaturated fatty acid
(PUFA): a fatty acid that lacks
four or more hydrogen atoms
and has two or more double
bonds between carbons—for
example, linoleic acid (two
double bonds) and linolenic
acid (three double bonds). A
polyunsaturated fat is
composed of triglycerides in
which most of the fatty acids are
polyunsaturated.
• poly many
saturated fatty acid: a fatty acid
carrying the maximum possible
number of hydrogen atoms—
for example, stearic acid. A
saturated fat is composed of
triglycerides in which most of
the fatty acids are saturated.
unsaturated fatty acid: a fatty
acid that lacks hydrogen atoms
and has at least one double bond
between carbons (includes
monounsaturated and
polyunsaturated fatty acids). An
unsaturated fat is composed of
triglycerides in which most of the
fatty acids are unsaturated.
GLOSSARY OF FATTY ACID TERMS
TABLE 5-1 18-Carbon Fatty Acids
Number of Number of Common
Name Carbon Atoms Double Bonds Saturation Food Sources
Stearic acid 18 0 Saturated Most animal fats
Oleic acid 18 1 Monounsaturated Olive, canola oils
Linoleic acid 18 2 Polyunsaturated Sunflower, safflower,
corn, and soybean oils
Linolenic acid 18 3 Polyunsaturated Soybean and canola
oils, flaxseed, walnuts
linoleic (lin-oh-LAY-ick) acid: an essential
fatty acid with 18 carbons and two double
bonds.
linolenic (lin-oh-LEN-ick) acid: an essential
fatty acid with 18 carbons and three double
bonds.
omega: the last letter of the Greek alphabet
(ω), used by chemists to refer to the position
of the first double bond from the methyl
(CH3) end of a fatty acid.
H C
H
H
C
O
O H
◆ Remember that each “corner” on the zigzag
line represents a carbon atom with two
attached hydrogens. In addition, although
drawn straight here, the actual shape kinks
at the double bonds (as shown in the left
side of Figure 5-8).
Oleic acid (simplified structure)
Linoleic acid, an 18-carbon polyunsaturated fatty
acid
Linoleic acid (simplified structure)

142 • CHAPTER 5
from the methyl end is an omega-3 fatty acid. Similarly, an omega-6 fatty acid
is a polyunsaturated fatty acid with its first double bond six carbons away from the
methyl end. Figure 5-2 compares two 18-carbon fatty acids—linolenic acid (an
omega-3 fatty acid) and linoleic acid (an omega-6 fatty acid).
Triglycerides
Few fatty acids occur free in foods or in the body. Most often, they are incorporated
into triglycerides—lipids composed of three fatty acids attached to a glycerol.
(Figure 5-3 presents a glycerol molecule.) To make a triglyceride, a series of conden-
sation reactions combine a hydrogen atom (H) from the glycerol and a hydroxyl
(OH) group from a fatty acid, forming a molecule of water (H2O) and leaving a bond
between the other two molecules (see Figure 5-4). Most triglycerides contain a mix-
ture of more than one type of fatty acid (see Figure 5-5).
Degree of Unsaturation Revisited
The chemistry of a fatty acid—whether it is short or long, saturated or unsatu-
rated, with its first double bond here or there—influences the characteristics of
foods and the health of the body. A section later in this chapter explains how these
features affect health; this section describes how the degree of unsaturation influ-
ences the fats and oils in foods.
Firmness The degree of unsaturation influences the firmness of fats at room tem-
perature. Generally speaking, the polyunsaturated vegetable oils are liquid at room
temperature, and the more saturated animal fats are solid. Not all vegetable oils are
polyunsaturated, however. Cocoa butter, palm oil, palm kernel oil, and coconut oil
◆ are saturated even though they are of vegetable origin; they are firmer than most
vegetable oils because of their saturation, but softer than most animal fats because
of their shorter carbon chains (8 to 14 carbons long). Generally, the shorter the car-
Omega carbon
H
H
C
H
H
H
C
H
Linolenic acid, an omega-3 fatty acid
Methyl end
Acid end
Methyl end
Linoleic acid, an omega-6 fatty acid
6
3
C
O
O H
Acid end
C
O
O H
Omega carbon
FIGURE 5-2 Omega-3 and Omega-6 Fatty Acids Compared
The omega number indicates the position of the first double bond in a fatty acid,
counting from the methyl (CH3) end. Thus an omega-3 fatty acid’s first double
bond occurs three carbons from the methyl end, and an omega-6 fatty acid’s first
double bond occurs six carbons from the methyl end. The members of an omega
family may have different lengths and different numbers of double bonds, but the
first double bond occurs at the same point in all of them. These structures are
drawn linearly here to ease counting carbons and locating double bonds, but their
shapes actually bend at the double bonds, as shown in Figure 5-8 (p. 145).
C O H
H
H
C O H
H
C O H
H
H
FIGURE 5-3 Glycerol
When glycerol is free, an OH group is
attached to each carbon. When glycerol is
part of a triglyceride, each carbon is attached
to a fatty acid by a carbon-oxygen bond.
◆ The food industry often refers to these satu-
rated vegetable oils as the “tropical oils.”
omega-3 fatty acid: a polyunsaturated fatty
acid in which the first double bond is three
carbons away from the methyl (CH3) end of
the carbon chain.
omega-6 fatty acid: a polyunsaturated fatty
acid in which the first double bond is six
carbons from the methyl (CH3) end of the
carbon chain.
triglycerides (try-GLISS-er-rides): the chief
form of fat in the diet and the major storage
form of fat in the body; composed of a
molecule of glycerol with three fatty acids
attached; also called triacylglycerols (try-
ay-seel-GLISS-er-ols).*
• tri = three
• glyceride = of glycerol
• acyl = a carbon chain
glycerol (GLISS-er-ol): an alcohol composed
of a three-carbon chain, which can serve as
the backbone for a triglyceride.
• ol = alcohol
* Research scientists commonly use the term triacylglycerols; this book continues to use the more famil-
iar term triglycerides, as do many other health and nutrition books and journals.

bon chain, the softer the fat is at room temperature. Fatty acid compositions of se-
lected fats and oils are shown in Figure 5-6 (p. 144), and Appendix H provides the
fat and fatty acid contents of many other foods.
Stability Saturation also influences stability. All fats become spoiled when ex-
posed to oxygen. Polyunsaturated fats spoil most readily because their double bonds
are unstable; monounsaturated fats are slightly less susceptible. Saturated fats are
most resistant to oxidation and thus least likely to become rancid. The oxidation
of fats produces a variety of compounds that smell and taste rancid; other types of
spoilage can occur due to microbial growth.
Manufacturers can protect fat-containing products against rancidity in three
ways—none of them perfect. First, products may be sealed in air-tight, nonmetallic
containers, protected from light, and refrigerated—an expensive and inconvenient
storage system. Second, manufacturers may add antioxidants to compete for the
oxygen and thus protect the oil (examples are the additives BHA and BHT and vita-
min E).* Third, manufacturers may saturate some or all of the points of unsaturation
by adding hydrogen molecules—a process known as hydrogenation.
Hydrogenation Hydrogenation offers two advantages. First, it protects against
oxidation (thereby prolonging shelf life) by making polyunsaturated fats more sat-
urated (see Figure 5-7, p. 144). Second, it alters the texture of foods by making liquid
vegetable oils more solid (as in margarine and shortening). Hydrogenated fats make
margarine spreadable, pie crusts flaky, and puddings creamy.
Trans-Fatty Acids Figure 5-7 illustrates the total hydrogenation of a polyunsatu-
rated fatty acid to a saturated fatty acid, which rarely occurs during food processing.
Most often, a fat is partially hydrogenated, and some of the double bonds that re-
main after processing change from cis to trans. In nature, most double bonds are
cis—meaning that the hydrogens next to the double bonds are on the same side of
the carbon chain. Only a few fatty acids (notably a small percentage of those found
in milk and meat products) are trans-fatty acids—meaning that the hydrogens
next to the double bonds are on opposite sides of the carbon chain (see Figure 5-8,
p. 145).† These arrangements result in different configurations for the fatty acids,
and this difference affects function: in the body, trans-fatty acids that derive from
hydrogenation behave more like saturated fats than like unsaturated fats. The re-
lationship between trans-fatty acids and heart disease has been the subject of much
H C O
H
H C O
H C O
H
C
O
C
H
H
H
H H O
Triglyceride + 3 water molecules
Glycerol + 3 fatty acids
C
O
C
H
H
H
H O
C
O
C
H
H
H
H H O
H H C O
H
H C O
H C O
H
H2O
C
O
C
H
H
H
C
O
C
H
H
H
C
O
C
H
H
H
+
H2O
+
H2O
+
Three fatty acids attached to a glycerol form a triglyceride
and yield water. In this example, all three fatty acids are
stearic acid, but most often triglycerides contain mixtures
of fatty acids (as shown in Figure 5-5).
An H atom from glycerol and an OH group from a fatty acid
combine to create water, leaving the O on the glycerol and the
C at the acid end of each fatty acid to form a bond.
FIGURE 5-4 Condensation of Glycerol and Fatty Acids to Form a Triglyceride
To make a triglyceride, three fatty acids attach to glycerol in condensation reactions.
H
C
H
H
H C O
H
H C O
H C O
H
C
O
C
O
H
C
H
H
C
O
H
C
H
H
This mixed triglyceride includes a saturated
fatty acid, a monounsaturated fatty acid, and
a polyunsaturated fatty acid, respectively.
FIGURE 5-5 A Mixed Triglyceride
* BHA is butylated hydroxyanisole; BHT is butylated hydroxytoluene.
† For example, most dairy products contain less than 0.5 grams trans fat per serving.
oxidation (OKS-ee-day-shun): the process of
a substance combining with oxygen;
oxidation reactions involve the loss of
electrons.
antioxidants: as a food additive,
preservatives that delay or prevent rancidity
of fats in foods and other damage to food
caused by oxygen.
hydrogenation (HIGH-dro-jen-AY-shun or
high-DROJ-eh-NAY-shun): a chemical process
by which hydrogens are added to
monounsaturated or polyunsaturated fatty
acids to reduce the number of double
bonds, making the fats more saturated
(solid) and more resistant to oxidation
(protecting against rancidity). Hydrogenation
produces trans-fatty acids.
trans-fatty acids: fatty acids with hydrogens
on opposite sides of the double bond.

144 • CHAPTER 5
At room temperature, saturated fats (such as
those commonly found in butter and other
animal fats) are solid, whereas unsaturated
fats (such as those found in vegetable oils) are
usually liquid.
Coconut oil
Butter
Beef tallow
Palm oil
Animal fats and the tropical oils of coconut and palm are mostly saturated fatty acids.
Some vegetable oils, such as olive and canola, are rich in monounsaturated fatty acids.
Many vegetable oils are rich in polyunsaturated fatty acids.
Sunflower oil
Corn oil
Olive oil
Canola oil
Peanut oil
Lard
Key:
Saturated
Monounsaturated
Polyunsaturated,
omega-6
Polyunsaturated,
omega-3
Flaxseed oil
Walnut oil
Safflower oil
FIGURE 5-6 Comparison of Dietary Fats
Most fats are a mixture of saturated, monounsaturated, and polyunsaturated fatty acids.
C
H
H
H
C
O
O H C
H
H
H
O
O H
C
Polyunsaturated fatty acid Hydrogenated (saturated) fatty acid
H+
H+
H+
H+
FIGURE 5-7 Hydrogenation
Double bonds carry a slightly negative charge and readily accept positively charged
hydrogen atoms, creating a saturated fatty acid. Most often, fat is partially hydro-
genated, creating a trans-fatty acid (shown in Figure 5-8).
The predominant lipids both in foods and in the body are triglycerides: glyc-
erol backbones with three fatty acids attached. Fatty acids vary in the length
of their carbon chains, their degrees of unsaturation, and the location of their
double bond(s). Those that are fully loaded with hydrogens are saturated;
those that are missing hydrogens and therefore have double bonds are unsat-
urated (monounsaturated or polyunsaturated). The vast majority of triglyc-
erides contain more than one type of fatty acid. Fatty acid saturation affects
fats’ physical characteristics and storage properties. Hydrogenation, which
makes polyunsaturated fats more saturated, gives rise to trans-fatty acids, al-
tered fatty acids that may have health effects similar to those of saturated
fatty acids.
IN SUMMARY
recent research, as a later section describes. In contrast, naturally occurring fatty
acids, such as conjugated linoleic acid, that have a trans configuration may
have health benefits.1
conjugated linoleic acid: a collective term
for several fatty acids that have the same
chemical formula as linoleic acid (18
carbons, two double bonds) but with
different configurations.
©
Polara
Studios
Inc.

The Chemist’s View of Phospholipids
and Sterols
The preceding pages have been devoted to one of the three classes of lipids, the
triglycerides, and their component parts, the fatty acids. The other two classes of
lipids, the phospholipids and sterols, make up only 5 percent of the lipids in the diet.
Phospholipids
The best-known phospholipid is lecithin. A diagram of a lecithin molecule is
shown in Figure 5-9 (p. 146). Notice that lecithin has a backbone of glycerol with
two of its three attachment sites occupied by fatty acids like those in triglycerides.
The third site is occupied by a phosphate group and a molecule of choline. The
fatty acids make phospholipids soluble in fat; the phosphate group allows them to
dissolve in water. Such versatility enables the food industry to use phospholipids as
emulsifiers ◆ to mix fats with water in such products as mayonnaise and candy
bars.
Phospholipids in Foods In addition to the phospholipids used by the food indus-
try as emulsifiers, phospholipids are also found naturally in foods. The richest food
sources of lecithin are eggs, liver, soybeans, wheat germ, and peanuts.
Roles of Phospholipids The lecithins and other phospholipids are important
constituents of cell membranes (see Figure 5-10, p. 146). Because phospholipids are
soluble in both water and fat, they can help lipids move back and forth across the
cell membranes into the watery fluids on both sides. Thus they enable fat-soluble
substances, including vitamins and hormones, to pass easily in and out of cells. The
phospholipids also act as emulsifiers in the body, helping to keep fats suspended in
the blood and body fluids.
Lecithin periodically receives attention in the popular press. Its advocates claim
that it is a major constituent of cell membranes (true), that cell membranes are es-
sential to the integrity of cells (true), and that consumers must therefore take lecithin
supplements (false). The liver makes from scratch all the lecithin a person needs. As
for lecithin taken as a supplement, the digestive enzyme lecithinase ◆ in the intes-
tine hydrolyzes most of it before it passes into the body, so little lecithin reaches the
tissues intact. In other words, lecithin is not an essential nutrient; it is just another
cis-fatty acid trans-fatty acid
H
H
H
H
H
C
O
O H
C
H
H
C
O
O H
H C
H
H
A cis-fatty acid has its hydrogens on the same side
of the double bond; cis molecules fold back into a
U-like formation. Most naturally occuring unsaturated
fatty acids in foods are cis.
A trans-fatty acid has its hydrogens on the opposite sides
of the double bond; trans molecules are more linear. The
trans form typically occurs in partially hydrogenated foods
when hydrogen atoms shift around some double bonds
and change the configuration from cis to trans.
FIGURE 5-8 Cis- and Trans-Fatty Acids Compared
This example shows the cis configuration for an 18-carbon monounsaturated fatty acid (oleic acid) and its corresponding trans configuration
(elaidic acid).
◆ Reminder: Emulsifiers are substances with
both water-soluble and fat-soluble portions
that promote the mixing of oils and fats in
watery solutions.
◆ Reminder: The word ending -ase denotes an
enzyme. Hence, lecithinase is an enzyme
that works on lecithin.
phospholipid (FOS-foe-LIP-id): a compound
similar to a triglyceride but having a
phosphate group (a phosphorus-containing
salt) and choline (or another nitrogen-
containing compound) in place of one of
the fatty acids.
lecithin (LESS-uh-thin): one of the
phospholipids. Both nature and the food
industry use lecithin as an emulsifier to
combine water-soluble and fat-soluble
ingredients that do not ordinarily mix,
such as water and oil.
choline (KOH-leen): a nitrogen-containing
compound found in foods and made in
the body from the amino acid methionine.
Choline is part of the phospholipid lecithin
and the neurotransmitter acetylcholine.

146 • CHAPTER 5
lipid. Like other lipids, lecithin contributes 9 kcalories per gram—an unexpected
“bonus” many people taking lecithin supplements fail to realize. Furthermore,
large doses of lecithin may cause GI distress, sweating, and loss of appetite. Perhaps
these symptoms can be considered beneficial—if they serve to warn people to stop
self-dosing with lecithin.
H C O
H
H C O
H C O
H
C
O
C
O
P
O
O
–
H
C
H
H
H
C
H
O C
H
H
C
H
H
N
+
CH3
CH3
CH3
The plus charge on the N is
balanced by a negative ion—
usually chloride.
From phosphate
From glycerol
From choline
From 2
fatty acids
H
FIGURE 5-9 Lecithin
Lecithin is one of the phospholipids. Notice that a molecule of lecithin is similar to a
triglyceride but contains only two fatty acids. The third position is occupied by a phos-
phate group and a molecule of choline. Other phospholipids have different fatty acids
at the upper two positions and different groups attached to phosphate.
Glycerol heads
Outside cell
Inside cell
Fatty acid tails
Watery fluid
Watery fluid
FIGURE 5-10 Phospholipids of a Cell
Membrane
A cell membrane is made of phospholipids
assembled into an orderly formation called a
bilayer. The fatty acid “tails” orient themselves
away from the watery fluid inside and outside
of the cell. The glycerol and phosphate
“heads” are attracted to the watery fluid.
Phospholipids, including lecithin, have a unique chemical structure that al-
lows them to be soluble in both water and fat. In the body, phospholipids are
part of cell membranes; the food industry uses phospholipids as emulsifiers to
mix fats with water.
IN SUMMARY
Sterols
In addition to triglycerides and phospholipids, the lipids include the sterols, com-
pounds with a multiple-ring structure.* The most famous sterol is cholesterol; Fig-
ure 5-11 (p. 147) shows its chemical structure.
Sterols in Foods Foods derived from both plants and animals contain sterols, but
only those from animals contain significant amounts of cholesterol—meats, eggs,
fish, poultry, and dairy products. Some people, confused about the distinction be-
tween dietary ◆ and blood cholesterol, have asked which foods contain the “good”
cholesterol. “Good” cholesterol is not a type of cholesterol found in foods, but it refers
to the way the body transports cholesterol in the blood, as explained later (p. 152).
Sterols other than cholesterol are naturally found in all plants. Being struc-
turally similar to cholesterol, these plant sterols interfere with cholesterol absorp-
tion, thus lowering blood cholesterol levels.2 Food manufacturers have fortified
foods such as margarine with plant sterols, creating a functional food that helps to
reduce blood cholesterol.
* The four-ring core structure identifies a steroid; sterols are alcohol derivatives with a steroid ring
structure.
sterols (STARE-ols or STEER-ols): compounds
containing a four ring carbon structure with
any of a variety of side chains attached.
cholesterol (koh-LESS-ter-ol): one of the
sterols containing a four ring carbon
structure with a carbon side chain.
Water
Oil
Without help from emulsifiers, fats and water
don’t mix.
Matthew
Farruggio
◆ The chemical structure is the same, but cho-
lesterol that is made in the body is called en-
dogenous (en-DOGDE-eh-nus), whereas
cholesterol from outside the body (from
foods) is called exogenous (eks-ODGE-eh-
nus).
• endo = within
• gen = arising
• exo = outside (the body)

Roles of Sterols Many vitally important body compounds are sterols. Among
them are bile acids, the sex hormones (such as testosterone), the adrenal hormones
(such as cortisol), and vitamin D, as well as cholesterol itself. Cholesterol in the body
can serve as the starting material for the synthesis of these compounds ◆ or as a
structural component of cell membranes; more than 90 percent of all the body’s cho-
lesterol resides in the cells. Despite popular impressions to the contrary, cholesterol
is not a villain lurking in some evil foods—it is a compound the body makes and
uses. Right now, as you read, your liver is manufacturing cholesterol from fragments
of carbohydrate, protein, and fat. In fact, the liver makes about 800 to 1500 mil-
ligrams of cholesterol per day, ◆ thus contributing much more to the body’s total
than does the diet.
Cholesterol’s harmful effects in the body occur when it forms deposits in the ar-
tery walls. These deposits lead to atherosclerosis, a disease that causes heart at-
tacks and strokes. (Chapter 27 provides many more details.)
Sterols have a multiple-ring structure that differs from the structure of other
lipids. In the body, sterols include cholesterol, bile, vitamin D, and some hor-
mones. Animal-derived foods contain cholesterol. To summarize, the mem-
bers of the lipid family include:
• Triglycerides (fats and oils), which are made of:
• Glycerol (1 per triglyceride) and
• Fatty acids (3 per triglyceride); depending on the number of double
bonds, fatty acids may be:
• Saturated (no double bonds)
• Monounsaturated (one double bond)
• Polyunsaturated (more than one double bond); depending on the loca-
tion of the double bonds, polyunsaturated fatty acids may be:
• Omega-3 (first double bond 3 carbons away from methyl end)
• Omega-6 (first double bond 6 carbons away from methyl end)
• Phospholipids (such as lecithin)
• Sterols (such as cholesterol)
IN SUMMARY
Digestion, Absorption, and Transport
of Lipids
Each day, the GI tract receives, on average from the food we eat, 50 to 100 grams of
triglycerides, 4 to 8 grams of phospholipids, and 200 to 350 milligrams of choles-
terol. The body faces a challenge in digesting and absorbing these lipids: getting at
them. Fats are hydrophobic—that is, they tend to separate from the watery fluids
of the GI tract—whereas the enzymes for digesting fats are hydrophilic. The chal-
lenge is keeping the fats mixed in the watery fluids of the GI tract.
Lipid Digestion
The goal of fat digestion is to dismantle triglycerides into small molecules that the
body can absorb and use—namely, monoglycerides, fatty acids, and glycerol. Fig-
ure 5-12 (p. 148) traces the digestion of triglycerides through the GI tract, and the fol-
lowing paragraphs provide the details.
In the Mouth Fat digestion starts off slowly in the mouth, with some hard fats be-
ginning to melt when they reach body temperature. A salivary gland at the base of
the tongue releases an enzyme (lingual lipase) ◆ that plays a minor role in fat
◆ Reminder: An enzyme that hydrolyzes lipids
is called a lipase; lingual refers to the tongue.
atherosclerosis (ATH-er-oh-scler-OH-sis): a
type of artery disease characterized by
placques (accumulations of lipid-containing
material) on the inner walls of the arteries
(see Chapter 27).
hydrophobic (high-dro-FOE-bick): a term
referring to water-fearing, or non-water-
soluble, substances; also known as lipophilic
(fat loving).
• hydro = water
• phobia = fear
• lipo = lipid
• phile = love
hydrophilic (high-dro-FIL-ick): a term referring
to water-loving, or water-soluble, substances.
monoglycerides: molecules of glycerol with
one fatty acid attached. A molecule of
glycerol with two fatty acids attached is a
diglyceride.
• mono = one
• di = two
CH2
CH3
H3C
CH3
CH3
HO
CH3
CH3
H3C CH3
CH3
Cholesterol
Vitamin D3
FIGURE 5-11 Cholesterol
The fat-soluble vitamin D is synthesized from
cholesterol; notice the many structural similar-
ities. The only difference is that cholesterol has
a closed ring (highlighted in red), whereas
vitamin D’s is open, accounting for its vitamin
activity. Notice, too, how different cholesterol
is from the triglycerides and phospholipids.
◆ Compounds made from cholestrol:
• Bile acids
• Steroid hormones (testosterone, andro-
gens, estrogens, progesterones, cortisol,
cortisone, and aldosterone)
• Vitamin D
◆ For perspective, the Daily Value for
cholesterol is 300 mg/day.

148 • CHAPTER 5
digestion in adults and an active role in infants. In infants, this enzyme efficiently
digests the short- and medium-chain fatty acids found in milk.
In the Stomach In a quiet stomach, fat would float as a layer above the other
components of swallowed food. But the strong muscle contractions of the stomach
propel the stomach contents toward the pyloric sphincter. Some chyme passes
Mouth and salivary glands
Stomach
Small intestine
Large intestine
Some fat and cholesterol, trapped in fiber, exit
in feces.
Some hard fats begin to melt as they reach
body temperature. The sublingual salivary gland
in the base of the tongue secretes lingual lipase.
The acid-stable lingual lipase initiates lipid
digestion by hydrolyzing one bond of
triglycerides to produce diglycerides and fatty
acids. The degree of hydrolysis by lingual
lipase is slight for most fats but may be
appreciable for milk fats. The stomach’s
churning action mixes fat with water and acid.
A gastric lipase accesses and hydrolyzes (only
a very small amount of) fat.
Bile flows in from the gallbladder (via the
common bile duct):
Pancreatic lipase flows in from the
pancreas (via the pancreatic duct):
Monoglycerides,
glycerol, fatty
acids (absorbed)
FAT
Salivary
glands
Mouth
Tongue
Sublingual
salivary
gland
Gallbladder
(Liver)
Stomach
Pancreatic
duct
Pancreas
Common
bile duct
Small
intestine
Large
intestine
Emulsified fat
(triglycerides)
Fat Emulsified fat
Bile
Pancreatic
(and intestinal)
lipase
FIGURE 5-12 Fat Digestion in the GI Tract

through the pyloric sphincter periodically, but the remaining partially digested food
is propelled back into the body of the stomach. This churning grinds the solid pieces
to finer particles, mixes the chyme, and disperses the fat into smaller droplets. These
actions help to expose the fat for attack by the gastric lipase enzyme—an enzyme
that performs best in the acidic environment of the stomach. Still, little fat digestion
takes place in the stomach; most of the action occurs in the small intestine.
In the Small Intestine When fat enters the small intestine, it triggers the re-
lease of the hormone cholecystokinin (CCK), which signals the gallbladder to
release its stores of bile. (Remember that the liver makes bile, and the gallblad-
der stores it until it is needed.) Among bile’s many ingredients ◆ are bile acids,
which are made in the liver from cholesterol and have a similar structure. In
addition, they often pair up with an amino acid (a building block of protein).
The amino acid end is attracted to water, and the sterol end is attracted to fat
(see Figure 5-13, p. 150). This structure improves bile’s ability to act as an emul-
sifier, drawing fat molecules into the surrounding watery fluids. There, the fats
are fully digested as they encounter lipase enzymes from the pancreas and
small intestine. The process of emulsification is diagrammed in Figure 5-14
(p. 150).
Most of the hydrolysis of triglycerides occurs in the small intestine. The major
fat-digesting enzymes are pancreatic lipases; some intestinal lipases are also active.
These enzymes remove one, then the other, of each triglyceride’s outer fatty acids,
leaving a monoglyceride. Occasionally, enzymes remove all three fatty acids, leav-
ing a free molecule of glycerol. Hydrolysis of a triglyceride is shown in Figure 5-15
(p. 151).
Phospholipids are digested similarly—that is, their fatty acids are removed by
hydrolysis. The two fatty acids and the remaining phospholipid fragment are then
absorbed. Most sterols can be absorbed as is; if any fatty acids are attached, they
are first hydrolyzed off.
Bile’s Routes After bile enters the small intestine and emulsifies fat, it has two pos-
sible destinations, illustrated in Figure 5-16 (p. 151). Most of the bile is reabsorbed
from the intestine and recycled. The other possibility is that some of the bile can be
trapped by dietary fibers in the large intestine and carried out of the body with the
feces. Because cholesterol is needed to make bile, the excretion of bile effectively re-
duces blood cholesterol. As Chapter 4 explains, the dietary fibers most effective at
lowering blood cholesterol this way are the soluble fibers commonly found in fruits,
whole grains, and legumes.
Lipid Absorption
Figure 5-17 (p. 152) illustrates the absorption of lipids. Small molecules of digested
triglycerides (glycerol and short- and medium-chain fatty acids) can diffuse easily
into the intestinal cells; they are absorbed directly into the bloodstream. Larger
molecules (the monoglycerides and long-chain fatty acids) merge into spherical
complexes, known as micelles. Micelles are emulsified fat droplets formed by mol-
ecules of bile surrounding monoglycerides and fatty acids. This configuration per-
mits solubility in the watery digestive fluids and transportation to the intestinal
cells. Upon arrival, the lipid contents of the micelles diffuse into the intestinal cells.
Once inside, the monoglycerides and long-chain fatty acids are reassembled into
new triglycerides.
Within the intestinal cells, the newly made triglycerides and other lipids (choles-
terol and phospholipids) are packed with protein into transport vehicles known as
chylomicrons. The intestinal cells then release the chylomicrons into the lym-
phatic system. The chylomicrons glide through the lymph until they reach a point
of entry into the bloodstream at the thoracic duct near the heart. (Recall from
Chapter 3 that nutrients from the GI tract that enter the lymph system bypass the
liver at first.) The blood carries these lipids to the rest of the body for immediate use
micelles (MY-cells): tiny spherical complexes
of emulsified fat that arise during digestion;
most contain bile salts and the products of
lipid digestion, including fatty acids,
monoglycerides, and cholesterol.
chylomicrons (kye-lo-MY-cronz): the class of
lipoproteins that transport lipids from the
intestinal cells to the rest of the body.
◆ In addition to bile acids and bile salts, bile
contains cholesterol, phospholipids
(especially lecithin), antibodies, water, elec-
trolytes, and bilirubin and biliverdin
(pigments resulting from the breakdown of
heme).

or storage. A look at these lipids in the body reveals the kinds of fat the diet has
been delivering.3 The fat stores and muscle cells of people who eat a diet rich in un-
saturated fats, for example, contain more unsaturated fats than those of people
who select a diet high in saturated fats.
H
HO
HO CH
Bile acid made from cholesterol (hydrophobic) Bound to an amino acid
from protein (hydrophilic)
CH2 CH2 CH2
C NH COOH
O
CH3
OH
FIGURE 5-13 A Bile Acid
This is one of several bile acids the liver makes from cholesterol. It is then bound
to an amino acid to improve its ability to form micelles, spherical complexes of
emulsified fat. Most bile acids occur as bile salts, usually in association with
sodium, but sometimes with potassium or calcium.
In the stomach, the fat and watery
GI juices tend to separate. The
enzymes in the GI juices can’t
get at the fat.
After emulsification, more fat is
exposed to the enzymes, making
fat digestion more efficient.
Enzyme
Emulsified
fat
Bile’s emulsifying action converts
large fat globules into small
droplets that repel each other.
Emulsified fat
Fat
Enzymes
Watery
GI juices
When fat enters the small intestine,
the gallbladder secretes bile. Bile
has an affinity for both fat and water,
so it can bring the fat into the water.
Fat
Bile
Emulsified
fat
FIGURE 5-14 Emulsification of Fat by Bile
Like bile, detergents are emulsifiers and work the same way, which is why they are effective in removing grease spots from clothes.
Molecule by molecule, the grease is dissolved out of the spot and suspended in the water, where it can be rinsed away.
150 • CHAPTER 5
The body makes special arrangements to digest and absorb lipids. It provides
the emulsifier bile to make them accessible to the fat-digesting lipases that dis-
mantle triglycerides, mostly to monoglycerides and fatty acids, for absorption
by the intestinal cells. The intestinal cells assemble freshly absorbed lipids into
chylomicrons, lipid packages with protein escorts, for transport so that cells all
over the body may select needed lipids from them.
IN SUMMARY
Lipid Transport
The chylomicrons are only one of several clusters of lipids and proteins that are used
as transport vehicles for fats. As a group, these vehicles are known as lipoproteins,
lipoproteins (LIP-oh-PRO-teenz): clusters of
lipids associated with proteins that serve as
transport vehicles for lipids in the lymph and
blood.

and they solve the body’s problem of transporting fat through the watery blood-
stream. The body makes four main types of lipoproteins, distinguished by their size
and density.* Each type contains different kinds and amounts of lipids and proteins.
◆ Figure 5-18 (p. 153) shows the relative compositions and sizes of the lipoproteins.
Chylomicrons The chylomicrons are the largest and least dense of the lipopro-
teins. They transport diet-derived lipids (mostly triglycerides) from the intestine (via
the lymph system) to the rest of the body. Cells all over the body remove triglycerides
from the chylomicrons as they pass by, so the chylomicrons get smaller and smaller.
Within 14 hours after absorption, most of the triglycerides have been depleted, and
only a few remnants of protein, cholesterol, and phospholipid remain. Special pro-
tein receptors on the membranes of the liver cells recognize and remove these chy-
lomicron remnants from the blood. After collecting the remnants, the liver cells first
dismantle them and then either use or recycle the pieces.
VLDL (Very-Low-Density Lipoproteins) Meanwhile, in the liver—the most ac-
tive site of lipid synthesis—cells are synthesizing other lipids. The liver cells use fatty
acids arriving in the blood to make cholesterol, other fatty acids, and other com-
pounds. At the same time, the liver cells may be making lipids from carbohydrates,
proteins, or alcohol. Ultimately, the lipids made in the liver and those collected from
chylomicron remnants are packaged with proteins as VLDL (very-low-density
lipoprotein) and shipped to other parts of the body.
As the VLDL travel through the body, cells remove triglycerides, causing the VLDL
to shrink. As a VLDL loses triglycerides, the proportion of lipids shifts, and the
lipoprotein density increases. The remaining cholesterol-rich lipoprotein eventually
becomes an LDL (low-density lipoprotein).† This transformation explains why
LDL contain few triglycerides but are loaded with cholesterol.
Triglyceride
Bonds break
The triglyceride and two molecules of water are split.
The H and OH from water complete the structures of
two fatty acids and leave a monoglyceride.
Monoglyceride + 2 fatty acids
These products may pass into the intestinal cells, but sometimes the
monoglyceride is split with another molecule of water to give a third
fatty acid and glycerol. Fatty acids, monoglycerides, and glycerol
are absorbed into intestinal cells.
Bonds break
H C O
H
H C O
H C O
H
C
O
C
O
H
C
H
H
H
C
H
H
C
O
H
C
H
H
H O H
H O H
C
C
O
H
C
H
H
H C O
H
H C O
H C O
H
H
H
H
C
H
H
H O
C
O
H
C
H
H
H O
O
FIGURE 5-15 Digestion (Hydrolysis) of a Triglyceride
In the gallbladder,
bile is stored.
In the small intestine,
bile emulsifies fats.
In the colon, bile that has
been trapped by soluble
fibers is lost in feces.
In the liver,
bile is
made from
cholesterol.
Bile reabsorbed
into the blood
FIGURE 5-16 Enterohepatic Circulation
Most of the bile released into the small
intestine is reabsorbed and sent back to
the liver to be reused. This cycle is
called the enterohepatic circulation of
bile. Some bile is excreted.
• enteron intestine
• hepat liver
* Chemists can identify the various lipoproteins by their density. They place a blood sample below a
thick fluid in a test tube and spin the tube in a centrifuge. The most buoyant particles (highest in
lipids) rise to the top and have the lowest density; the densest particles (highest in proteins) remain at
the bottom and have the highest density. Others distribute themselves in between.
† Before becoming LDL, the VLDL are first transformed into intermediate-density lipoproteins (IDL),
sometimes called VLDL remnants. Some IDL may be picked up by the liver and rapidly broken down;
those IDL that remain in circulation continue to deliver triglycerides to the cells and eventually become
LDL. Researchers debate whether IDL are simply transitional particles or a separate class of lipoproteins;
normally, IDL do not accumulate in the blood. Measures of blood lipids include IDL with LDL.
VLDL (very-low-density lipoprotein): the
type of lipoprotein made primarily by liver
cells to transport lipids to various tissues in the
body; composed primarily of triglycerides.
LDL (low-density lipoprotein): the type of
lipoprotein derived from very-low-density
lipoproteins (VLDL) as VLDL triglycerides are
removed and broken down; composed
primarily of cholesterol.
◆ The more lipids, the lower the density; the
more proteins, the higher the density.

LDL (Low-Density Lipoproteins)
The LDL circulate throughout the
body, making their contents avail-
able to the cells of all tissues—
muscles (including the heart
muscle), fat stores, the mammary
glands, and others. The cells take
triglycerides, cholesterol, and
phospholipids to build new mem-
branes, make hormones or other
compounds, or store for later use.
Special LDL receptors on the liver
cells play a crucial role in the con-
trol of blood cholesterol concen-
trations by removing LDL from
circulation.
HDL (High-Density Lipopro-
teins) Fat cells may release glyc-
erol, fatty acids, cholesterol, and
phospholipids to the blood. The
liver makes HDL (high-density
lipoprotein) to carry cholesterol
from the cells back to the liver for
recycling or disposal.
Health Implications The distinc-
tion between LDL and HDL has im-
plications for the health of the heart
and blood vessels. The blood choles-
terol linked to heart disease is LDL
cholesterol. HDL also carry choles-
terol, but elevated HDL represent
cholesterol returning ◆ from the
rest of the body to the liver for
breakdown and excretion. High
LDL cholesterol is associated with a
high risk of heart attack, whereas
high HDL cholesterol seems to
have a protective effect. This is why
some people refer to LDL as “bad,” and HDL as “good,” cholesterol. ◆ Keep in
mind that the cholesterol itself is the same, and that the differences between LDL
and HDL reflect the proportions and types of lipids and proteins within them—not
the type of cholesterol. The margin ◆ lists factors that influence LDL and HDL,
and Chapter 27 provides many more details.
Not too surprisingly, numerous genes influence how the body handles the up-
take, synthesis, transport, and degradation of the lipoproteins. Much current re-
search is focused on how nutrient-gene interactions may direct the progression of
heart disease.
Via lymph to blood
Large lipids such as
monoglycerides and long-chain
fatty acids combine with bile,
forming micelles that are
sufficiently water soluble to
penetrate the watery solution that
bathes the absorptive cells.
There the lipid contents of the
micelles diffuse into the cells.
Glycerol and small lipids such as short- and medium-chain
fatty acids can move directly into the bloodstream.
Short-chain
fatty acids Medium-chain
fatty acids
Glycerol
Chylomicrons
Lacteal
(lymph)
Capillary
network
Blood vessels
Via blood to liver
Long-
chain
fatty
acids
Micelle
Monoglyceride
Chylomicron
Triglyceride
Protein
Small intestine
Stomach
FIGURE 5-17 Animated! Absorption of Fat
The end products of fat digestion are mostly monoglycerides, some fatty acids, and very
little glycerol. Their absorption differs depending on their size. (In reality, molecules of
fatty acid are too small to see without a powerful microscope, whereas villi are visible to
the naked eye.)
152 • CHAPTER 5
◆ The transport of cholesterol from the tissues
to the liver is sometimes called the scavenger
pathway.
◆ To help you remember, think of elevated
HDL as Healthy and elevated LDL as Less
healthy.
◆ Factors that lower LDL or raise HDL:
• Weight control
• Monounsaturated or polyunsaturated,
instead of saturated, fat in the diet
• Soluble, viscous fibers (see Chapter 4)
• Phytochemicals (see Highlight 13)
• Moderate alcohol consumption
• Physical activity
The liver assembles lipids and proteins into lipoproteins for transport around
the body. All four types of lipoproteins carry all classes of lipids (triglycerides,
phospholipids, and cholesterol), but the chylomicrons are the largest and the
highest in triglycerides; VLDL are smaller and are about half triglycerides; LDL
are smaller still and are high in cholesterol; and HDL are the smallest and are
rich in protein.
IN SUMMARY
HDL (high-density lipoprotein): the type
of lipoprotein that transports cholesterol
back to the liver from the cells; composed
primarily of protein.

100
80
60
40
20
0
Percent Protein
Cholesterol
Phospholipid
Triglyceride
Chylomicron
Phospholipid
Cholesterol
Triglyceride
Chylomicron
VLDL
HDL
A typical lipoprotein contains an
interior of triglycerides and
cholesterol surrounded by
phospholipids. The phospholipids’
fatty acid “tails” point towards the
interior, where the lipids are.
Proteins near the outer ends of the
phospholipids cover the structure.
This arrangement of hydrophobic
molecules on the inside and
hydrophilic molecules on the
outside allows lipids to travel
through the watery fluids of the
blood.
This solar system of lipoproteins shows their relative
sizes. Notice how large the fat-filled chylomicron is
compared with the others and how the others get
progressively smaller as their proportion of fat declines
and protein increases.
Chylomicrons contain so little protein and so much triglyceride
that they are the lowest in density.
Very-low-density lipoproteins (VLDL) are half triglycerides,
accounting for their very low density.
Low-density lipoproteins (LDL) are half cholesterol, accounting
for their implication in heart disease.
High-density lipoproteins (HDL) are half protein, accounting
for their high density.
Protein
HDL
VLDL LDL
LDL
FIGURE 5-18 Sizes and Compositions of the Lipoproteins
Lipids in the Body
The blood carries lipids to various sites around the body. Once lipids arrive at their
destinations, they can get to work providing energy, insulating against temperature
extremes, protecting against shock, and maintaining cell membranes. This section
provides an overview of the roles of triglycerides and fatty acids and then of the
metabolic pathways they can follow within the body’s cells.
Roles of Triglycerides
First and foremost, the triglycerides—either from food or from the body’s fat stores—
provide the body with energy. When a person dances all night, her dinner’s triglyc-
erides provide some of the fuel that keeps her moving. When a person loses his
appetite, his stored triglycerides fuel much of his body’s work until he can eat again.
Efficient energy metabolism depends on the energy nutrients—carbohydrate,
fat, and protein—supporting each other. Glucose fragments combine with fat
fragments during energy metabolism, and fat and carbohydrate help spare pro-
tein, providing energy so that protein can be used for other important tasks.

154 • CHAPTER 5
Fat also insulates the body. Fat is a poor conductor of heat, so the layer of fat be-
neath the skin helps keep the body warm. Fat pads also serve as natural shock ab-
sorbers, providing a cushion for the bones and vital organs.
Essential Fatty Acids
The human body needs fatty acids, and it can make all but two of them—linoleic
acid (the 18-carbon omega-6 fatty acid) and linolenic acid (the 18-carbon omega-3
fatty acid). These two fatty acids must be supplied by the diet and are therefore es-
sential fatty acids. A simple definition of an essential nutrient has already been
given: a nutrient that the body cannot make, or cannot make in sufficient quanti-
ties to meet its physiological needs. The cells do not possess the enzymes to make
any of the omega-6 or omega-3 fatty acids from scratch, nor can they convert an
omega-6 fatty acid to an omega-3 fatty acid or vice versa. Cells can, however, start
with the 18-carbon member of an omega family and make the longer fatty acids of
that family by forming double bonds (desaturation) and lengthening the chain two
carbons at a time (elongation), as shown in Figure 5-19. This is a slow process be-
cause the omega-3 and omega-6 families compete for the same enzymes. Too much
of a fatty acid from one family can create a deficiency of the other family’s longer
fatty acids, which is critical only when the diet fails to deliver adequate supplies.
Therefore, the most effective way to maintain body supplies of all the omega-6 and
omega-3 fatty acids is to obtain them directly from foods—most notably, from veg-
etable oils, seeds, nuts, fish, and other marine foods.
Linoleic Acid and the Omega-6 Family Linoleic acid is the primary member
of the omega-6 family. When the body receives linoleic acid from the diet, it can
make other members of the omega-6 family—such as the 20-carbon polyunsatu-
rated fatty acid, arachidonic acid. If a linoleic acid deficiency should develop,
arachidonic acid, and all other fatty acids that derive from linoleic acid, would also
become essential and have to be obtained from the diet. ◆ Normally, vegetable oils
and meats supply enough omega-6 fatty acids to meet the body’s needs.
Linolenic Acid and the Omega-3 Family Linolenic acid is the primary mem-
ber of the omega-3 family.* Like linoleic acid, linolenic acid cannot be made in the
body and must be supplied by foods. Given this 18-carbon fatty acid, the body can
make small amounts of the 20- and 22-carbon members of the omega-3 series,
eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA). These
omega-3 fatty acids are essential for normal growth and development, especially in
the eyes and brain.4 They may also play an important role in the prevention and
treatment of heart disease.
Eicosanoids The body uses arachidonic acid and EPA to make substances known
as eicosanoids. Eicosanoids are a diverse group of compounds that are sometimes
described as “hormonelike,” but they differ from hormones in important ways. For
one, hormones are secreted in one location and travel to affect cells all over the
body, whereas eicosanoids appear to affect only the cells in which they are made or
nearby cells in the same localized environment. For another, hormones elicit the
same response from all their target cells, whereas eicosanoids often have different ef-
fects on different cells.
The actions of various eicosanoids sometimes oppose each other. For example,
one causes muscles to relax and blood vessels to dilate, whereas another causes
muscles to contract and blood vessels to constrict. Certain eicosanoids participate
in the immune response to injury and infection, producing fever, inflammation,
and pain. One of the ways aspirin relieves these symptoms is by slowing the syn-
thesis of these eicosanoids.
Linoleic acid (18:2)
desaturation
(18:3)
elongation
(20:3)
desaturation
Arachidonic acid (20:4)
The first number indicates the number
of carbons and the second, the number
of double bonds. Similar reactions
occur when the body makes the
omega-3 fatty acids EPA and DHA from
linolenic acid.
FIGURE 5-19 The Pathway from One
Omega-6 Fatty Acid to Another
◆ A nonessential nutrient (such as arachidonic
acid) that must be supplied by the diet in
special circumstances (as in a linoleic acid
deficiency) is considered conditionally
essential.
* This omega-3 linolenic acid is known as alpha-linolenic acid and is the fatty acid referred to in this
chapter. Another fatty acid, also with 18 carbons and three double bonds, belongs to the omega-6 fam-
ily and is known as gamma-linolenic acid.
essential fatty acids: fatty acids needed by
the body but not made by it in amounts
sufficient to meet physiological needs.
arachidonic (a-RACK-ih-DON-ic) acid: an
omega-6 polyunsaturated fatty acid with 20
carbons and four double bonds; present in
small amounts in meat and other animal
products and synthesized in the body from
linoleic acid.
eicosapentaenoic (EYE-cossa-PENTA-ee-NO-
ick) acid (EPA): an omega-3
polyunsaturated fatty acid with 20 carbons
and five double bonds; present in fish and
synthesized in limited amounts in the body
from linolenic acid.
docosahexaenoic (DOE-cossa-HEXA-ee-NO-
ick) acid (DHA): an omega-3
polyunsaturated fatty acid with 22 carbons
and six double bonds; present in fish and
synthesized in limited amounts in the body
from linolenic acid.
eicosanoids (eye-COSS-uh-noyds):
derivatives of 20-carbon fatty acids;
biologically active compounds that help to
regulate blood pressure, blood clotting,
and other body functions. They include
prostaglandins (PROS-tah-GLAND-ins),
thromboxanes (throm-BOX-ains), and
leukotrienes (LOO-ko-TRY-eens).

Eicosanoids that derive from EPA differ from those that derive from arachidonic
acid, with those from EPA providing greater health benefits.5 The EPA eicosanoids
help lower blood pressure, prevent blood clot formation, protect against irregular
heartbeats, and reduce inflammation. Because the omega-6 and omega-3 fatty
acids compete for the same enzymes to make arachidonic acid and EPA and to
make the eicosanoids, the body needs these long-chain polyunsaturated fatty acids
from the diet to make eicosanoids in sufficient quantities.6
Fatty Acid Deficiencies Most diets in the United States and Canada meet the
minimum essential fatty acid requirement adequately. Historically, deficiencies
have developed only in infants and young children who have been fed fat-free milk
and low-fat diets or in hospital clients who have been mistakenly fed formulas that
provided no polyunsaturated fatty acids for long periods of time. Classic deficiency
symptoms include growth retardation, reproductive failure, skin lesions, kidney and
liver disorders, and subtle neurological and visual problems.
Interestingly, a deficiency of omega-3 fatty acids (EPA and DHA) may be associ-
ated with depression.7 Some neurochemical pathways in the brain become more ac-
tive and others become less active.8 It is unclear, however, which comes first—whether
inadequate intake alters brain activity or depression alters fatty acid metabolism. To
find the answers, researchers must untangle a multitude of confounding factors. Double thanks: The body’s fat stores provide
energy for a walk, and the heel’s fat pads cush-
ion against the hard pavement.
Newly imported triglycerides first form
small droplets at the periphery of the
cell, then merge with the large, central
globule.
As the central globule enlarges, the fat
cell membrane expands to accommodate
its swollen contents.
Large central globule
of (pure) fat
Cell nucleus
Cytoplasm
FIGURE 5-20 An Adipose Cell
◆ Reminder: Gram for gram, fat provides more
than twice as much energy (9 kcal) as carbo-
hydrate or protein (4 kcal).
In the body, triglycerides:
• Provide an energy reserve when stored in the body’s fat tissue
• Insulate against temperature extremes
• Protect against shock
• Help the body use carbohydrate and protein efficiently
Linoleic acid (18 carbons, omega-6) and linolenic acid (18 carbons, omega-3)
are essential nutrients. They serve as structural parts of cell membranes and as
precursors to the longer fatty acids that can make eicosanoids—powerful com-
pounds that participate in blood pressure regulation, blood clot formation,
and the immune response to injury and infection, among other functions. Be-
cause essential fatty acids are common in the diet and stored in the body, de-
ficiencies are unlikely.
IN SUMMARY
A Preview of Lipid Metabolism
The blood delivers triglycerides to the cells for their use. This is a preview of how the
cells store and release energy from fat; Chapter 7 provides details.
Storing Fat as Fat The triglycerides, familiar as the fat in foods and as body fat,
serve the body primarily as a source of fuel. Fat provides more than twice the energy
of carbohydrate and protein, ◆ making it an extremely efficient storage form of en-
ergy. Unlike the liver’s glycogen stores, the body’s fat stores have virtually unlimited
capacity, thanks to the special cells of the adipose tissue. Unlike most body cells,
which can store only limited amounts of fat, the fat cells of the adipose tissue read-
ily take up and store fat. An adipose cell is depicted in Figure 5-20.
To convert food fats to body fat, the body simply breaks them down, absorbs the
parts, and puts them (and others) together again in storage. It requires very little
energy to do this. An enzyme—lipoprotein lipase (LPL)—hydrolyzes triglyc-
erides from lipoproteins, producing glycerol, fatty acids, and monoglycerides that
enter the adipose cells. Inside the cells, other enzymes reassemble the pieces into
triglycerides again for storage. Earlier, Figure 5-4 (p. 143) showed how the body can
make a triglyceride from glycerol and fatty acids. Triglycerides fill the adipose cells,
storing a lot of energy in a relatively small space. Adipose cells store fat
adipose (ADD-ih-poce) tissue: the body’s fat
tissue; consists of masses of triglyceride-
storing cells.
lipoprotein lipase (LPL): an enzyme that
hydrolyzes triglycerides passing by in the
bloodstream and directs their parts into the
cells, where they can be metabolized for
energy or reassembled for storage.
©
Jim
Cummins/Taxi/Getty
Images

156 • CHAPTER 5
after meals when a heavy traffic of chylomicrons and VLDL loaded with triglyc-
erides passes by; they release it later whenever the other cells need replenishing.
Using Fat for Energy Fat supplies 60 percent of the body’s ongoing energy needs
during rest. During prolonged light to moderately intense exercise or extended peri-
ods of food deprivation, fat stores may make a slightly greater contribution to en-
ergy needs.
When cells demand energy, an enzyme (hormone-sensitive lipase) inside
the adipose cells responds by dismantling stored triglycerides and releasing the
glycerol and fatty acids directly into the blood. Energy-hungry cells anywhere in
the body can then capture these compounds and take them through a series of
chemical reactions to yield energy, carbon dioxide, and water.
A person who fasts (drinking only water) will rapidly metabolize body fat. A
pound of body fat provides 3500 kcalories, ◆ so you might think a fasting person
who expends 2000 kcalories a day could lose more than half a pound of body fat
each day.* Actually, the person has to obtain some energy from lean tissue because
the brain, nerves, and red blood cells need glucose. Also, the complete breakdown
of fat requires carbohydrate or protein. Even on a total fast, a person cannot lose
more than half a pound of pure fat per day. Still, in conditions of enforced starva-
tion—say, during a siege or a famine—a fatter person can survive longer than a
thinner person thanks to this energy reserve.
Although fat provides energy during a fast, it can provide very little glucose to
give energy to the brain and nerves. Only the small glycerol molecule can be con-
verted to glucose; fatty acids cannot be. (Figure 7-12 on p. 224 illustrates how only
3 of the 50 or so carbon atoms in a molecule of fat can yield glucose.) After pro-
longed glucose deprivation, brain and nerve cells develop the ability to derive
about two-thirds of their minimum energy needs from the ketone bodies that the
body makes from fat fragments. Ketone bodies cannot sustain life by themselves,
however. As Chapter 7 explains, fasting for too long will cause death, even if the
person still has ample body fat.
Fat supplies most of the energy during a long-
distance run.
◆ 1 lb body fat = 3500 kcal
The body can easily store unlimited amounts of fat if given excesses, and this
body fat is used for energy when needed. (Remember that the liver can also
convert excess carbohydrate and protein into fat.) Fat breakdown requires si-
multaneous carbohydrate breakdown for maximum efficiency; without carbo-
hydrate, fats break down to ketone bodies.
IN SUMMARY
Intakes of Lipids
Of all the nutrients, fat is most often linked with heart disease, some types of cancer,
and obesity. Fortunately, the same recommendation can help with all of these
health problems: choose a diet that is low in saturated fats, trans fats, and cholesterol
and moderate in total fat.
Health Effects of Lipids
Hearing a physician say, “Your blood lipid profile looks fine,” is reassuring. The
blood lipid profile ◆ reveals the concentrations of various lipids in the blood,
◆ Desirable blood lipid profile:
• Total cholesterol: 200 mg/dL
• LDL cholesterol: 100 mg/dL
• HDL cholesterol: 60 mg/dL
• Triglycerides: 150 mg/dL
* The reader who knows that 1 pound = 454 grams and that 1 gram of fat = 9 kcalories may wonder
why a pound of body fat does not equal 4086 (9 454) kcalories. The reason is that body fat contains
some cell water and other materials; it is not quite pure fat.
hormone-sensitive lipase: an enzyme inside
adipose cells that responds to the body’s need
for fuel by hydrolyzing triglycerides so that
their parts (glycerol and fatty acids) escape
into the general circulation and thus become
available to other cells for fuel. The signals
to which this enzyme responds include
epinephrine and glucagon, which oppose
insulin (see Chapter 4).
blood lipid profile: results of blood tests
that reveal a person’s total cholesterol,
triglycerides, and various lipoproteins.
©
Bob
Thomas/Stone/Getty
Images

notably triglycerides and cholesterol, and their lipoprotein carriers (VLDL, LDL, and
HDL). This information alerts people to possible disease risks and perhaps to a need
for changing their exercise and eating habits. Both the amounts and types of fat in
the diet influence people’s risk for disease.9
Heart Disease Most people realize that elevated blood cholesterol is a major risk
factor for cardiovascular disease. Cholesterol accumulates in the arteries, re-
stricting blood flow and raising blood pressure. The consequences are deadly; in fact,
heart disease is the nation’s number one killer of adults. Blood cholesterol level is of-
ten used to predict the likelihood of a person’s suffering a heart attack or stroke; the
higher the cholesterol, the earlier and more likely the tragedy. Much of the effort to
prevent heart disease focuses on lowering blood cholesterol.
Commercials advertise products that are low in cholesterol, and magazine arti-
cles tell readers how to cut the cholesterol from their favorite recipes. What most
people don’t realize, though, is that food cholesterol does not raise blood cholesterol
as dramatically as saturated fat does.
Risks from Saturated Fats As mentioned earlier, LDL cholesterol raises the risk
of heart disease. Saturated fats are most often implicated in raising LDL cholesterol.
In general, the more saturated fat in the diet, the more LDL cholesterol in the body.
Not all saturated fats have the same cholesterol-raising effect, however. Most no-
table among the saturated fatty acids that raise blood cholesterol are lauric, myris-
tic, and palmitic acids (12, 14, and 16 carbons, respectively). In contrast, stearic acid
(18 carbons) does not seem to raise blood cholesterol. However, making such distinc-
tions may be impractical in diet planning because these saturated fatty acids typi-
cally appear together in the same foods.
Fats from animal sources are the main sources of saturated fats ◆ in most peo-
ple’s diets (see Figure 5-21). Some vegetable fats (coconut and palm) and hydro-
genated fats provide smaller amounts of saturated fats. Selecting poultry or fish
and fat-free milk products helps to lower saturated fat intake and heart disease risk.
Using nonhydrogenated margarine and unsaturated cooking oil is another simple
change that can dramatically lower saturated fat intake.
Risks from Trans Fats Research also suggests an association between dietary
trans-fatty acids and heart disease.10 In the body, trans-fatty acids alter blood choles-
terol the same way some saturated fats do: they raise LDL cholesterol and, at high
intakes, lower HDL cholesterol.11 Trans-fatty acids also appear to increase inflamma-
tion and insulin resistance.12 Limiting the intake of trans-fatty acids can improve
blood cholesterol and lower the risk of heart disease. The estimated average intake
of trans-fatty acids in the United States is about 5 grams per day—mostly from prod-
ucts that have been hydrogenated.13 ◆
Reports on trans-fatty acids have raised consumer doubts about whether mar-
garine is, after all, a better choice than butter for heart health. The American Heart
Association has stated that because butter is rich in both saturated fat and choles-
terol whereas margarine is made from vegetable fat with no dietary cholesterol,
margarine is still preferable to butter. Be aware that soft margarines (liquid or tub)
◆ are less hydrogenated and relatively lower in trans-fatty acids; consequently, they
do not raise blood cholesterol as much as the saturated fats of butter or the trans
fats of hard (stick) margarines do. Some manufacturers are now offering nonhydro-
genated margarines that are “trans fat free.” The last section of this chapter de-
scribes how to read food labels and compares butter and margarines. Whichever
you decide to use, remember to use them sparingly.
Risks from Cholesterol Although its effect is not as strong as that of saturated fat
or trans fat, dietary cholesterol also raises blood cholesterol and increases the risk of
heart disease. To maximize the effect on blood cholesterol, limit dietary cholesterol
as well.
Recall that cholesterol is found in all foods derived from animals. Consequently,
eating less fat from meats, eggs, and milk products helps lower dietary cholesterol in-
take ◆ (as well as total and saturated fat intakes). Figure 5-22 (p. 158) shows the
◆ Major sources of saturated fats:
• Whole milk, cream, butter, cheese
• Fatty cuts of beef and pork
• Coconut, palm, and palm kernel oils
(and products containing them such as
candies, pastries, pies, doughnuts, and
cookies)
◆ Major sources of trans fats:
• Deep-fried foods (vegetable shortening)
• Cakes, cookies, doughnuts, pastry,
crackers
• Snack chips
• Margarine
• Imitation cheese
• Meat and dairy products
◆ When selecting margarine, look for:
• Soft (liquid or tub) instead of hard (stick)
• 2 g saturated fat
• Liquid vegetable oil (not hydrogenated or
partially hydrogenated) as first ingredient
• “Trans fat free”
◆ Major sources of cholesterol:
• Eggs
• Milk products
• Meat, poultry, shellfish
Milk, yogurt, and
cheese 20%
Other 2% Eggs 2%
Nuts and
legumes
2%
Meat, poultry,
and fish 40%
Added fats
and oils 34%
Note that fruits, grains, and vegetables are
insignificant sources, unless saturated fats are
intentionally added to them during preparation.
FIGURE 5-21 Saturated Fats in the
U.S. Diet
cardiovascular disease (CVD): a general
term for all diseases of the heart and blood
vessels. Atherosclerosis is the main cause of
CVD. When the arteries that carry blood to
the heart muscle become blocked, the heart
suffers damage known as coronary heart
disease (CHD).
• cardio = heart
• vascular = blood vessels

158 • CHAPTER 5
cholesterol contents of selected foods. Many more foods, with their cholesterol con-
tents, appear in Appendix H. For most people trying to lower blood cholesterol,
however, limiting saturated fat is more effective than limiting cholesterol intake.
Most foods that are high in cholesterol are also high in saturated fat, but eggs
are an exception. An egg contains only 1 gram of saturated fat but just over 200
milligrams of cholesterol—roughly two-thirds of the recommended daily limit. For
people with a healthy lipid profile, eating one egg a day is not detrimental. People
with high blood cholesterol, however, may benefit from limiting daily cholesterol
intake to less that 200 milligrams.14 When eggs are included in the diet, other
sources of cholesterol may need to be limited on that day. Eggs are a valuable part
of the diet because they are inexpensive, useful in cooking, and a source of high-
quality protein and other nutrients. Low saturated fat, high omega-3 fat eggs are
now available, and food manufacturers have produced several fat-free, cholesterol-
free egg substitutes.
Benefits from Monounsaturated Fats and Polyunsaturated Fats Replac-
ing both saturated and trans fats with monounsaturated ◆ and polyunsaturated ◆
fats may be the most effective dietary strategy in preventing heart disease. The lower
rate of heart disease among people in the Mediterranean region of the world is of-
ten attributed to their liberal use of olive oil, a rich source of monounsaturated fatty
acids. Olive oil also delivers valuable phytochemicals that help to protect against
heart disease.15 Replacing saturated fats with the polyunsaturated fatty acids of
other vegetable oils also lowers blood cholesterol.16 Highlight 5 examines various
types of fats and their roles in supporting or harming heart health.
Benefits from Omega-3 Fats Research on the different types of fats has spot-
lighted the beneficial effects of the omega-3 ◆ polyunsaturated fatty acids in reduc-
ing the risks of heart disease and stroke.17 Regular consumption of omega-3 fatty
acids helps to prevent blood clots, protect against irregular heartbeats, and lower
blood pressure, especially in people with hypertension or atherosclerosis.18
Milk
0 60 120 180
Milligrams
240 300
Milk
Yogurt, plain
Yogurt, plain
Cheddar cheese
Cottage cheese
Swiss cheese
Ice cream
Butter
Shrimp
Ground beef, lean
Chicken breast
Cod
Ham, lean
Sirloin steak, lean
Tuna, canned in water
Bologna, beef
Egg
1 c whole (150 kcal)
Food Serving size (kcalories)
1 c reduced-fat 2% (121 kcal)
1 c whole (150 kcal)
1 c low-fat (155 kcal)
11
⁄2
oz (170 kcal)
1
⁄2
c reduced-fat 2% (101 kcal)
11
⁄2
oz (140 kcal)
1
⁄2
c, 10% fat (133 kcal)
1 tsp (36 kcal)
3 oz boiled (85 kcal)
3 oz broiled (237 kcal)
3 oz roasted (141 kcal)
3 oz poached (88 kcal)
3 oz roasted (123 kcal)
3 oz broiled (171 kcal)
3 oz (99 kcal)
2 slices (144 kcal)
1 hard cooked (77 kcal)
CHOLESTEROL
Only foods of animal origin contain significant
cholesterol. Consequently, grains, vegetables,
legumes, and fruits provide virtually no
cholesterol.
Milk and milk products
Meats
Miscellaneous
Key:
Daily
Value
FIGURE 5-22 Cholesterol in Selected Foods
◆ Sources of monounsaturated fats:
• Olive oil, canola oil, peanut oil
• Avocados
◆ Sources of polyunsaturated fats:
• Vegetable oils (safflower, sesame, soy,
corn, sunflower)
• Nuts and seeds
◆ Major sources of omega-3 fats:
• Vegetable oils (canola, soybean, flaxseed)
• Walnuts, flaxseeds
• Fatty fish (mackerel, salmon, sardines)

Fatty fish are among the best sources of omega-3 fatty acids, and Highlight 5
features their role in supporting heart health. To maximize the benefits and mini-
mize the risks, ◆ most healthy people should eat two servings of fish a week.19
Balance Omega-6 and Omega-3 Intakes Table 5-2 provides sources of
omega-6 and omega-3 fatty acids. To obtain sufficient intakes and the right balance
between omega-6 and omega-3 fatty acids, ◆ most people need to eat more fish and
less meat.20 The American Heart Association recommends two servings of fish a
week, with an emphasis on fatty fish (salmon, herring, and mackerel, for exam-
ple).21 Eating fish instead of meat supports heart health, especially when combined
with physical activity. Even one fish meal a month may be enough to make a differ-
ence.22 When preparing fish, grill, bake, or broil, but do not fry. Fried fish from fast-
food restaurants and frozen fried fish products are often low in omega-3 fatty acids
and high in trans- and saturated fatty acids. Fish provides many minerals (except
iron) and vitamins and is leaner than most other animal-protein sources. When
used in a weight-loss program, eating fish improves blood lipids even more effec-
tively than can be explained by losing weight or eating fish alone.
In addition to fish, other functional foods ◆ are being developed to help con-
sumers improve their omega-3 fatty acid intake. For example, hens fed flaxseed
produce eggs rich in omega-3 fatty acids. Including even one enriched egg in the
diet daily can significantly increase a person’s intake of omega-3 fatty acids. An-
other option may be to select wild game or pasture-fed cattle, which provide more
omega-3 fatty acids and less saturated fat than grain-fed cattle.23
Omega-3 fatty acids are also available in capsules of fish oil supplements. Rou-
tine supplementation, however, is not recommended. High intakes of omega-3
polyunsaturated fatty acids may increase bleeding time, interfere with wound
healing, raise LDL cholesterol, and suppress immune function.*24 Such findings re-
inforce the concept that too much of a good thing can sometimes be harmful. Peo-
ple with heart disease, however, may benefit from doses greater than can be
achieved through diet alone. They should always consult a physician first because
including supplements as part of a treatment plan may be contraindicated for
some patients.25 Supplements may also provide relief for people with rheumatoid
arthritis or asthma.26
Cancer The evidence for links between dietary fats and cancer ◆ is less convincing
than for heart disease, but it does suggest possible associations between some types
◆ Fish relatively high in mercury:
• Tilefish (also called golden snapper or
golden bass), swordfish, king mackerel,
shark
Fish relatively low in mercury:
• Cod, haddock, pollock, salmon, sole,
tilapia
• Most shellfish
◆ Recommended omega-6 to omega-3 ratio:
6 to 1
TABLE 5-2 Sources of Omega-3 and Omega-6 Fatty Acids
Omega-6
Linoleic acid Vegetable oils (corn, sunflower, safflower, soybean, cottonseed), poultry fat,
nuts, seeds
Arachidonic acid Meats, poultry, eggs (or can be made from linoleic acid)
Omega-3
Linolenic acid Oils (flaxseed, canola, walnut, wheat germ, soybean)
Nuts and seeds (butternuts, flaxseeds, walnuts, soybean kernels)
Vegetables (soybeans)
EPA and DHA Human milk
Pacific oysters and fisha (mackerel, salmon, bluefish, mullet, sablefish,
menhaden, anchovy, herring, lake trout, sardines, tuna)
(or can be made from linolenic acid)
aAll fish contain some EPA and DHA; the amounts vary among species and within a species depending on such factors as diet,
season, and environment. The fish listed here, except tuna, provide at least 1 gram of omega-3 fatty acids in 100 grams of fish (3.5
ounces). Tuna provides fewer omega-3 fatty acids, but because it is commonly consumed, its contribution can be significant.
◆ Reminder: Functional foods contain
physiologically active compounds that pro-
vide health benefits beyond basic nutrition
(see Highlight 13 for a full discussion).
◆ Other risk factors for cancer include
smoking, alcohol, and environmental
contaminants. Chapter 29 provides more
details about these risk factors and the
development of cancer.
* Suppressed immune function is seen with daily intake of 0.9 to 9.4 grams EPA and 0.6 to 6.0 grams
DHA for 3 to 24 weeks.

160 • CHAPTER 5
of fat and some types of cancers.27 Dietary fat does not seem to initiate cancer devel-
opment but, instead, may promote cancer once it has arisen.
The relationship between dietary fat and the risk of cancer differs for various types
of cancers. In the case of breast cancer, evidence has been weak and inconclusive.
Some studies indicate little or no association between dietary fat and breast cancer;
others find that total energy intake and obesity contribute to the risk.28 In the case
of prostate cancer, some studies indicate a harmful association with total and sat-
urated fat, although a specific type fatty acid has not yet been implicated.29
The relationship between dietary fat and the risk of cancer differs for various
types of fats as well. The association between cancer and fat appears to be due pri-
marily to saturated fats or dietary fat from meats (which is mostly saturated). Fat
from milk or fish has not been implicated in cancer risk.30 In fact, the omega-3
fatty acids of fish may protect against some cancers, although evidence does not
support supplementation.31 Thus dietary advice to reduce cancer risks parallels
that given to reduce heart disease risks: reduce saturated fats and increase omega-
3 fatty acids.
Obesity Fat contributes more than twice as many kcalories ◆ per gram as either
carbohydrate or protein. Consequently, people who eat high-fat diets regularly may
exceed their energy needs and gain weight, especially if they are inactive.32 Because
fat boosts energy intake, cutting fat from the diet can be an effective strategy in cut-
ting kcalories. In some cases, though, choosing a fat-free food offers no kcalorie sav-
ings. Fat-free frozen desserts, for example, often have so much sugar added that the
kcalorie count can be as high as in the regular-fat product. In this case, therefore,
cutting fat and adding carbohydrate offers no kcalorie savings or weight-loss advan-
tage. In fact, it may even raise energy intake and exacerbate weight problems. Later
chapters revisit the role of dietary fat in the development of obesity.
◆ Fat is a more concentrated energy source
than the other energy nutrients: 1 g carbo-
hydrate or protein = 4 kcal, but 1 g fat =
9 kcal
High blood LDL cholesterol poses a risk of heart disease, and high intakes of
saturated and trans fats, specifically, contribute most to high LDL. Cholesterol
in foods presents less of a risk. Omega-3 fatty acids appear to be protective.
IN SUMMARY
Recommended Intakes of Fat
Some fat in the diet is essential for good health, but too much fat, especially satu-
rated fat, increases the risks for chronic diseases. Defining the exact amount of fat,
saturated fat, or cholesterol that benefits health or begins to harm health, however,
is not possible. For this reason, no RDA or upper limit has been set. Instead, the DRI
and 2005 Dietary Guidelines suggest a diet that is low in saturated fat, trans fat, and
cholesterol and provides 20 to 35 percent of the daily energy intake from fat. ◆ The
top end of this range is slightly higher than previous recommendations. This revi-
sion recognizes that diets with up to 35 percent of kcalories from fat can be compat-
ible with good health if energy intake is reasonable and saturated fat intake is low.
When total fat exceeds 35 percent, saturated fat increases to unhealthy levels.33 For
a 2000-kcalorie diet, 20 to 35 percent represents 400 to 700 kcalories from fat
(roughly 45 to 75 grams). Part of this fat allowance should provide for the essential
fatty acids—linoleic acid and linolenic acid. For this reason, an Adequate Intake (AI)
has been established for these two fatty acids. Recommendations suggest that
linoleic acid ◆ provide 5 to 10 percent of the daily energy intake and linolenic acid
◆ 0.6 to 1.2 percent.34
To help consumers meet the dietary fat goals, the Food and Drug Administration
(FDA) established Daily Values ◆ on food labels using 30 percent of energy intake
as the guideline for fat and 10 percent for saturated fat. The Daily Value for choles-
◆ DRI and 2005 Dietary Guidelines for fat:
• 20 to 35% of energy intake (from mostly
polyunsaturated and monounsaturated
fat sources such as fish, nuts, and veg-
etable oils)
◆ Linoleic acid (omega-6) AI:
Men:
• 19–50 yr: 17 g/day
• 51+ yr: 14 g/day
Women:
• 19–50 yr: 12 g/day
• 51+ yr: 11 g/day
◆ Linolenic acid (omega-3) AI:
• Men: 1.6 g/day
• Women: 1.1 g/day
◆ Daily Values:
• 65 g fat (based on 30% of 2000 kcal diet)
• 20 g saturated fat (based on 10% of 2000
kcal diet)
• 300 mg cholesterol

terol is 300 milligrams regardless of energy intake. There is no Daily Value for trans
fat, but consumers should try to keep intakes as low as possible and within the 10
percent allotted for saturated fat. According to surveys, adults in the United States
receive about 33 percent of their total energy from fat, with saturated fat contribut-
ing about 11 percent of the total. Cholesterol intakes in the United States average
190 milligrams a day for women and 290 for men. 35
Consume less than 10 percent of kcalories from saturated fatty acids and
less than 300 mg/day of cholesterol, and keep trans fatty acid consump-
tion as low as possible.
The fats of fish, nuts, and vegetable oils are not counted as discretionary kcalo-
ries because they provide valuable omega-3 fatty acids, essential fatty acids, and
vitamin E. In contrast, solid fats ◆ deliver an abundance of saturated fatty acids;
the USDA Food Guide counts them as discretionary kcalories. Discretionary kcalo-
ries may be used to add fats in cooking or at the table or to select higher fat items
from the food groups. ◆
Although it is very difficult to do, some people actually manage to eat too little
fat—to their detriment. Among them are people with eating disorders, described in
Highlight 8, and athletes. Athletes following a diet too low in fat (less than 20 per-
cent of total kcalories) fall short on energy, vitamins, minerals, and essential fatty
acids as well as on performance.36 As a practical guideline, it is wise to include the
equivalent of at least a teaspoon of fat in every meal—a little peanut butter on
toast or mayonnaise on tuna, for example. Dietary recommendations that limit fat
were developed for healthy people over age two; Chapter 15 discusses the fat needs
of infants and young children.
As the photos in Figure 5-23 show (p. 162), fat accounts for much of the energy
in foods, and removing the fat from foods cuts energy and saturated fat intakes
dramatically. To reduce dietary fat, eliminate fat as a seasoning and in cooking; re-
move the fat from high-fat foods; replace high-fat foods with low-fat alternatives;
and emphasize whole grains, fruits, and vegetables. The remainder of this chapter
identifies sources of fat in the diet, food group by food group.
Fats accompany protein in foods derived from animals, such as meat, fish, poultry,
and eggs, and fats accompany carbohydrate in foods derived from plants, such as av-
ocados and coconuts. Fats carry with them the four fat-soluble vitamins—A, D, E, and
K—together with many of the compounds that give foods their flavor, texture, and
palatability. Fat is responsible for the delicious aromas associated with sizzling bacon
and hamburgers on the grill, onions being sautéed, or vegetables in a stir-fry. Of
course, these wonderful characteristics lure people into eating too much from time to
time. With careful selections, a diet following the USDA Food Guide can support good
health and still meet fat recommendations (see the “How to” feature on p. 163).
Meats and Meat Alternates Many meats and meat alternates ◆ contain fat,
saturated fat, and cholesterol but also provide high-quality protein and valuable vi-
tamins and minerals. They can be included in a healthy diet if a person makes lean
choices and prepares them using the suggestions outlined in the box on p. 163. Se-
lecting “free-range” meats from grass-fed instead of grain-fed livestock offers the nu-
trient advantages of being lower in fat, and the fat has more polyunsaturated fatty
acids, including the omega-3 type. Another strategy to lower blood cholesterol is to
prepare meals using soy protein instead of animal protein.37
◆ Solid fats include meat and poultry fats (as
in poultry skin, luncheon meats, sausage);
milk fat (as in whole milk, cheese, butter);
shortening (as in fried foods and baked
goods); and hard margarines.
◆ The USDA Food Guide amounts of fats that
can be included as discretionary kcalories
when most food choices are nutrient dense
and fat 30% total kcal:
• 11 g for 1600 kcal diet
For perspective, 1 tsp oil = 5 g fat and pro-
vides about 45 kcal
◆ Very lean options:
• Chicken (white meat, no skin); cod,
flounder, trout; tuna (canned in water);
legumes
Lean options:
• Beef or pork “round” or “loin” cuts;
chicken (dark meat, no skin); herring or
salmon; tuna (canned in oil)
Medium-fat options:
• Ground beef, eggs, tofu
High-fat options:
• Sausage, bacon, luncheon meats, hot
dogs, peanut butter, nuts

162 • CHAPTER 5
Milks and Milk Products Like meats, milks and milk products ◆ should also be
selected with an awareness of their fat, saturated fat, and cholesterol contents. Fat-
free and low-fat milk products provide as much or more protein, calcium, and other
nutrients as their whole-milk versions—but with little or no saturated fat. Selecting
fermented milk products, such as yogurt, may also help to lower blood cholesterol.
These foods increase the population and activity of bacteria in the colon that fer-
ment fibers. As Chapter 4 explained, this action lowers blood cholesterol as fibers
bind with bile, thereby increasing excretion, and as bacteria produce short-chain
fatty acids that inhibit cholesterol synthesis in the liver.38
Vegetables, Fruits, and Grains Choosing vegetables, fruits, whole grains, and
legumes also helps lower the saturated fat, cholesterol, and total fat content of the
diet. Most vegetables and fruits naturally contain little or no fat. Although avocados
and olives are exceptions, most of their fat is unsaturated, which is not harmful to
heart health. Most grains contain only small amounts of fat. Consumers need to
read food labels, though, because some grain products such as fried taco shells, crois-
sants, and biscuits are high in saturated fat, and pastries, crackers, and cookies may
be high in trans fats. Similarly, many people add butter, margarine, or cheese sauce
Pork chop with fat (340 kcal, 19 g fat,
7 g saturated fat).
Potato with 1 tbs butter and 1 tbs sour
cream (350 kcal, 14 g fat, 10 g saturated
fat).
Whole milk, 1 c (150 kcal, 8 g fat, 5 g
saturated fat).
Pork chop with fat trimmed off (230 kcal,
9 g fat, 3 g saturated fat).
Plain potato (200 kcal, 1 g fat, 0 g
saturated fat).
Fat-free milk, 1 c (90 kcal, 1 g fat, 1 g
saturated fat).
FIGURE 5-23 Cutting Fat Cuts kCalories—and Saturated Fat
◆ Fat-free and low-fat options:
• Fat-free or 1% milk or yogurt (plain); fat-
free and low-fat cheeses
Reduced-fat options:
• 2% milk, low-fat yogurt (plain)
High-fat options:
• Whole milk, regular cheeses
©
Polara
Studios,
Inc.
(all)
When selecting and preparing meat, poultry, and milk or milk products,
make choices that are lean, low-fat, or fat-free.

to grains and vegetables, which raises their saturated and trans fat contents. Because
fruits are often eaten without added fat, a diet that includes several servings of fruit
daily can help a person meet the dietary recommendations for fat.
A diet rich in vegetables, fruits, whole grains, and legumes also offers abundant
vitamin C, folate, vitamin A, vitamin E, and dietary fiber—all important in sup-
porting health. Consequently, such a diet protects against disease by reducing sat-
urated fat, cholesterol, and total fat as well as by increasing nutrients. It also
provides valuable phytochemicals that help defend against heart disease.
Invisible Fat Visible fat, such as butter and the fat trimmed from meat, is easy to
see. Invisible fat is less apparent and can be present in foods in surprising amounts.
Invisible fat “marbles” a steak or is hidden in foods like cheese. Any fried food con-
tains abundant fat—potato chips, French fries, fried wontons, and fried fish. Many
baked goods, too, are high in fat—pie crusts, pastries, crackers, biscuits, cornbread,
doughnuts, sweet rolls, cookies, and cakes. Most chocolate bars deliver more kcalo-
ries from fat than from sugar. Even cream-of-mushroom soup prepared with water
derives 66 percent of its energy from fat. Keep invisible fats in mind when making
food selections.
Breads and Cereals
• Select breads, cereals, and crackers that are
low in saturated and trans fat (for example,
bagels instead of croissants).
• Prepare pasta with a tomato sauce instead
of a cheese or cream sauce.
Vegetables and Fruits
• Enjoy the natural flavor of steamed vegeta-
bles (without butter) for dinner and fruits
for dessert.
• Eat at least two vegetables (in addition to a
salad) with dinner.
• Snack on raw vegetables or fruits instead of
high-fat items like potato chips.
• Buy frozen vegetables without sauce.
Milk and Milk Products
• Switch from whole milk to reduced-fat,
from reduced-fat to low-fat, and from low-
fat to fat-free (nonfat).
• Use fat-free and low-fat cheeses (such as
part-skim ricotta and low-fat mozzarella)
instead of regular cheeses.
• Use fat-free or low-fat yogurt or sour cream
instead of regular sour cream.
• Use evaporated fat-free milk instead of
cream.
• Enjoy fat-free frozen yogurt, sherbet, or ice
milk instead of ice cream.
Meat and Legumes
• Fat adds up quickly, even with lean meat;
limit intake to about 6 ounces (cooked
weight) daily.
• Eat at least two servings of fish per week
(particularly fish such as mackerel, lake
trout, herring, sardines, and salmon).
• Choose fish, poultry, or lean cuts of pork or
beef; look for unmarbled cuts named round
or loin (eye of round, top round, bottom
round, round tip, tenderloin, sirloin, center
loin, and top loin).
• Choose processed meats such as lunch
meats and hot dogs that are low in satu-
rated fat and cholesterol.
• Trim the fat from pork and beef; remove
the skin from poultry.
• Grill, roast, broil, bake, stir-fry, stew, or
braise meats; don’t fry. When possible,
place food on a rack so that fat can drain.
• Use lean ground turkey or lean ground
beef in recipes; brown ground meats
without added fat, then drain off fat.
• Select tuna, sardines, and other canned
meats packed in water; rinse oil-packed
items with hot water to remove much of
the fat.
• Fill kabob skewers with lots of vegetables
and slivers of meat; create main dishes and
casseroles by combining a little meat, fish, or
poultry with a lot of pasta, rice, or vegetables.
• Use legumes often.
• Eat a meatless meal or two daily.
• Use egg substitutes in recipes instead of
whole eggs or use two egg whites in place
of each whole egg.
Fats and Oils
• Use butter or stick margarine sparingly;
select soft margarines instead of hard
margarines.
• Use fruit butters, reduced-kcalorie mar-
garines, or butter replacers instead of
butter.
• Use low-fat or fat-free mayonnaise and
salad dressing instead of regular.
• Limit use of lard and meat fat.
• Limit use of products made with coconut
oil, palm kernel oil, and palm oil (read
labels on bakery goods, processed foods,
popcorn oils, and nondairy creamers).
• Reduce use of hydrogenated shortenings
and stick margarines and products that
contain them (read labels on crackers,
cookies, and other commercially prepared
baked goods); use vegetable oils instead.
Miscellaneous
• Use a nonstick pan or coat the pan lightly
with vegetable oil.
• Refrigerate soups and stews; when the fat
solidifies, remove it.
• Use wine; lemon, orange, or tomato juice;
herbs; spices; fruits; or broth instead of
butter or margarine when cooking.
• Stir-fry in a small amount of oil; add mois-
ture and flavor with broth, tomato juice,
or wine.
• Use variety to enhance enjoyment of the
meal: vary colors, textures, and tempera-
tures—hot cooked versus cool raw foods—
and use garnishes to complement food.
• Omit high-fat meat gravies and cheese
sauces.
SOURCE: Adapted from Third Report of the National Cholesterol
Education Program (NCEP) Expert Panel on Detection, Evaluation,
and Treatment of High Blood Cholesterol in Adults (Adult
Treatment Panel III), NIH publication no. 02-5215 (Bethesda,
Md.: National Heart, Lung, and Blood Institute, 2002),
pp. V-25–V-27.
HOW TO Make Heart-Healthy Choices—by Food Group

164 • CHAPTER 5
Choose Wisely Consumers can find an abundant array of foods that are low in
saturated fat, trans fat, cholesterol, and total fat. In many cases, they are familiar
foods that are simply prepared with less fat. For example, fat can be removed by
skimming milk or trimming meats. Manufacturers can dilute fat by adding water or
whipping in air. They can use fat-free milk in creamy desserts and lean meats in
frozen entrées. Sometimes manufacturers simply prepare the products differently.
For example, fat-free potato chips may be baked instead of fried. Beyond lowering
the fat content, manufacturers have developed margarines fortified with plant
sterols that lower blood cholesterol.*39 (Highlight 13 explores these and other func-
tional foods designed to support health.) Such choices make heart-healthy eating
easy.
Limit intakes of fats and oils high in saturated and/or trans fatty acids, and
choose products low in such fats and oils.
To replace saturated fats with unsaturated fats, sauté foods in olive oil instead of
butter, garnish salads with sunflower seeds instead of bacon, snack on mixed nuts
instead of potato chips, use avocado instead of cheese on a sandwich, and eat
salmon instead of steak. Table 5-3 shows how these simple substitutions can lower
the saturated fat and raise the unsaturated fat in a meal. Highlight 5 provides more
details about the benefits of healthy fats in the diet.
Fat Replacers Some foods are made with fat replacers—ingredients derived from
carbohydrate, protein, or fat that can be used to replace some or all of the fat in foods.
The body may digest and absorb some of these substances, so they may contribute
some energy, although significantly less energy than fat’s 9 kcalories per gram.
Fat replacers offering the sensory and cooking qualities of fats but none of the
kcalories are called artificial fats. A familiar example of an artificial fat that has
been approved for use in snack foods such as potato chips, crackers, and tortilla
chips is olestra. Olestra’s chemical structure is similar to that of a regular fat (a
triglyceride) but with important differences. A triglyceride is composed of a glycerol
molecule with three fatty acids attached, whereas olestra is made of a sucrose mol-
TABLE 5-3 Choosing Unsaturated Fat instead of Saturated Fat
Portion sizes have been adjusted so that each of these foods provides approximately 100 kcalories.
Notice that for a similar number of kcalories and grams of fat, the first choices offer less saturated
fat and more unsaturated fat.
Saturated Unsaturated Total
Foods (100 kcal portions) Fat (g) Fat (g) Fat (g)
Olive oil (1tbs) vs. butter (1tbs) 2 vs. 7 9 vs. 4 11 vs. 11
Sunflower seeds (2 tbs) vs. bacon (2 slices) 1 vs. 3 7 vs. 6 8 vs. 9
Mixed nuts (2 tbs) vs. potato chips (10 chips) 1 vs. 2 8 vs. 5 9 vs. 7
Avocado (6 slices) vs. cheese (1 slice) 2 vs. 4 8 vs. 4 10 vs. 8
Salmon (2 oz) vs. steak (11/2 oz) 1 vs. 2 3 vs. 3 4 vs. 5
Totals 7 vs. 18 35 vs. 22 42 vs. 40
* Margarines that lower blood cholesterol contain plant sterols and are marketed under the brand
names Benecol and Take Control.
fat replacers: ingredients that replace some
or all of the functions of fat and may or may
not provide energy.
artificial fats: zero-energy fat replacers that
are chemically synthesized to mimic the
sensory and cooking qualities of naturally
occurring fats but are totally or partially
resistant to digestion.
olestra: a synthetic fat made from sucrose
and fatty acids that provides 0 kcalories per
gram; also known as sucrose polyester.
Well-balanced, healthy meals provide some fat
with an emphasis on monounsaturated and
polyunsaturated fats.
©
Polara
Studios
Inc.

ecule with six to eight fatty acids attached. Enzymes in the digestive tract cannot
break the bonds of olestra, so unlike sucrose or fatty acids, olestra passes through
the system unabsorbed.
The FDA’s evaluation of olestra’s safety addressed two questions. First, is
olestra toxic? Research on both animals and human beings supports the
safety of olestra as a partial replacement for dietary fats and oils, with no re-
ports of cancer or birth defects. Second, does olestra affect either nutrient ab-
sorption or the health of the digestive tract? When olestra passes through the
digestive tract unabsorbed, it binds with some of the fat-soluble vitamins A, D,
E, and K and carries them out of the body, robbing the person of these valu-
able nutrients. To compensate for these losses, the FDA requires the manufac-
turer to fortify olestra with vitamins A, D, E, and K. Saturating olestra with
these vitamins does not make the product a good source of vitamins, but it
does block olestra’s ability to bind with the vitamins from other foods. An as-
terisk in the ingredients list informs consumers that these added vitamins are
“dietarily insignificant.”
Some consumers experience digestive distress with olestra consumption, such
as cramps, gas, bloating, and diarrhea. The FDA initially required a label warn-
ing stating that “olestra may cause abdominal cramping and loose stools” and
that it “inhibits the absorption of some vitamins and other nutrients” but has
since concluded that such a statement is no longer warranted.
Consumers need to keep in mind that low-fat and fat-free foods still deliver
kcalories. Alternatives to fat can help to lower energy intake and support weight
loss only when they actually replace fat and energy in the diet.40
Read Food Labels Labels list total fat, saturated fat, trans fat, and cholesterol
contents of foods in addition to fat kcalories per serving (see Figure 5-24, p. 166). Be-
cause each package provides information for a single serving and because serving
sizes are standardized, consumers can easily compare similar products.
Total fat, saturated fat, and cholesterol are also expressed as “% Daily Values”
for a person consuming 2000 kcalories. People who consume more or less than
2000 kcalories daily can calculate their personal Daily Value for fat as described in
the “How to” below. Trans fats do not have a Daily Value.
Beware of fast-food meals delivering too much
fat, especially saturated fat. This double bacon
cheeseburger, fries, and milkshake provide
more than 1600 kcalories, with almost 90
grams of fat and over 30 grams of saturated
fat—far exceeding dietary fat guidelines for the
entire day.
HOW TO Calculate a Personal Daily Value for Fat
The % Daily Value for fat on food labels is
based on 65 grams. To know how your intake
compares with this recommendation, you
can either count grams until you reach 65, or
add the “% Daily Values” until you reach 100
percent—if your energy intake is 2000 kcalo-
ries a day. If your energy intake is more or
less, you can calculate your personal daily fat
allowance in grams. Suppose your energy
intake is 1800 kcalories per day and your goal
is 30 percent kcalories from fat. Multiply your
total energy intake by 30 percent, then divide
by 9:
1800 total kcal 0.30 from fat 540 fat kcal
540 fat kcal 9 kcal/g 60 g fat
(In familiar measures, 60 grams of fat is about
the same as 2
/3 stick of butter or
1
/4cup of oil.)
The accompanying table shows the numbers of
grams of fat allowed per day for various energy
intakes. With one of these numbers in mind,
you can quickly evaluate the number of fat
grams in foods you are considering eating.
Energy 20% kCalories 35% kCalories Fat
(kcal/day) from Fat from Fat (g/day)
1200 240 420 27–47
1400 280 490 31–54
1600 320 560 36–62
1800 360 630 40–70
2000 400 700 44–78
2200 440 770 49–86
2400 480 840 53–93
2600 520 910 58–101
2800 560 980 62–109
3000 600 1050 67–117
To practice calculating a personal daily value for fat,
log on to academic.cengage.com/login, go to
Matthew
Farruggio

166 • CHAPTER 5
Be aware that the “% Daily Value” for fat is not the same as “% kcalories from
fat.” This important distinction is explained in the “How to” feature on p. 167. Be-
cause recommendations apply to average daily intakes rather than individual food
items, food labels do not provide “% kcalories from fat.” Still, you can get an idea
of whether a particular food is high or low in fat.
INGREDIENTS: Cream, salt.
Total Fat 11g 17%
37%
*Percent Daily Values are based on a
2,000 calorie diet.
Serving Size 1 Tbsp (14g)
Servings per container about 32
Calories 100 Calories from Fat 100
Amount per serving
%Daily Value*
Sodium 95mg
Cholesterol 30mg
4%
0%
10%
Protein 0g
Not a significant source of dietary fiber,
sugars, vitamin C, calcium, and iron.
Saturated Fat 7g
Trans Fat 0g
Vitamin A 8%
Nutrition Facts
INGREDIENTS: Liquid
soybean oil, partially
hydrogenated soybean oil,
water, buttermilk, salt, soy
lecithin, sodium benzoate (as a
preservative), vegetable mono
and diglycerides, artificial
flavor, vitamin A palmitate,
colored with beta carotene
(provitamin A).
Total Fat 11g 17%
11%
2,000 calorie diet.
Serving Size 1 Tbsp (14g)
Amount per serving
%Daily Value*
Sodium 105mg
Cholesterol 0mg
4%
0%
0%
Protein 0g
Saturated Fat 2g
Trans Fat 2.5g
Polyunsaturated Fat 3.5g
Monounsaturated Fat 2.5g
Vitamin A 10%
Nutrition Facts
INGREDIENTS: Liquid
soybean oil, partially
hydrogenated soybean oil,
buttermilk, water, butter (cream,
salt), salt, soy lecithin,
vegetable mono and
diglycerides, sodium benzoate
added as a preservative,
artificial flavor, vitamin A
palmitate, colored with beta
carotene.
Total Fat 11g 17%
13%
2,000 calorie diet.
Serving size 1 Tbsp (14g)
Amount per serving
%Daily Value*
Sodium 80mg
Cholesterol 0mg
3%
0%
0%
Protein 0g
Saturated Fat 2.5g
Trans Fat 2g
Polyunsaturated Fat 4g
Monounsaturated Fat 2.5g
Vitamin A 10%
Nutrition Facts
INGREDIENTS: Liquid
soybean oil, water, salt,
hydrogenated cottonseed oil,
vegetable monoglycerides and
soy lecithin (emulsifiers),
potassium sorbate and sodium
benzoate (to preserve
freshness), artificial flavor,
phosphoric acid (acidulant),
colored with beta carotene
(source of vitamin A), vitamin A
palmitate.
Total Fat 8g 13%
7%
2,000 calorie diet.
Serving size 1 Tbsp (14g)
Amount per serving
%Daily Value*
Sodium 110mg
Cholesterol 0mg
8%
0%
0%
Protein 0g
Saturated Fat 1.5g
Polyunsaturated Fat 4.5g
Monounsaturated Fat 2g
Vitamin A 10%
Nutrition Facts
Trans Fat 0g
Butter Margarine (stick) Margarine (liquid)
Margarine (tub)
FIGURE 5-24 Butter and Margarine Labels Compared
Food labels list the kcalories from fat; the quantities and Daily Values for fat, saturated fat, and cholesterol; and the quantities
for trans fat. Information on polyunsaturated and monounsaturated fats is optional. In this example, stick margarine has 2.5 g
trans fat and tub margarine has 2 g trans fat. Products that contain 0.5 g or less of trans fat and 0.5 g or less of saturated fat may
claim “no trans fat.” Similarly, products that contain 2 mg or less of cholesterol and 2 g or less of saturated fat may claim to be
“cholesterol-free.”
If the list of ingredients includes hydrogenated oils, you know the food contains trans fat. Chapter 2 explained that foods list
their ingredients in descending order of predominance by weight. As you can see from this example, the closer “partially hydro-
genated oils” is to the beginning of the ingredients list, the more trans fats the product contains. Notice that most of the fat in
butter is saturated, whereas most of the fat in margarine is unsaturated; partially hydrogenated margarines tend to have more
trans fat than hydrogenated liquid margarines.

If people were to make only one change in their diets, they would be wise to limit
their intakes of saturated fat. Sometimes these choices can be difficult, though, be-
cause fats make foods taste delicious. To maintain good health, must a person give
up all high-fat foods forever—never again to eat marbled steak, hollandaise sauce,
or gooey chocolate cake? Not at all. These foods bring pleasure to a meal and can be
enjoyed as part of a healthy diet when eaten occasionally in small quantities; but
they should not be everyday foods. The key word for fat is moderation, not depriva-
tion. Appreciate the energy and enjoyment that fat provides, but take care not to ex-
ceed your needs.
The “% Daily Value” that is used on food
labels to describe the amount of fat in a
food is not the same as the “% kcalories
from fat” that is used in dietary recommen-
dations to describe the amount of fat in the
diet. They may appear similar, but their
difference is worth understanding. Consider,
for example, a piece of lemon meringue pie
that provides 140 kcalories and 12 grams of
fat. Because the Daily Value for fat is 65
grams for a 2000-kcalorie intake, 12 grams
represent about 18 percent:
12 g 65 g 0.18
0.18 100 18%
The pie’s “% Daily Value” is 18 percent, or
almost one-fifth, of the day’s fat allowance.
Uninformed consumers may mistakenly
believe that this food meets recommenda-
tions to limit fat to “20 to 35 percent kcalo-
ries,”but it doesn’t—for two reasons. First,
the pie’s 12 grams of fat contribute 108 of
the 140 kcalories, for a total of 77 percent
kcalories from fat:
12 g fat 9 kcal/g 108 kcal
108 kcal 140 kcal 77%
Second, the “percent kcalories from fat”
guideline applies to a day’s total intake, not
to an individual food. Of course, if every
selection throughout the day exceeds 35
percent kcalories from fat, you can be cer-
tain that the day’s total intake will, too.
HOW TO Understand “% Daily Value” and “% kCalories from Fat” To practice calculating % Daily Value and % kcalories
from fat, log on to academic.cengage.com/
login, go to Chapter 5, then go to How To.
In foods, triglycerides:
• Deliver fat-soluble vitamins, energy, and essential fatty acids
• Contribute to the sensory appeal of foods and stimulate appetite
Although some fat in the diet is necessary, health authorities recommend a
diet moderate in total fat and low in saturated fat, trans fat, and cholesterol.
They also recommend replacing saturated fats with monounsaturated and
polyunsaturated fats, particularly omega-3 fatty acids from foods such as fish,
not from supplements. Many selection and preparation strategies can help
bring these goals within reach, and food labels help to identify foods consis-
tent with these guidelines.
IN SUMMARY
Whether a person’s energy and fat
allowance can afford a piece of lemon
meringue pie depends on the other food
and activity choices made that day.
©
PhotoDisc/Getty
Images

168 • CHAPTER 5
To maintain good health, eat enough, but not too much, fat and select the right
kinds.
■ List the types and amounts of fats and oils you eat daily, making note of which
ones are saturated, monounsaturated, or polyunsaturated and how your choices
could include fewer saturated options.
■ List the types and amounts of milk products, meats, fish, and poultry you eat
daily, noting how your choices could include more low-fat options.
■ Describe choices you can make in selecting and preparing foods to lower your
intake of solid fats.
Nutrition Portfolio
• Search for “cholesterol” and “dietary fat” at the U.S. Gov-
ernment health information site: www.healthfinder.gov
• Search for “fat” at the International Food Information
Council site: www.ific.org
• Find dietary strategies to prevent heart disease at the
American Heart Association or National Heart, Lung, and
Blood Institute: www.americanheart.org or nhlbi.nih.gov
nutrition-related calculations (see p. 171 for answers). Show
your calculations for each problem.
1. Be aware of the fats in milks. Following are four
categories of milk.
Wt (g) Fat (g) Prot (g) Carb (g)
Milk A (1 c) 244 8 8 12
Milk B (1 c) 244 5 8 12
Milk C (1 c) 244 3 8 12
Milk D (1 c) 244 0 8 12
a. Based on weight, what percentage of each milk is fat
(round off to a whole number)?
b. How much energy from fat will a person receive from
drinking 1 cup of each milk?
c. How much total energy will the person receive from 1
cup of each milk?
d. What percentage of the energy in each milk comes
from fat?
e. In the grocery store, how is each milk labeled?
2. Judge foods’ fat contents by their labels.
a. A food label says that one serving of the food contains
6.5 grams fat. What would the % Daily Value for fat be?
What does the Daily Value you just calculated mean?
b. How many kcalories from fat does a serving contain?
(Round off to the nearest whole number.)
c. If a serving of the food contains 200 kcalories, what
percentage of the energy is from fat?
This example should show you how easy it is to evaluate
foods’ fat contents by reading labels and to see the difference
between the % Daily Value and the percentage of kcalories
from fat.
3. Now consider a piece of carrot cake. Remember that the
Daily Value suggests 65 grams of fat as acceptable within
a 2000-kcalorie diet. A serving of carrot cake provides 30
grams of fat. What percentage of the Daily Value is that?
What does this mean?

1. Name three classes of lipids found in the body and in
foods. What are some of their functions in the body?
What features do fats bring to foods? (pp. 139, 145, 147,
153–155, 161)
2. What features distinguish fatty acids from each other?
(pp. 139–142)
3. What does the term omega mean with respect to fatty
acids? Describe the roles of the omega fatty acids in dis-
ease prevention. (pp. 141–142, 158–159)
4. What are the differences between saturated, unsaturated,
monounsaturated, and polyunsaturated fatty acids?
Describe the structure of a triglyceride. (pp. 140–143)
5. What does hydrogenation do to fats? What are trans-
fatty acids, and how do they influence heart disease?
(pp. 143–144, 157)
6. How do phospholipids differ from triglycerides in struc-
ture? How does cholesterol differ? How do these differ-
ences in structure affect function? (pp. 145–147)
7. What roles do phospholipids perform in the body? What
roles does cholesterol play in the body? (pp. 145–147)
8. Trace the steps in fat digestion, absorption, and trans-
port. Describe the routes cholesterol takes in the body.
(pp. 147–153)
9. What do lipoproteins do? What are the differences among
the chylomicrons, VLDL, LDL, and HDL? (pp. 150–153)
10. Which of the fatty acids are essential? Name their chief
dietary sources. (pp. 154–155)
11. How does excessive fat intake influence health? What
factors influence LDL, HDL, and total blood cholesterol?
(pp. 156–160)
12. What are the dietary recommendations regarding fat
and cholesterol intake? List ways to reduce intake.
(pp. 160–165)
13. What is the Daily Value for fat (for a 2000-kcalorie diet)?
What does this number represent? (pp. 165–167)
1. Saturated fatty acids:
a. are always 18 carbons long.
b. have at least one double bond.
c. are fully loaded with hydrogens.
d. are always liquid at room temperature.
2. A triglyceride consists of:
a. three glycerols attached to a lipid.
b. three fatty acids attached to a glucose.
c. three fatty acids attached to a glycerol.
d. three phospholipids attached to a cholesterol.
3. The difference between cis- and trans-fatty acids is:
a. the number of double bonds.
b. the length of their carbon chains.
c. the location of the first double bond.
d. the configuration around the double bond.
4. Which of the following is not true? Lecithin is:
a. an emulsifier.
b. a phospholipid.
c. an essential nutrient.
d. a constituent of cell membranes.
5. Chylomicrons are produced in the:
a. liver.
b. pancreas.
c. gallbladder.
d. small intestine.
6. Transport vehicles for lipids are called:
a. micelles.
b. lipoproteins.
c. blood vessels.
d. monoglycerides.
7. The lipoprotein most associated with a high risk of heart
disease is:
a. CHD.
b. HDL.
c. LDL.
d. LPL.
8. Which of the following is not true? Fats:
a. contain glucose.
b. provide energy.
c. protect against organ shock.
d. carry vitamins A, D, E, and K.
9. The essential fatty acids include:
a. stearic acid and oleic acid.
b. oleic acid and linoleic acid.
c. palmitic acid and linolenic acid.
d. linoleic acid and linolenic acid.
10. A person consuming 2200 kcalories a day who wants to
meet health recommendations should limit daily fat
intake to:
a. 20 to 35 grams.
b. 50 to 85 grams.
c. 75 to 100 grams.
d. 90 to 130 grams.
STUDY QUESTIONS

170 • CHAPTER 5
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9. P. J. Nestel and coauthors, Relation of diet
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11. J. Dyerberg and coauthors, Effects of trans-
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12. D. Mozaffarian and coauthors, Trans fatty
acids and systemic inflammation in heart
failure, American Journal of Clinical Nutrition
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thors, Dietary fatty acids affect plasma
markers of inflammation in healthy men
fed controlled diets: A randomized crossover
study, American Journal of Clinical Nutrition
79 (2004): 969–973; D. Mozaffarian and
coauthors, Dietary intake of trans fatty acids
and systemic inflammation in women,
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13. Federal Register 68, July 11, 2003, p. 41444.
14. Expert Panel on Detection, Evaluation, and
Treatment of High Blood Cholesterol in
Adults (Adult Treatment Panel III), Third
Report of the National Cholesterol Education
Program (NCEP), NIH publication no. 02-
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and Blood Institute, 2002), p. V-10.
15. A. H. Stark and Z. Madar, Olive oil as a
functional food: Epidemiology and nutri-
tional approaches, Nutrition Reviews 60
(2002): 170–176.
16. P. M. Kris-Etherton, K. D. Hecker, and A. E.
Binkoski, Polyunsaturated fatty acids and
cardiovascular health, Nutrition Reviews 62
(2004): 414–426.
17. J. L. Breslow, n-3 Fatty acids and cardiovas-
cular disease, American Journal of Clinical
Nutrition 83 (2006): 1477S–1482S; F. B. Hu
and coauthors, Fish and omega-3 fatty acid
intake and risk of coronary heart disease in
women, Journal of the American Medical
Association 287 (2002): 1815–1821; C. M.
Albert and coauthors, Blood levels of long-
chain n-3 fatty acids and the risk of sudden
death, New England Journal of Medicine 346
(2002): 1113–1118.
18. Breslow, 2006; P. J. H. Jones and V. W. Y.
Lau, Effect of n-3 polyunsaturated fatty
acids on risk reduction of sudden death,
Nutrition Reviews 60 (2002): 407–413.
19. M. C. Nesheim and A. L. Yaktine, eds.,
Seafood, Seafood Choices: Balancing Benefits
and Risks (Washington, D. C.: National
Academies Press, 2007), p. 12; C. W. Leven-
son and D. M. Axelrad, Too much of a good
thing? Update on fish consumption and
murcury exposure, Nutrition Reviews 64
(2006): 139–145; E. Guallar and coauthors,
Mercury, fish oils, and the risk of myocar-
dial infarction, New England Journal of Medi-
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20. V. Wijendran and K. C. Hayes, Dietary n-6
and n-3 fatty acid balance and cardiovascu-
lar health, Annual Review of Nutrition 24
(2004): 597–615.
21. AHA Scientific statement: Diet and lifestyle
recommendations revision 2006, Circulation
114 (2006): 82–96
22. K. He and coauthors, Fish consumption and
risk of stroke in men, Journal of the American
23. L. Cordain and coauthors, Fatty acid analy-
sis of wild ruminant tissues: Evolutionary
implications for reducing diet-related
chronic disease, European Journal of Clinical
Nutrition 56 (2002): 181–191.
24. S. Bechoua and coauthors, Influence of very
low dietary intake of marine oil on some
functional aspects of immune cells in
healthy elderly people, British Journal of
Nutrition 89 (2003): 523–532.
25. M. H. Raitt and coauthors, Fish oil supple-
mentation and risk of ventricular tachycar-
dia and ventricular fibrillation in patients
with implantable defibrillators: A random-
ized control study, Journal of the American
Medical Association 293 (2005): 2884–2891;
P. M. Kris-Etherton and coauthors, AHA
Scientific Statement: Fish consumption, fish
oil, omega-3 fatty acids, and cardiovascular
disease, Circulation 106 (2002): 2747–2757.
26. C. B. Stephensen, Fish oil and inflammatory
disease: Is asthma the next target for n-3
fatty acid supplements? Nutrition Reviews 62
(2004): 486–489.
27. G. L. Khor, Dietary fat quality: A nutritional
epidemiologist’s view, Asia Pacific Journal of
Clinical Nutrition 13 (2004): S22; R. Stoeckli
and U. Keller, Nutritional fats and the risk of
type 2 diabetes and cancer, Physiology and
Behavior 83 (2004): 611–615.
28. M. D. Holmes and W. C. Willett, Does diet
affect breast cancer risk? Breast Cancer Re-
search 6 (2004): 170–178.
29. L. K. Dennis and coauthors, Problems with
the assessment of dietary fat in prostate
cancer studies, American Journal of Epidemiol-
ogy 160 (2004): 436–444.
30. P. W. Parodi, Dairy product consumption
and the risk of breast cancer, Journal of the
American College of Nutrition 24 (2005):
556S–568S; J. Zhang and H. Kesteloot, Milk
consumption in relation to incidence of
prostate, breast, colon, and rectal cancers: Is
there an independent effect? Nutrition and
Cancer 53 (2005): 65–72.
31. C. H. MacLean and coauthors, Effects of
omega-3 fatty acids on cancer risk-A system-
atic review, Journal of the American Medical
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man, (n-3) Fatty acids and cancer therapy,
Journal of Nutrition 134 (2004): 3427S–3430S;
M. F. Leitzmann and coauthors, Dietary
intake of n-3 and n-6 fatty acids and the risk
of prostate cancer, American Journal of Clinical
Nutrition 80 (2004): 204–216; S. C. Larsson
and coauthors, Dietary long-chain n-3 fatty
acids for the prevention of cancer: A review
of potential mechanisms, American Journal of
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National Academies Press, 2002/2005).
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Clinical Nutrition 76 (2002): 351–358; D. J. A.
Jenkins and coauthors, Soluble fiber intake
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of Clinical Nutrition 75 (2002): 834–839.
39. C. S. Patch, L. C. Tapsell, and P. G. Williams,
Plant sterol/stanol prescription is an effec-
tive treatment strategy for managing hyper-
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practice, Journal of the American Dietetic
Association 105 (2005): 46–52.
tion: Fat replacers, Journal of the American
1. a. Milk A: 8 g fat 244 g total 0.03; 0.03 100 = 3%
Milk B: 5 g fat 244 g total 0.02; 0.02 100 = 2%
Milk C: 3 g fat 244 g total 0.01; 0.01 100 = 1%
Milk D: 0 g fat 244 g total 0.00; 0.00 100 = 0%
b. Milk A: 8 g fat 9 kcal/g 72 kcal from fat
Milk B: 5 g fat 9 kcal/g 45 kcal from fat
Milk C: 3 g fat 9 kcal/g 27 kcal from fat
Milk D: 0 g fat 9 kcal/g 0 kcal from fat
c. Milk A: (8 g fat 9 kcal/g) (8 g prot 4 kcal/g)
(12 g carb 4 kcal/g) 152 kcal
Milk B: (5 g fat 9 kcal/g) (8 g prot 4 kcal/g)
Milk C: (3 g fat 9 kcal/g) (8 g prot 4 kcal/g)
Milk D: (0 g fat 9 kcal/g) (8 g prot 4 kcal/g)
d. Milk A: 72 kcal from fat 152 total kcal 0.47;
0.47 100 47%
Milk B: 45 kcal from fat 125 total kcal 0.36;
0.36 100 36%
Milk C: 27 kcal from fat 107 total kcal 0.25;
0.25 100 25%
Milk D: 0 kcal from fat 80 total kcal 0.00;
0.00 100 0%
e. Milk A: whole
Milk B: reduced-fat, 2%, or less-fat
Milk C: low-fat or 1%
Milk D: fat-free, nonfat, skim, zero-fat, or no-fat
2. a. 6.5 g 65 g 0.1; 0.1 100 10%; a Daily Value of
10% means that one serving of this food contributes about
1
⁄10 of the day’s fat allotment
b. 6.5 g 9 kcal/g 58.5, rounded to 59 kcal from fat
c. (59 kcal from fat 200 kcal) 100 30% kcalories from
fat
3. (30 g fat 65 g fat) 100 46% of the Daily Value for fat;
this means that almost half of the day’s fat allotment would be
used in this one dessert
1. c 2. c 3. d 4. c 5. d 6. b 7. c 8. a
9. d 10. b
ANSWERS

HIGHLIGHT 5
High-Fat Foods—Friend or Foe?
172
Eat less fat. Eat more fatty fish. Give up butter.
Use margarine. Give up margarine. Use olive
oil. Steer clear of saturated. Seek out omega-
3. Stay away from trans. Stick with mono-
and polyunsaturated. Keep fat intake moder-
ate. Today’s fat messages seem to be forever
multiplying and changing. No wonder peo-
ple feel confused about dietary fat. The con-
fusion stems in part from the complexities of fat and in part from
the nature of recommendations. As Chapter 5 explained, “dietary
fat” refers to several kinds of fats. Some fats support health
whereas others damage it, and foods typically provide a mixture
of fats in varying proportions. Researchers have spent decades
sorting through the relationships among the various kinds of fat
and their roles in supporting or harming health. Translating these
research findings into dietary recommendations is challenging.
Too little information can mislead consumers, but too much de-
tail can overwhelm them. As research findings accumulate, rec-
ommendations slowly evolve and become more refined.
Fortunately, that’s where we are with fat recommendations to-
day—refining them from the general to the specific. Though they
may seem to be “forever multiplying and changing,” in fact, they
are becoming more meaningful.
This highlight begins with a look at the dietary guidelines for
fat intake. It continues by identifying which foods provide which
fats and presenting the Mediterranean diet, an example of a food
plan that embraces the heart-healthy fats. It closes with strategies
to help consumers choose the right amounts of the right kinds of
fats for a healthy diet.
Guidelines for Fat Intake
Dietary recommendations for fat have changed in recent years,
shifting the emphasis from lowering total fat, in general, to limit-
ing saturated and trans fat, specifically. For decades, health ex-
perts advised limiting intakes of total fat to 30 percent or less of
energy intake. They recognized that saturated fats and trans fats
are the fats that raise blood cholesterol but reasoned that by lim-
iting total fat intake, saturated and trans fat intake would decline
as well. People were simply advised to cut back on all fat and
thereby they would cut back on saturated and trans fat. Such ad-
vice may have oversimplified the message and unnecessarily re-
stricted total fat.
Low-fat diets have a place in treatment plans for people with
elevated blood lipids or heart disease, but some researchers ques-
tion the wisdom of such diets for healthy people as a means of
controlling weight and preventing diseases. Several problems ac-
company low-fat diets. For one, many people
find low-fat diets difficult to maintain over
time. For another, low-fat diets are not neces-
sarily low-kcalorie diets. If energy intake ex-
ceeds energy needs, weight gain follows, and
obesity brings a host of health problems, in-
cluding heart disease. For still another, diets
extremely low in fat may exclude fatty fish,
nuts, seeds, and vegetable oils—all valuable sources of many es-
sential fatty acids, phytochemicals, vitamins, and minerals. Im-
portantly, the fats from these sources protect against heart
disease, as later sections of this highlight explain.
Instead of urging people to cut back on all fats, current recom-
mendations suggest carefully replacing the “bad” saturated fats
with the “good” unsaturated fats and enjoying them in modera-
tion.1 The goal is to create a diet moderate in kcalories that pro-
vides enough of the fats that support good health, but not too
much of those that harm health. (Turn to pp. 156–160 for a re-
view of the health consequences of each type of fat.)
With these findings and goals in mind, the DRI committee sug-
gests a healthy range of 20 to 35 percent of energy intake from
fat. This range appears to be compatible with low rates of heart
disease, diabetes, obesity, and cancer.2 Heart-healthy recommen-
dations suggest that within this range, consumers should try to
minimize their intakes of saturated fat, trans fat, and cholesterol
and use monounsaturated and polyunsaturated fats instead.3
Asking consumers to limit their total fat intake was less than
perfect advice, but it was straightforward—find the fat and cut
back. Asking consumers to keep their intakes of saturated fats,
trans fats, and cholesterol low and to use monounsaturated and
polyunsaturated fats instead may be more on target with heart
health, but it also makes diet planning more complicated. To
make appropriate selections, consumers must first learn which
foods contain which fats.
High-Fat Foods and Heart
Health
Avocados, bacon, walnuts, potato chips, and mackerel are all
high-fat foods, yet some of these foods have detrimental effects
on heart health when consumed in excess, whereas others seem
neutral or even beneficial. This section presents some of the accu-
mulating evidence that helped to distinguish which high-fat
foods belong in a healthy diet and which ones need to be kept to
a minimum. As you will see, a little more fat in the diet may be
©
Philip
Salverry/FoodPix/Jupiter
Images

compatible with heart health, but only if the great majority of it is
the unsaturated kind.
Cook with Olive Oil
As it turns out, the traditional diets of Greece and other countries
in the Mediterranean region offer an excellent example of eating
patterns that use “good” fats liberally. Often, these diets are rich
in olives and their oil. A classic study of the world’s people, the
Seven Countries Study, found that death rates from heart disease
were strongly associated with diets high in saturated fats but only
weakly linked with total fat.4 In fact, the two countries with the
highest fat intakes, Finland and the Greek island of Crete, had the
highest (Finland) and lowest (Crete) rates of heart disease deaths.
In both countries, the people consumed 40 percent or more of
their kcalories from fat. Clearly, a high-fat diet was not the pri-
mary problem, so researchers refocused their attention on the
type of fat. They began to notice the benefits of olive oil.
A diet that uses olive oil instead of other cooking fats, especially
butter, stick margarine, and meat fats, may offer numerous health
benefits.5 Olive oil and other oils rich in monounsaturated fatty
acids help to protect against heart disease by:
• Lowering total and LDL cholesterol and not lowering HDL
cholesterol or raising triglycerides6
• Lowering LDL cholesterol susceptibility to oxidation7
• Lowering blood-clotting factors8
• Providing phytochemicals that act as antioxidants (see High-
light 11)9
• Lowering blood pressure10
When compared with other fats, olive oil seems to be a wise
choice, but controlled clinical trials are too scarce to support popu-
lation-wide recommendations to switch to a high-fat diet rich in
olive oil. Importantly, olive oil is not a magic potion; drizzling it on
foods does not make them healthier. Like other fats, olive oil delivers
9 kcalories per gram, which can contribute to weight gain in people
who fail to balance their energy intake with their energy output. Its
role in a healthy diet is to replace the saturated fats. Other vegetable
oils, such as canola or safflower oil, are also generally low in satu-
rated fats and high in unsaturated fats. For this reason, heart-healthy
diets use these unsaturated vegetable oils as substitutes for the more
saturated fats of butter, hydrogenated stick margarine, lard, or
shortening. (Remember that the tropical oils—coconut, palm, and
palm kernel—are too saturated to be included with the heart-
healthy vegetable oils.)
Nibble on Nuts
Tree nuts and peanuts are traditionally excluded from low-fat di-
ets, and for good reasons. Nuts provide up to 80 percent of their
kcalories from fat, and a quarter cup (about an ounce) of mixed
nuts provides over 200 kcalories. In a recent review of the liter-
ature, however, researchers found that people who ate a one-
ounce serving of nuts on five or more days a week had a
reduced risk of heart disease compared with people who con-
sumed no nuts.11 A smaller positive association was noted for
any amount greater than one serving of nuts a week. The nuts
in this study were those commonly eaten in the United States:
almonds, Brazil nuts, cashews, hazelnuts, macadamia nuts,
pecans, pistachios, walnuts, and even peanuts. On average,
these nuts contain mostly monounsaturated fat (59 percent),
some polyunsaturated fat (27 percent), and little saturated fat
(14 percent).
Research has shown a benefit from walnuts and almonds in
particular. In study after study, walnuts, when substituted for
other fats in the diet, produce favorable effects on blood lipids—
even in people with elevated total and LDL cholesterol.12 Results
are similar for almonds. In one study, researchers gave men and
women one of three kinds of snacks, all of equal kcalories: whole-
wheat muffins, almonds (about 21/2 ounces), or half muffins and
half almonds.13 At the end of a month, people receiving the full
almond snack had the greatest drop in blood LDL cholesterol;
those eating the half almond snack had a lesser, but still signifi-
cant, drop in blood lipids; and those eating the muffin only snack
had no change.
Studies on peanuts, macadamia nuts, pecans, and pistachios
follow suit, indicating that including nuts may be a wise strategy
against heart disease. Nuts may protect against heart disease be-
cause they provide:
• Monounsaturated and polyunsaturated fats in abundance,
but few saturated fats
• Fiber, vegetable protein, and other valuable nutrients, in-
cluding the antioxidant vitamin E (see Highlight 11)
• Phytochemicals that act as antioxidants (see Highlight 13)
Before advising consumers to include nuts in their diets, a cau-
tion is in order. As mentioned, most of the energy nuts provide
comes from fats. Consequently, they deliver many kcalories per
bite. In studies examining the effects of nuts on heart disease, re-
searchers carefully adjust diets to make room for the nuts without
HIGH-FAT FOODS—FRIEND OR FOE? • 173
Olives and their oil may benefit heart health.
Matthew
Farruggio

increasing the total kcalories—that is, they use nuts instead of, not
in addition to, other foods (such as meats, potato chips, oils, mar-
garine, and butter). Consumers who do not make similar replace-
ments could end up gaining weight if they simply add nuts on
top of their regular diets. Weight gain, in turn, elevates blood
lipids and raises the risks of heart disease.
Feast on Fish
Research into the health benefits of the long-chain omega-3
polyunsaturated fatty acids began with a simple observation: the
native peoples of Alaska, northern Canada, and Greenland, who
eat a diet rich in omega-3 fatty acids, notably EPA and DHA, have
a remarkably low rate of heart disease even though their diets are
relatively high in fat.14 These omega-3 fatty acids help to protect
against heart disease by:15
• Reducing blood triglycerides
• Preventing blood clots
• Protecting against irregular heartbeats
• Lowering blood pressure
• Defending against inflammation
• Serving as precursors to eicosanoids
For people with hypertension or atherosclerosis, these actions can
be life saving.
Research studies have provided strong evidence that increas-
ing omega-3 fatty acids in the diet supports heart health and low-
ers the rate of deaths from heart disease.16 For this reason, the
American Heart Association recommends including fish in a
heart-healthy diet. People who eat some fish each week can lower
their risks of heart attack and stroke. Table 5-2 on p. 159 lists fish
that provide at least 1 gram of omega-3 fatty acids per serving.
Fish is the best source of EPA and DHA in the diet, but it is also a
major source of mercury, an environmental contaminant. Most fish
contain at least trace amounts of mercury, but tilefish (also known as
golden snapper or golden bass), swordfish, king mackerel, marlin,
and shark have especially high levels. For this reason, the FDA ad-
vises pregnant and lactating women, women of childbearing age
who may become pregnant, and young children to avoid:
• Tilefish (also called golden snapper or golden bass), sword-
fish, king mackeral, marlin, and shark
And to limit average weekly consumption of:
• A variety of fish and shellfish to 12 ounces (cooked or
canned)
• White (albacore) tuna to 6 ounces (cooked or canned)
Commonly eaten seafood relatively low in mercury include
shrimp, catfish, pollock, salmon, and canned light tuna.
In addition to the direct toxic effects of mercury, some (but
not all) research suggests that mercury may diminish the health
benefits of omega-3 fatty acids.17 Such findings serve as a re-
minder that our health depends on the health of our planet. The
protective effect of fish in the diet is available, provided that the
fish and their surrounding waters are not heavily contaminated.
In an effort to limit exposure to pollutants, some consumers
choose farm-raised fish. Compared with fish caught in the wild,
farm-raised fish tend to be lower in mercury, but they are also
lower in omega-3 fatty acids. When selecting fish, keep the diet
strategies of variety and moderation in mind. Varying choices and
eating moderate amounts helps to limit the intake of contami-
nants such as mercury.
174 • Highlight 5
For heart health, snack on a few nuts instead of potato chips.
Because nuts are energy dense (high in kcalories per ounce), it is
especially important to keep portion size in mind when eating
them.
Fish is a good source of the omega-3 fatty acids.
Matthew
Farruggio
©
www.comstock.com

High-Fat Foods and Heart
Disease
The number one dietary determinant of LDL cholesterol is satu-
rated fat. Figure H5-1 shows that each 1 percent increase in en-
ergy from saturated fatty acids in the diet may produce a 2
percent jump in heart disease risk by elevating blood LDL choles-
terol. Conversely, reducing saturated fat intake by 1 percent can
be expected to produce a 2 percent drop in heart disease risk by
the same mechanism. Even a 2 percent drop in LDL represents a
significant improvement for the health of the heart.18 Like satu-
rated fats, trans fats also raise heart disease risk by elevating LDL
cholesterol. A heart-healthy diet limits foods rich in these two
types of fat.
Limit Fatty Meats, Whole-Milk Products, and
Tropical Oils
The major sources of saturated fats in the U.S. diet are fatty
meats, whole milk products, tropical oils, and products made
from any of these foods. To limit saturated fat intake, consumers
must choose carefully among these high-fat foods. Over a third of
the fat in most meats is saturated. Similarly, over half of the fat is
saturated in whole milk and other high-fat dairy products, such as
cheese, butter, cream, half-and-half, cream cheese, sour cream,
and ice cream. The tropical oils of palm, palm kernel, and co-
conut, which are rarely used by consumers in the kitchen, are
used heavily by food manufacturers, and are commonly found in
many commercially prepared foods.
When choosing meats, milk products, and commercially pre-
pared foods, look for those lowest in saturated fat. Labels provide
a useful guide for comparing products in this regard, and Appen-
dix H lists the saturated fat in several thousand foods.
Even with careful selections, a nutritionally adequate diet will
provide some saturated fat. Zero saturated fat is not possible even
when experts design menus with the mission to keep saturated fat
as low as possible.19 Because most saturated fats come from ani-
mal foods, vegetarian diets can, and usually do, deliver fewer sat-
urated fats than mixed diets.
Limit Hydrogenated Foods
Chapter 5 explained that solid shortening and margarine are
made from vegetable oil that has been hardened through hydro-
genation. This process both saturates some of the unsaturated
fatty acids and introduces trans-fatty acids. Many convenience
foods contain trans fats, including:
• Fried foods such as French fries, chicken, and other com-
mercially fried foods
• Commercial baked goods such as cookies, doughnuts, pas-
tries, breads, and crackers
• Snack foods such as chips
• Imitation cheeses
To keep trans fat intake low, use these foods sparingly as an occa-
sional taste treat.
Table H5-1 (p. 176) summarizes which foods provide which fats.
Substituting unsaturated fats for saturated fats at each meal and
snack can help protect against heart disease. Figure H5-2 (p. 176)
compares two meals and shows how such substitutions can lower
saturated fat and raise unsaturated fat—even when total fat and
kcalories remain unchanged.
The Mediterranean Diet
The links between good health and traditional Mediterranean di-
ets of the mid-1900s were introduced earlier with regard to olive
2% decrease in
LDL cholesterolb
1% decrease in
dietary saturated
fatty acidsa
2% decrease in
heart disease riskc
1% increase in
dietary saturated
fatty acidsa
2% increase in
LDL cholesterolb
2% increase in
heart disease riskc
FIGURE H5-1 Potential Relationships among Dietary Saturated Fatty Acids, LDL Cholesterol, and Heart Disease Risk
aPercentage of change in total dietary energy from saturated fatty acids.
bPercentage of change in blood LDL cholesterol.
cPercentage of change in an individual’s risk of heart disease; the percentage of change in risk may increase when blood lipid changes are sustained over time.
SOURCE: Third Report of the National Cholesterol Education Program (NCEP) Expert Panel on Detection, Evaluation, and Treatment of High Blood Cholesterol in Adults (Adult Treatment Panel III), NIH publication no.
02-5215 (Bethesda, Md.: National Heart, Lung, and Blood Institute, 2002), p. V-8 and II-4.

176 •
TABLE H5-1 Major Sources of Various Fatty Acids
Healthful Fatty Acids
Monounsaturated Omega-6 Polyunsaturated Omega-3 Polyunsaturated
Avocado
Oils (canola, olive, peanut, sesame)
Nuts (almonds, cashews, filberts, hazelnuts,
macadamia nuts, peanuts, pecans, pistachios)
Olives
Peanut butter
Seeds (sesame)
Margarine (nonyhydrogenated)
Oils (corn, cottonseed, safflower, soybean)
Nuts (pine nuts, walnuts)
Mayonnaise
Salad dressing
Seeds (pumpkin, sunflower)
Fatty fish (herring, mackerel, salmon, tuna)
Flaxseed
Nuts (walnuts)
Harmful Fatty Acids
Saturated Trans
Bacon
Butter
Chocolate
Coconut
Cream cheese
Cream, half-and-half
Lard
Meat
Milk and milk products (whole)
Oils (coconut, palm, palm kernel)
Shortening
Sour cream
Fried foods (hydrogenated shortening)
Margarine (hydrogenated or partially
hydrogenated)
Nondairy creamers
Many fast foods
Shortening
Commercial baked goods (including doughnuts,
cakes, cookies)
Many snack foods (including microwave popcorn,
chips, crackers)
NOTE: Keep in mind that foods contain a mixture of fatty acids.
1 c fresh broccoli sautéed in
1 T olive oil
1 c mixed baby greens salad with
avocado
2 T sunflower seeds
4 oz grilled salmon
1
2
To lower saturated fat and
raise monounsaturated
and polyunsaturated fats...
1 c fresh broccoli topped with
1 T butter
1 c mixed baby greens salad with
2 strips bacon (crumbled)
1 oz blue cheese crumbles
4 oz grilled steak
Energy = 600 kcal
Energy = 600 kcal
UNSATURATED FATS MEAL
SATURATED FATS MEAL
10
10
0 20 30 50
40
Total fat
GRAMS
Saturated fat
Unsaturated fat
FIGURE H5-2 Two Meals Compared: Replacing Saturated Fat with Unsaturated Fat
Examples of ways to replace saturated fats with unsaturated fats include sautéing vegetables in olive oil instead of butter, garnishing
salads with avocado and sunflower seeds instead of bacon and blue cheese, and eating salmon instead of steak. Each of these meals
provides roughly the same number of kcalories and grams of fat, but the one on the left has almost four times as much saturated fat
and only half as many omega-3 fatty acids.
Highlight 5
Matthew
Farruggio
(both)

oil. For people who eat these diets, the incidence of heart disease,
some cancers, and other chronic diseases is low, and life ex-
pectancy is high.20
Although each of the many countries that border the Mediter-
ranean Sea has its own culture, traditions, and dietary habits,
their similarities are much greater than the use of olive oil alone.
In fact, according to a recent study, no one factor alone can be
credited with reducing disease risks—the association holds true
only when the overall diet pattern is present.21 Apparently, each
of the foods contributes small benefits that harmonize to produce
either a substantial cumulative or a synergistic effect.
The Mediterranean people focus their diets on crusty breads,
whole grains, potatoes, and pastas; a variety of vegetables
(including wild greens) and legumes; feta and mozzarella cheeses
and yogurt; nuts; and fruits (especially grapes and figs). They eat
some fish, other seafood, poultry, a few eggs, and little meat.
Along with olives and olive oil, their principal sources of fat are
nuts and fish; they rarely use butter or encounter hydrogenated
fats. Consequently, traditional Mediterranean diets are:
• Low in saturated fat
• Very low in trans fat
• Rich in unsaturated fat
• Rich in complex carbohydrate and fiber
• Rich in nutrients and phytochemicals that support good
health
People following the traditional Mediterranean diet can re-
ceive as much as 40 percent of a day’s kcalories from fat, but
their limited consumption of dairy products and meats provides
less than 10 percent from saturated fats. In addition, because the
animals in the Mediterranean region graze, the meat, dairy prod-
ucts, and eggs are richer in omega-3 fatty acids than those from
animals fed grain. Other foods typical of the Mediterranean,
such as wild plants and snails, provide omega-3 fatty acids as
well. All in all, the traditional Mediterranean diet has gained a
reputation for its health benefits as well as its delicious flavors,
but beware of the typical Mediterranean-style cuisine available in
U.S. restaurants. It has been adjusted to popular tastes, meaning
that it is often much higher in saturated fats and meats—and
much lower in the potentially beneficial constituents—than the
traditional fare. Unfortunately, it appears that people in the
Mediterranean region who are replacing some of their tradi-
tional dietary habits with those of the United States are losing
the health benefits previously enjoyed.22
Conclusion
Are some fats “good,” and others “bad” from the body’s point of
view? The saturated and trans fats indeed seem mostly bad for
the health of the heart. Aside from providing energy, which un-
saturated fats can do equally well, saturated and trans fats bring
no indispensable benefits to the body. Furthermore, no harm can
come from consuming diets low in them. Still, foods rich in these
fats are often delicious, giving them a special place in the diet.
In contrast, the unsaturated fats are mostly good for the health
of the heart when consumed in moderation. To date, their one
proven fault seems to be that they, like all fats, provide abundant
energy to the body and so may promote obesity if they drive
kcalorie intakes higher than energy needs.23 Obesity, in turn, of-
ten begets many body ills, as Chapter 8 makes clear.
When judging foods by their fatty acids, keep in mind that the
fat in foods is a mixture of “good” and “bad,” providing both sat-
urated and unsaturated fatty acids. Even predominantly monoun-
saturated olive oil delivers some saturated fat. Consequently, even
when a person chooses foods with mostly unsaturated fats, satu-
rated fat can still add up if total fat is high. For this reason, fat
must be kept below 35 percent of total kcalories if the diet is to be
moderate in saturated fat. Even experts run into difficulty when
attempting to create nutritious diets from a variety of foods that
are low in saturated fats when kcalories from fat exceed 35 per-
cent of the total.24
Does this mean that you must forever go without favorite
cheeses, ice cream cones, or a grilled steak? The famous chef Ju-
lia Child made this point about moderation:
An imaginary shelf labeled INDULGENCES is a good idea. It
contains the best butter, jumbo-size eggs, heavy cream,
marbled steaks, sausages and pâtés, hollandaise and butter
sauces, French butter-cream fillings, gooey chocolate
cakes, and all those lovely items that demand disciplined
rationing. Thus, with these items high up and almost out of
reach, we are ever conscious that they are not everyday
foods. They are for special occasions, and when that occa-
sion comes we can enjoy every mouthful.
Julia Child, The Way to Cook, 1989
Additionally, food manufacturers have come to the assistance
of consumers who wish to avoid the health threats from saturated
and trans fats. Some margarine makers no longer offer products
containing trans fats, and many snack manufacturers have re-
duced the saturated and trans fats in some products and now of-
fer snack foods in 100-kcalorie packages. Other companies are
following as consumers respond favorably.
Adopting some of the Mediterranean eating habits may
serve those who enjoy a little more fat in the diet. Including
vegetables, fruits, and legumes as part of a balanced daily diet is
a good idea, as is replacing saturated fats such as butter, short-
ening, and meat fat with unsaturated fats like olive oil and the
oils from nuts and fish. These foods provide vitamins, minerals,
and phytochemicals—all valuable in protecting the body’s
health. The authors of this book do not stop there, however.
They urge you to reduce fats from convenience foods and fast
foods; choose small portions of meats, fish, and poultry; and in-
clude fresh foods from all the food groups each day. Take care
to select portion sizes that will best meet your energy needs.
Also, exercise daily.

178 • Highlight 5
tion Program (NCEP) Expert Panel on Detec-
tion, Evaluation, and Treatment of High Blood
Cholesterol in Adults (Adult Treatment Panel
III), publication NIH no. 02-5215 (Bethesda,
Md.: National Heart, Lung, and Blood
Institute, 2002); Committee on Dietary
Reference Intakes, Dietary Reference Intakes
for Energy, Carbohydrate, Fiber, Fat, Fatty
Acids, Cholesterol, Protein, and Amino Acids
(Washington, D.C.: National Academies
Press, 2002/2005).
2002/2005, p. 769.
3. American Heart Association Scientific state-
ment: Diet and lifestyle recommendations
revision 2006, Circulation 114 (2006): 82–96;
Third Report of the National Cholesterol Educa-
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Md.: National Heart, Lung, and Blood
Institute, 2002); Committee on Dietary
for Energy, Carbohydrate, Fiber, Fat, Fatty
Acids, Cholesterol, Protein, and Amino Acids
(Washington, D.C.: National Academies
Press, 2002/2005).
4. A. Keys, Seven Countries: A Multivariate
Analysis of Death and Coronary Heart Disease
(Cambridge: Harvard University Press,
1980).
5. A. H. Stark and Z. Madar, Olive oil as a
functional food: Epidemiology and nutri-
tional approaches, Nutrition Reviews 60
(2002): 170–176.
6. M. I. Covas and coauthors, The effect of
polyphenols in olive oil on heart disease risk
factors, Annals of Internal Medicine 145
(2006): 333–341.
7. F. Visioli and coauthors, Virgin Olive Oil
Study (VOLOS): Vasoprotective potential of
extra virgin olive oil in mildly dislipidemic
patients, European Journal of Nutrition 44
(2005): 121–127.
8. J. López-Miranda, Monounsaturated fat and
cardiovascular risk, Nutrition Reviews 64
(2006): S2–S12.
9. F. Visioli and C. Galli, Biological properties
of olive oil phytochemicals, Critical Reviews
in Food Science and Nutrition 42 (2002):
209–221; M. N. Vissers and coauthors, Olive
oil phenols are absorbed in humans, Journal
of Nutrition 132 (2002): 409–417.
10. B. M. Rasmussen and coauthors, Effects of
dietary saturated, monounsaturated, and n-
3 fatty acids on blood pressure in healthy
subjects, American Journal of Clinical Nutri-
tion 83 (2006): 221–226; T. Psaltopoulou and
coauthors, Olive oil, the Mediterranean diet,
and arterial blood pressure: The Greek
European Prospective Investigation into
Cancer and Nutrition (EPIC) study, American
1012–1018.
11. J. H. Kelly and J. Sabate, Nuts and coronary
heart disease: An epidemiological perspec-
tive, British Journal of Nutrition 96 (2006):
S61–S67.
12. E. B. Feldman, The scientific evidence for a
beneficial health relationship between
walnuts and coronary heart disease, Journal
of Nutrition 132 (2002): 1062S–1101S.
13. D. J. Jenkins and coauthors, Dose response
of almonds on coronary heart disease risk
factors: Blood lipids, oxidized low-density
lipoproteins, lipoprotein (a), homocysteine,
and pulmonary nitric oxide: A randomized,
controlled, crossover trial, Circulation 106
(2002): 1327–1332.
14. E. Dewailly and coauthors, Cardiovascular
disease risk factors and n-3 fatty acid status
in the adult population of James Bay Cree,
(2002): 85–92.
15. J. L. Breslow, n-3 fatty acids and cardiovas-
cular disease, American Journal of Clinical
Nutrition 83 (2006): 1477S–1482S; P. J. H.
Jones and V. W. Y. Lau, Effect of n-3 polyun-
saturated fatty acids on risk reduction of
sudden death, Nutrition Reviews 60 (2002):
407–413.
16. Breslow, 2006; F. B. Hu and coauthors, Fish
and omega-3 fatty acid intake and risk of
coronary heart disease in women, Journal of
the American Medical Association 287 (2002):
1815–1821.
17. E. Guallar and coauthors, Mercury, fish oils,
and the risk of myocardial infarction, New
England Journal of Medicine 347 (2002):
1747–1754; K. Yoshizawa and coauthors,
Mercury and the risk of coronary heart
disease in man, New England Journal of
Medicine 347 (2002): 1755–1760.
III), 2002, p.V-8.
2002/2005, p. 835.
20. L. Serra-Majem, B. Roman, and R. Estruch,
Scientific evidence of interventions using
the Mediterranean diet: A systematic review,
Nutrition Reviews 64 (2006): S27–S47; C.
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REFERENCES

Their versatility in the body is impressive. They help your muscles to contract,
your blood to clot, and your eyes to see. They keep you alive and well by
facilitating chemical reactions and defending against infections. Without
them, your bones, skin, and hair would have no structure. No wonder they
were named proteins, meaning “of prime importance.” Does that mean
proteins deserve top billing in your diet as well? Are the best sources of
protein beef, beans, or broccoli? Learn which foods will supply you with
enough, but not too much, high-quality protein.
The CengageNOW logo
Figure 6.6: Animated! Protein Digestion in the
GI Tract
Figure 6.7: Animated! Protein Synthesis
Figure 6.10: Animated! An Example of a
Transport Protein
Russell Wasserfall/Getty Images

A few misconceptions surround the roles of protein in the body and the
importance of protein in the diet. For example, people who associate meat
with protein and protein with strength may eat steak to build muscles.
Their thinking is only partly correct, however. Protein is a vital structural
and working substance in all cells—not just muscle cells. To build strength,
muscles cells need physical activity and all the nutrients—not just protein.
Furthermore, protein is found in milk, eggs, legumes, and many grains
and vegetables—not just meat. By overvaluing protein and overemphasiz-
ing meat in the diet, a person may mistakenly crowd out other, equally im-
portant nutrients and foods. As this chapter describes the various roles of
protein in the body and food sources in the diet, keep in mind that protein
is one of many nutrients needed to maintain good health.
The Chemist’s View of Proteins
Chemically, proteins contain the same atoms as carbohydrates and lipids—carbon
(C), hydrogen (H), and oxygen (O)—but proteins also contain nitrogen (N) atoms.
These nitrogen atoms give the name amino (nitrogen containing) to the amino
acids—the links in the chains of proteins.
Amino Acids
All amino acids have the same basic structure—a central carbon (C) atom with a
hydrogen atom (H), an amino group (NH2), and an acid group (COOH) attached
to it. However, carbon atoms need to form four bonds, ◆ so a fourth attachment is
necessary. This fourth site distinguishes each amino acid from the others. Attached
to the carbon atom at the fourth bond is a distinct atom, or group of atoms, known
as the side group or side chain (see Figure 6-1).
Unique Side Groups The side groups on amino acids vary from one amino acid
to the next, making proteins more complex than either carbohydrates or lipids. A
polysaccharide (starch, for example) may be several thousand units long, but each
unit is a glucose molecule just like all the others. A protein, on the other hand, is
181
CHAPTER OUTLINE
The Chemist’s View of Proteins •
Amino Acids • Proteins
Digestion and Absorption of
Protein • Protein Digestion • Protein
Absorption
Proteins in the Body • Protein Synthe-
sis • Roles of Proteins • A Preview of Pro-
tein Metabolism
Protein in Foods • Protein Quality •
Protein Regulations for Food Labels
Intakes of Protein • Protein-Energy
Malnutrition • Health Effects of Protein •
Recommended Intakes of Protein •
Protein and Amino Acid Supplements
HIGHLIGHT 6 Nutritional Genomics
6
Protein: Amino
Acids
C H A P T E R
proteins: compounds composed of carbon,
hydrogen, oxygen, and nitrogen atoms,
arranged into amino acids linked in a chain.
Some amino acids also contain sulfur atoms.
amino (a-MEEN-oh) acids: building blocks of
proteins. Each contains an amino group, an
acid group, a hydrogen atom, and a
distinctive side group, all attached to a
central carbon atom.
• amino = containing nitrogen
◆ Reminder:
• H forms 1 bond
• O forms 2 bonds
• N forms 3 bonds
• C forms 4 bonds

182 • CHAPTER 6
made up of about 20 different amino acids, each with a different side group. Table
6-1 lists the amino acids most common in proteins.*
The simplest amino acid, glycine, has a hydrogen atom as its side group. A
slightly more complex amino acid, alanine, has an extra carbon with three hydro-
gen atoms. Other amino acids have more complex side groups (see Figure 6-2 for
examples). Thus, although all amino acids share a common structure, they differ
in size, shape, electrical charge, and other characteristics because of differences in
these side groups.
Nonessential Amino Acids More than half of the amino acids are nonessential,
meaning that the body can synthesize them for itself. Proteins in foods usually de-
liver these amino acids, but it is not essential that they do so. The body can make all
nonessential amino acids, given nitrogen to form the amino group and frag-
ments from carbohydrate or fat to form the rest of the structure.
FIGURE 6-1 Amino Acid Structure TABLE 6-1 Amino Acids
Proteins are made up of about 20 common amino acids. The first column lists the essential amino
acids for human beings (those the body cannot make—that must be provided in the diet). The
second column lists the nonessential amino acids. In special cases, some nonessential amino acids
may become conditionally essential (see the text). In a newborn, for example, only five amino
acids are truly nonessential; the other nonessential amino acids are conditionally essential until the
metabolic pathways are developed enough to make those amino acids in adequate amounts.
Essential Amino Acids Nonessential Amino Acids
Histidine (HISS-tuh-deen) Alanine (AL-ah-neen)
Isoleucine (eye-so-LOO-seen) Arginine (ARJ-ih-neen)
Leucine (LOO-seen) Asparagine (ah-SPAR-ah-geen)
Lysine (LYE-seen) Aspartic acid (ah-SPAR-tic acid)
Methionine (meh-THIGH-oh-neen) Cysteine (SIS-teh-een)
Phenylalanine (fen-il-AL-ah-neen) Glutamic acid (GLU-tam-ic acid)
Threonine (THREE-oh-neen) Glutamine (GLU-tah-meen)
Tryptophan (TRIP-toe-fan, Glycine (GLY-seen)
TRIP-toe-fane) Proline (PRO-leen)
Valine (VAY-leen) Serine (SEER-een)
Tyrosine (TIE-roe-seen)
FIGURE 6-2 Examples of Amino Acids
Note that all amino acids have a common chemical structure but that each has a
different side group. Appendix C presents the chemical structures of the 20 amino
acids most common in proteins.
* Besides the 20 common amino acids, which can all be components of proteins, others do not occur in
proteins, but can be found individually (for example, taurine and ornithine). Some amino acids occur
in related forms (for example, proline can acquire an OH group to become hydroxyproline).
nonessential amino acids: amino acids that
the body can synthesize (see Table 6-1).
H N
H H
C O H
C
O
Amino
group Acid
group
Side group
varies
H N
H H
C O H
O
C H N
H
C O H
O
C H N
H
C O H
O
C H N
H
C O H
O
C
H
H H H
C
H H
H
C
H H
C O H
C
H H
O
Glycine Alanine Aspartic acid Phenylalanine
All amino acids have a carbon (known as
the alpha-carbon), with an amino group
(NH2), an acid group (COOH), a hydrogen
(H), and a side group attached. The side
group is a unique chemical structure that
differentiates one amino acid from another.

PROTEIN: AMINO ACIDS • 183
Essential Amino Acids There are nine amino acids that the human body either
cannot make at all or cannot make in sufficient quantity to meet its needs. These
nine amino acids must be supplied by the diet; they are essential. ◆ The first column
in Table 6-1 presents the essential amino acids.
Conditionally Essential Amino Acids Sometimes a nonessential amino acid
becomes essential under special circumstances. For example, the body normally
uses the essential amino acid phenylalanine to make tyrosine (a nonessential
amino acid). But if the diet fails to supply enough phenylalanine, or if the body can-
not make the conversion for some reason (as happens in the inherited disease
phenylketonuria), then tyrosine becomes a conditionally essential amino acid.
Proteins
Cells link amino acids end-to-end in a variety of sequences to form thousands of dif-
ferent proteins. A peptide bond unites each amino acid to the next.
Amino Acid Chains Condensation reactions connect amino acids, just as they
combine monosaccharides to form disaccharides and fatty acids with glycerol to
form triglycerides. Two amino acids bonded together form a dipeptide (see Figure
6-3). By another such reaction, a third amino acid can be added to the chain to form
a tripeptide. As additional amino acids join the chain, a polypeptide is formed.
Most proteins are a few dozen to several hundred amino acids long. Figure 6-4
(p. 184) provides an example—insulin.
Amino Acid Sequences If a person could walk along a carbohydrate mole-
cule like starch, the first stepping stone would be a glucose. The next stepping
stone would also be a glucose, and it would be followed by a glucose, and yet
another glucose. But if a person were to walk along a polypeptide chain, each
stepping stone would be one of 20 different amino acids. The first stepping stone
might be the amino acid methionine. The second might be an alanine. The
third might be a glycine, and the fourth a tryptophan, and so on. Walking
along another polypeptide path, a person might step on a phenylalanine, then
a valine, and a glutamine. In other words, amino acid sequences within pro-
teins vary.
The amino acids can act somewhat like the letters in an alphabet. If you had
only the letter G, all you could write would be a string of Gs: G–G–G–G–G–G–G. But
with 20 different letters available, you can create poems, songs, and novels. Simi-
larly, the 20 amino acids can be linked together in a variety of sequences—even
more than are possible for letters in a word or words in a sentence. Thus the variety
of possible sequences for polypeptide chains is tremendous.
FIGURE 6-3 Condensation of Two Amino Acids to Form a Dipeptide
◆ Some researchers refer to essential amino
acids as indispensable and to nonessential
amino acids as dispensable.
essential amino acids: amino acids that the
body cannot synthesize in amounts sufficient
to meet physiological needs (see Table 6-1
on p. 182).
conditionally essential amino acid: an
amino acid that is normally nonessential, but
must be supplied by the diet in special
circumstances when the need for it exceeds
the body’s ability to produce it.
peptide bond: a bond that connects the acid
end of one amino acid with the amino end
of another, forming a link in a protein chain.
dipeptide (dye-PEP-tide): two amino acids
bonded together.
• di = two
• peptide = amino acid
tripeptide: three amino acids bonded
together.
• tri = three
polypeptide: many (ten or more) amino
acids bonded together.
• poly = many
H N
H
C O H
O
C
H
C
H H
H
N
H
C O H
O
C N
H
C O H
O
C
H H
C
H H C
H H
H
HOH
H N
H
C
O
C
H
C
H H
H
Amino acid
An OH group from the acid end of one amino
acid and an H atom from the amino group of
another join to form a molecule of water.
A peptide bond (highlighted in
red) forms between the two amino
acids, creating a dipeptide.
+ amino acid Dipeptide
Water

184 • CHAPTER 6
Protein Shapes Polypeptide chains twist into a variety of complex, tangled
shapes, depending on their amino acid sequences. The unique side group of
each amino acid gives it characteristics that attract it to, or repel it from, the
surrounding fluids and other amino acids. Some amino acid side groups
carry electrical charges that are attracted to water molecules; they are hy-
drophilic. Other side groups are neutral and are repelled by water; they are hy-
drophobic. As amino acids are strung together to make a polypeptide, the
chain folds so that its charged hydrophilic side groups are on the outer surface
near water; the neutral hydrophobic groups tuck themselves inside, away
from water. The intricate, coiled shape the polypeptide finally assumes gives it
maximum stability.
Protein Functions The extraordinary and unique shapes of proteins enable
them to perform their various tasks in the body. Some form hollow balls that
can carry and store materials within them, and some, such as those of ten-
dons, are more than ten times as long as they are wide, forming strong, rod-
like structures. Some polypeptides are functioning proteins just as they are;
others need to associate with other polypeptides to form larger working com-
plexes. Some proteins require minerals to activate them. One molecule of he-
moglobin—the large, globular protein molecule that, by the billions, packs
the red blood cells and carries oxygen—is made of four associated polypeptide
chains, each holding the mineral iron (see Figure 6-5).
Protein Denaturation When proteins are subjected to heat, acid, or other
conditions that disturb their stability, they undergo denaturation—that is,
they uncoil and lose their shapes and, consequently, also lose their ability to
function. Past a certain point, denaturation is irreversible. Familiar examples
FIGURE 6-4 Amino Acid Sequence of Human Insulin
Human insulin is a relatively small protein that consists of 51 amino acids in two
short polypeptide chains. (For amino acid abbreviations, see Appendix C.) Two
bridges link the two chains. A third bridge spans a section within the short chain.
Known as disulfide bridges, these links always involve the amino acid cysteine
(Cys), whose side group contains sulfur (S). Cysteines connect to each other when
bonds form between these side groups.
Chemically speaking, proteins are more complex than carbohydrates or
lipids, being made of some 20 different amino acids, 9 of which the body can-
not make; they are essential. Each amino acid contains an amino group, an
acid group, a hydrogen atom, and a distinctive side group, all attached to a
central carbon atom. Cells link amino acids together in a series of condensa-
tion reactions to create proteins. The distinctive sequence of amino acids in
each protein determines its unique shape and function.
IN SUMMARY
hemoglobin (HE-moh-GLO-bin): the
globular protein of the red blood cells that
carries oxygen from the lungs to the cells
throughout the body.
• hemo = blood
• globin = globular protein
denaturation (dee-NAY-chur-AY-shun): the
change in a protein’s shape and consequent
loss of its function brought about by heat,
agitation, acid, base, alcohol, heavy metals,
or other agents.
Cys Leu His Gln
Asn
Val
Phe
Gly
Ser
His
Leu
Val
Glu
Ala
Leu
Tyr
Leu
Val
Cys
Gly
Glu
Arg
Gly
Phe
Phe
Tyr
Thr
Pro Lys Ala
Cys Tyr Asn Glu Leu Gln Tyr Leu Ser Cys
Val
S
Asn
Gly Ile Val Glu Gln Cys Cys
Ala
Ser
S
S
S
S
S
Iron
Four highly folded polypeptide chains
form the globular hemoglobin protein.
Heme, the
nonprotein
portion of
hemoglobin,
holds iron.
The amino acid sequence
determines the shape
of the polypeptide chain.
FIGURE 6-5 The Structure of Hemoglobin

of denaturation include the hardening of an egg when it is cooked, the curdling of
milk when acid is added, and the stiffening of egg whites when they are whipped.
Digestion and Absorption of Protein
Proteins in foods do not become body proteins directly. Instead, they supply the
amino acids from which the body makes its own proteins. When a person eats foods
containing protein, enzymes break the long polypeptide strands into shorter
strands, the short strands into tripeptides and dipeptides, and, finally, the tripeptides
and dipeptides into amino acids.
Protein Digestion
Figure 6-6 (p. 186) illustrates the digestion of protein through the GI tract. Proteins
are crushed and moistened in the mouth, but the real action begins in the
stomach.
In the Stomach The major event in the stomach is the partial breakdown (hydrol-
ysis) of proteins. Hydrochloric acid uncoils (denatures) each protein’s tangled
strands so that digestive enzymes can attack the peptide bonds. The hydrochloric
acid also converts the inactive form ◆ of the enzyme pepsinogen to its active form,
pepsin. Pepsin cleaves proteins—large polypeptides—into smaller polypeptides
and some amino acids.
In the Small Intestine When polypeptides enter the small intestine, several pan-
creatic and intestinal proteases hydrolyze them further into short peptide chains,
◆ tripeptides, dipeptides, and amino acids. Then peptidase enzymes on the mem-
brane surfaces of the intestinal cells split most of the dipeptides and tripeptides into
single amino acids. Only a few peptides escape digestion and enter the blood intact.
Figure 6-6 includes names of the digestive enzymes for protein and describes their
actions.
Protein Absorption
A number of specific carriers transport amino acids (and some dipeptides and
tripeptides) into the intestinal cells. Once inside the intestinal cells, amino acids may
be used for energy or to synthesize needed compounds. Amino acids that are not
used by the intestinal cells are transported across the cell membrane into the sur-
rounding fluid where they enter the capillaries on their way to the liver.
Consumers lacking nutrition knowledge may fail to realize that most pro-
teins are broken down to amino acids before absorption. They may be mislead
by advertisements urging them to “Eat enzyme A. It will help you digest your
food.” Or “Don’t eat food B. It contains enzyme C, which will digest cells in
your body.” In reality, though, enzymes in foods are digested, just as all pro-
teins are. Even the digestive enzymes—which function optimally at their spe-
cific pH—are denatured and digested when the pH of their environment
changes. (For example, the enzyme pepsin, which works best in the low pH of
the stomach becomes inactive and digested when it enters the higher pH of the
small intestine.)
Another misconception is that eating predigested proteins (amino acid supple-
ments) saves the body from having to digest proteins and keeps the digestive sys-
tem from “overworking.” Such a belief grossly underestimates the body’s abilities.
As a matter of fact, the digestive system handles whole proteins better than predi-
gested ones because it dismantles and absorbs the amino acids at rates that are op-
timal for the body’s use. (The last section of this chapter discusses amino acid
supplements further.)
◆ The inactive form of an enzyme is called a
proenzyme or a zymogen (ZYE-moh-jen).
◆ A string of four to nine amino acids is an
oligopeptide (OL-ee-go-PEP-tide).
• oligo = few
pepsin: a gastric enzyme that hydrolyzes
protein. Pepsin is secreted in an inactive
form, pepsinogen, which is activated by
hydrochloric acid in the stomach.
proteases (PRO-tee-aces): enzymes that
hydrolyze protein.
peptidase: a digestive enzyme that
hydrolyzes peptide bonds. Tripeptidases
cleave tripeptides; dipeptidases cleave
dipeptides. Endopeptidases cleave peptide
bonds within the chain to create smaller
fragments, whereas exopeptidases cleave
bonds at the ends to release free amino
acids.
• tri = three
• di = two
• endo = within
• exo = outside

186 • CHAPTER 6
FIGURE 6-6 Animated! Protein Digestion in the GI Tract
PROTEIN
HYDROCHLORIC ACID
AND THE
DIGESTIVE ENZYMES
Mouth and salivary glands
Stomach
Chewing and crushing moisten
protein-rich foods and mix them with
saliva to be swallowed
Hydrochloric acid (HCl) uncoils protein
strands and activates stomach
enzymes:
Small intestine and pancreas
Pancreatic and small intestinal
enzymes split polypeptides further:
Then enzymes on the surface of the
small intestinal cells hydrolyze these
peptides and the cells absorb them:
Mouth
Salivary
glands
(Esophagus)
(Liver)
(Gallbladder)
Stomach
Pancreatic
duct
Pancreas
Small
intestine
Protein
pepsin,
HCI smaller
polypeptides
Peptides
intestinal
tripeptidases
and
dipeptidases amino acids
(absorbed)
Poly-
peptides
pancreatic
and
intestinal
proteases
tripeptides,
dipeptides,
amino acids
In the stomach:
Hydrochloric acid (HCl)
• Denatures protein structure
• Activates pepsinogen to pepsin
In the small intestine:
Enteropeptidasea
• Converts pancreatic trypsinogen
to trypsin
Pepsin
• Cleaves proteins to smaller
polypeptides and some free
amino acids
• Inhibits pepsinogen synthesis
a
Enteropeptidase was formerly known
as enterokinase.
Intestinal aminopeptidases
• Cleave amino acids from the
amino ends of small polypeptides
(oligopeptides)
Intestinal dipeptidases
• Cleave dipeptides to amino acids
Intestinal tripeptidases
• Cleave tripeptides to dipeptides
and amino acids
Elastase and collagenase
• Cleave polypeptides into smaller
polypeptides and tripeptides
Carboxypeptidases
• Cleave amino acids from the acid
(carboxyl) ends of polypeptides
Chymotrypsin
• Cleaves peptide bonds next to
the amino acids phenylalanine,
tyrosine, tryptophan, methionine,
asparagine, and histidine
Trypsin
• Inhibits trypsinogen synthesis
• Cleaves peptide bonds next to
the amino acids lysine and
arginine
• Converts pancreatic
procarboxypeptidases to
carboxypeptidases
• Converts pancreatic
chymotrypsinogen to
chymotrypsin
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Proteins in the Body
The human body contains an estimated 30,000 different kinds of proteins. Of
these, about 3000 have been studied, ◆ although with the recent surge in knowl-
edge gained from sequencing the human genome, ◆ this number is growing rap-
idly. Only about 10 are described in this chapter—but these should be enough to
illustrate the versatility, uniqueness, and importance of proteins. As you will see,
each protein has a specific function, and that function is determined during pro-
tein synthesis.
Protein Synthesis
Each human being is unique because of small differences in the body’s proteins.
These differences are determined by the amino acid sequences of proteins, which, in
turn, are determined by genes. The following paragraphs describe in words the ways
cells synthesize proteins; Figure 6-7 (p. 188) provides a pictorial description.
The instructions for making every protein in a person’s body are transmitted by
way of the genetic information received at conception. This body of knowledge,
which is filed in the DNA (deoxyribonucleic acid) within the nucleus of every cell,
never leaves the nucleus.
Delivering the Instructions Transforming the information in DNA into the ap-
propriate sequence of amino acids needed to make a specific protein requires two
major steps. In the first step, ◆ a stretch of DNA is used as a template to make a
strand of RNA (ribonucleic acid) known as messenger RNA. Messenger RNA then
carries the code across the nuclear membrane into the body of the cell. There it seeks
out and attaches itself to one of the ribosomes (a protein-making machine, which is
itself composed of RNA and protein), where the second step ◆ takes place. Situated
on a ribosome, messenger RNA specifies the sequence in which the amino acids line
up for the synthesis of a protein.
Lining Up the Amino Acids Other forms of RNA, called transfer RNA, collect
amino acids from the cell fluid and bring them to the messenger. Each of the 20
amino acids has a specific transfer RNA. Thousands of transfer RNAs, each carrying
its amino acid, cluster around the ribosomes, awaiting their turn to unload. When
the messenger’s list calls for a specific amino acid, the transfer RNA carrying that
amino acid moves into position. Then the next loaded transfer RNA moves into
place and then the next and the next. In this way, the amino acids line up in the se-
quence that is called for, and enzymes bind them together. Finally, the completed
protein strand is released, and the transfer RNAs are freed to return for other loads
of amino acids.
Sequencing Errors The sequence of amino acids in each protein determines its
shape, which supports a specific function. If a genetic error alters the amino acid se-
quence of a protein, or if a mistake is made in copying the sequence, an altered pro-
tein will result, sometimes with dramatic consequences. The protein hemoglobin
Digestion is facilitated mostly by the stomach’s acid and enzymes, which first
denature dietary proteins, then cleave them into smaller polypeptides and
some amino acids. Pancreatic and intestinal enzymes split these polypeptides
further, to oligo-, tri-, and dipeptides, and then split most of these to single
amino acids. Then carriers in the membranes of intestinal cells transport the
amino acids into the cells, where they are released into the bloodstream.
IN SUMMARY
◆ The study of the body’s proteins is called
proteomics.
◆ Reminder: The human genome is the full
set of chromosomes, including all of the
genes and associated DNA.
◆ This process of messenger RNA being
made from a template of DNA is known
as transcription.
◆ This process of messenger RNA directing
the sequence of amino acids and synthesis
of proteins is known as translation.

188 • CHAPTER 6
FIGURE 6-7 Animated! Protein Synthesis
1
2
4
5
6
3
Ribosomes
(protein-making
machinery)
mRNA
DNA
DNA Nucleus
Cell
The DNA serves as a template to make strands
of messenger RNA (mRNA). Each mRNA
strand copies exactly the instructions for
making some protein the cell needs.
The mRNA attaches itself to the protein-
making machinery of the cell, the
ribosomes.
Another form of RNA, transfer RNA (tRNA), collects
amino acids from the cell fluid. Each tRNA carries
its amino acids to the mRNA, which dictates the
sequence in which the amino acids will be
attached to form the protein strands. Thus the
mRNA ensures the amino acids are lined
up in the correct sequence.
The mRNA leaves
the nucleus through the
nuclear membrane. DNA
remains inside the nucleus.
Ribosome
mRNA
mRNA
Amino acid
tRNA
As the amino acids are lined up in the right
sequence, and the ribosome moves along
the mRNA, an enzyme bonds one amino
acid after another to the growing protein
strand. The tRNA are freed to return for
more amino acids. When all the amino
acids have been attached, the
completed protein is released.
Finally, the mRNA and ribosome separate. It takes
many words to describe these events, but in the cell,
40 to 100 amino acids can be added to a growing
protein strand in only a second. Furthermore several
ribosomes can simultaneously work on the same
mRNA to make many copies of the protein.
mRNA
Protein strand
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offers one example of such a genetic variation. In a
person with sickle-cell anemia, ◆ two of hemoglo-
bin’s four polypeptide chains (described earlier on p.
184) have the normal sequence of amino acids, but
the other two chains do not—they have the amino
acid valine in a position that is normally occupied by
glutamic acid (see Figure 6-8). This single alteration in
the amino acid sequence changes the characteristics
and shape of hemoglobin so much that it loses its abil-
ity to carry oxygen effectively. The red blood cells filled
with this abnormal hemoglobin stiffen into elongated
sickle, or crescent, shapes instead of maintaining their
normal pliable disc shape—hence the name, sickle-cell
anemia. Sickle-cell anemia raises energy needs, causes
many medical problems, and can be fatal.1 Caring for
children with sickle-cell anemia includes diligent at-
tention to their water needs; dehydration can trigger a
crisis.
Nutrients and Gene Expression When a cell
makes a protein as described earlier, scientists say that
the gene for that protein has been “expressed.” Cells
can regulate gene expression to make the type of
protein, in the amounts and at the rate, they need.
Nearly all of the body’s cells possess the genes for mak-
ing all human proteins, but each type of cell makes
only the proteins it needs. For example, cells of the
pancreas express the gene for insulin; in other cells,
that gene is idle. Similarly, the cells of the pancreas do
not make the protein hemoglobin, which is needed
only by the red blood cells.
Recent research has unveiled some of the fascinat-
ing ways nutrients regulate gene expression and pro-
tein synthesis (see Highlight 6). ◆ Because diet plays
an ongoing role in our lives from conception to death, it has a major influence
on gene expression and disease development.2 The benefits of polyunsaturated
fatty acids in defending against heart disease, for example, are partially ex-
plained by their role in influencing gene expression for lipid enzymes. Later
chapters provide additional examples of relationships among nutrients, genes,
and disease development.
FIGURE 6-8 Sickle Cell Compared with Normal Red Blood
Cell
Cells synthesize proteins according to the genetic information provided by the
DNA in the nucleus of each cell. This information dictates the order in which
amino acids must be linked together to form a given protein. Sequencing er-
rors occasionally occur, sometimes with significant consequences.
IN SUMMARY
Roles of Proteins
Whenever the body is growing, repairing, or replacing tissue, proteins are involved.
Sometimes their role is to facilitate or to regulate; other times it is to become part of
a structure. Versatility is a key feature of proteins.
sickle-cell anemia: a hereditary form of
anemia characterized by abnormal sickle- or
crescent-shaped red blood cells. Sickled cells
interfere with oxygen transport and blood
flow. Symptoms are precipitated by
dehydration and insufficient oxygen (as may
occur at high altitudes) and include hemolytic
anemia (red blood cells burst), fever, and
severe pain in the joints and abdomen.
gene expression: the process by which a cell
converts the genetic code into RNA and
protein.
◆ Anemia is not a disease, but a symptom of
various diseases. In the case of sickle-cell
anemia, a defect in the hemoglobin
molecule changes the shape of the red blood
cells. Later chapters describe the anemias of
vitamin and mineral deficiencies. In all
cases, the abnormal blood cells are unable to
meet the body’s oxygen demands.
◆ Nutrients can play key roles in activating or
silencing genes. Switching genes on and off,
without changing the genetic sequence itself,
is known as epigenetics.
• epi = among
Normally, red blood cells are disc-shaped, but in the inherited disor-
der sickle-cell anemia, red blood cells are sickle- or crescent-shaped.
This alteration in shape occurs because valine replaces glutamic
acid in the amino acid sequence of two of hemoglobin’s polypeptide
chains. As a result of this one alteration, the hemoglobin has a
diminished capacity to carry oxygen.
Amino acid sequence of sickle-cell hemoglobin:
Val His Leu Thr Pro Glu
Amino acid sequence of normal hemoglobin:
Val His Leu Thr Pro Glu
Glu
Val
Normal red blood cell
Sickle-shaped blood cell
PHOTO TO BE PLACED
©
Dr.
Stanley
Fiegler/Visuals
Unlimited

190 • CHAPTER 6
As Building Materials for Growth and
Maintenance From the moment of conception,
proteins form the building blocks of muscles,
blood, and skin—in fact, of most body structures.
For example, to build a bone or a tooth, cells first
lay down a matrix of the protein collagen and
then fill it with crystals of calcium, phosphorus,
magnesium, fluoride, and other minerals.
Collagen also provides the material of liga-
ments and tendons and the strengthening glue
between the cells of the artery walls that enables
the arteries to withstand the pressure of the blood
surging through them with each heartbeat. Also
made of collagen are scars that knit the sepa-
rated parts of torn tissues together.
Proteins are also needed for replacing dead
or damaged cells. The life span of a skin cell is
only about 30 days. As old skin cells are shed,
new cells made largely of protein grow from underneath to replace them. Cells
in the deeper skin layers synthesize new proteins to go into hair and fingernails.
Muscle cells make new proteins to grow larger and stronger in response to exer-
cise. Cells of the GI tract are replaced every few days. Both inside and outside,
then, the body continuously deposits protein into the new cells that replace
those that have been lost.
As Enzymes Some proteins act as enzymes. Digestive enzymes have appeared in
every chapter since Chapter 3, but digestion is only one of the many processes facil-
itated by enzymes. Enzymes not only break down substances, but they also build
substances (such as bone) ◆ and transform one substance into another (amino acids
into glucose, for example). Figure 6-9 diagrams a synthesis reaction.
An analogy may help to clarify the role of enzymes. Enzymes are comparable
to the clergy and judges who make and dissolve marriages. When a minister mar-
ries two people, they become a couple, with a new bond between them. They are
joined together—but the minister remains unchanged. The minister represents en-
zymes that synthesize large compounds from smaller ones. One minister can per-
form thousands of marriage ceremonies, just as one enzyme can perform billions
of synthetic reactions.
Similarly, a judge who lets married couples separate may decree many divorces
before retiring. The judge represents enzymes that hydrolyze larger compounds to
smaller ones; for example, the digestive enzymes. The point is that, like the minis-
ter and the judge, enzymes themselves are not altered by the reactions they facili-
tate. They are catalysts, permitting reactions to occur more quickly and efficiently
than if substances depended on chance encounters alone.
As Hormones The body’s many hormones are messenger molecules, and some
hormones are proteins. ◆ Various endocrine glands in the body release hormones in
response to changes that challenge the body. The blood carries the hormones from
these glands to their target tissues, where they elicit the appropriate responses to re-
store and maintain normal conditions.
The hormone insulin provides a familiar example. When blood glucose rises,
the pancreas releases its insulin. Insulin stimulates the transport proteins of the
muscles and adipose tissue to pump glucose into the cells faster than it can leak
out. (After acting on the message, the cells destroy the insulin.) Then, as blood glu-
cose falls, the pancreas slows its release of insulin. Many other proteins act as hor-
mones, regulating a variety of actions in the body (see Table 6-2 for examples).
As Regulators of Fluid Balance Proteins help to maintain the body’s fluid
balance. Figure 12-1 in Chapter 12 illustrates a cell and its associated fluids. As
the figure explains, the body’s fluids are contained inside the cells (intracellular)
The separate compounds,
A and B, are attracted to
the enzyme’s active site,
making a reaction likely.
The enzyme forms a
complex with A and B.
The enzyme is unchanged,
but A and B have formed
a new compound, AB.
New
compound
Enzyme Enzyme
A B
A B
Enzyme
A
B
FIGURE 6-9 Enzyme Action
Each enzyme facilitates a specific chemical reaction. In this diagram, an
enzyme enables two compounds to make a more complex structure, but
the enzyme itself remains unchanged.
matrix (MAY-tricks): the basic substance that
gives form to a developing structure; in the
body, the formative cells from which teeth and
bones grow.
collagen (KOL-ah-jen): the protein from which
connective tissues such as scars, tendons,
ligaments, and the foundations of bones and
teeth are made.
enzymes: proteins that facilitate chemical
reactions without being changed in the
process; protein catalysts.
fluid balance: maintenance of the proper
types and amounts of fluid in each
compartment of the body fluids (see
also Chapter 12).
◆ Breaking down reactions are catabolic,
whereas building up reactions are
anabolic. (Chapter 7 provides more
details.)
◆ Recall from Chapter 5 that some hormones,
such as estrogen and testosterone, derive
from cholesterol.

or outside the cells (extracellular). Extracellular fluids, in turn, can be found either
in the spaces between the cells (interstitial) or within the blood vessels (intravascu-
lar). The fluid within the intravascular spaces is called plasma (essentially blood
without its red blood cells). Fluids can flow freely between these compartments,
but being large, proteins cannot. Proteins are trapped primarily within the cells
and to a lesser extent in the plasma.
The exchange of materials between the blood and the cells takes place across the
capillary walls, which allow the passage of fluids and a variety of materials—but
usually not plasma proteins. Still some plasma proteins leak out of the capillaries
into the interstitial fluid between the cells. These proteins cannot be reabsorbed
back into the plasma; they normally reenter circulation via the lymph system. If
plasma proteins enter the interstitial spaces faster than they can be cleared, fluid
accumulates (because plasma proteins attract water) and causes swelling. Swelling
due to an excess of interstitial fluid is known as edema. The protein-related causes
of edema include:
• Excessive protein losses caused by kidney disease or large wounds (such as
extensive burns)
• Inadequate protein synthesis caused by liver disease
• Inadequate dietary intake of protein
Whatever the cause of edema, the result is the same: a diminished capacity to de-
liver nutrients and oxygen to the cells and to remove wastes from them. As a conse-
quence, cells fail to function adequately.
As Acid-Base Regulators Proteins also help to maintain the balance between
acids and bases within the body fluids. Normal body processes continually pro-
duce acids and bases, which the blood carries to the kidneys and lungs for excretion.
The challenge is to do this without upsetting the blood’s acid-base balance.
In an acid solution, hydrogen ions (H+) abound; the more hydrogen ions, the
more concentrated the acid. Proteins, which have negative charges on their sur-
faces, attract hydrogen ions, which have positive charges. By accepting and releas-
ing hydrogen ions, ◆ proteins maintain the acid-base balance of the blood and
body fluids.
The blood’s acid-base balance is tightly controlled. The extremes of acidosis
and alkalosis lead to coma and death, largely because they denature working
proteins. Disturbing a protein’s shape renders it useless. To give just one example,
denatured hemoglobin loses its capacity to carry oxygen.
As Transporters Some proteins move about in the body fluids, carrying nutrients
and other molecules. The protein hemoglobin carries oxygen from the lungs to the
cells. The lipoproteins transport lipids around the body. Special transport proteins
carry vitamins and minerals.
The transport of the mineral iron provides an especially good illustration of
these proteins’ specificity and precision. When iron enters an intestinal cell after a
meal has been digested and absorbed, it is captured by a protein. Before leaving
the intestinal cell, iron is attached to another protein that carries it though the
bloodstream to the cells. Once iron enters a cell, it is attached to a storage protein
that will hold the iron until it is needed. When it is needed, iron is incorporated
into proteins in the red blood cells and muscles that assist in oxygen transport and
use. (Chapter 13 provides more details on how these protein carriers transport and
store iron.)
Some transport proteins reside in cell membranes and act as “pumps,” picking
up compounds on one side of the membrane and releasing them on the other as
needed. Each transport protein is specific for a certain compound or group of re-
lated compounds. Figure 6-10 (p. 192) illustrates how a membrane-bound trans-
port protein helps to maintain the sodium and potassium concentrations in the
fluids inside and outside cells. The balance of these two minerals is critical to nerve
transmissions and muscle contractions; imbalances can cause irregular heartbeats,
muscular weakness, kidney failure, and even death.
◆ Compounds that help keep a solution’s acid-
ity or alkalinity constant are called buffers.
edema (eh-DEEM-uh): the swelling of body
tissue caused by excessive amounts of fluid
in the interstitial spaces; seen in protein
deficiency (among other conditions).
acids: compounds that release hydrogen ions
in a solution.
bases: compounds that accept hydrogen ions
in a solution.
acidosis (assi-DOE-sis): above-normal acidity
in the blood and body fluids.
alkalosis (alka-LOE-sis): above-normal
alkalinity (base) in the blood and body fluids.
TABLE 6-2 Examples of Hormones
and Their Actions
Hormones Actions
Growth hormone Promotes growth
Insulin and glucagon Regulate blood glucose
(see Chapter 4)
Thyroxin Regulates the body’s
metabolic rate
(see Chapter 8)
Calcitonin and Regulate blood calcium
parathyroid hormone (see Chapter 12)
Antidiuretic hormone Regulates fluid and
electrolyte balance
(see Chapter 12)
NOTE: Hormones are chemical messengers that are secreted by
endocrine glands in response to altered conditions in the body.
Each travels to one or more specific target tissues or organs, where
it elicits a specific response. For descriptions of many hormones
important in nutrition, see Appendix A.

192 • CHAPTER 6
As Antibodies Proteins also defend the body against disease. A virus—whether it
is one that causes flu, smallpox, measles, or the common cold—enters the cells and
multiplies there. One virus may produce 100 replicas of itself within an hour or so.
Each replica can then burst out and invade 100 different cells, soon yielding 10,000
virus particles, which invade 10,000 cells. Left free to do their worst, they will soon
overwhelm the body with disease.
Fortunately, when the body detects these invading antigens, it manufac-
tures antibodies, giant protein molecules designed specifically to combat
them. The antibodies work so swiftly and efficiently that in a normal, healthy
individual, most diseases never have a chance to get started. Without sufficient
protein, though, the body cannot maintain its army of antibodies to resist infec-
tious diseases.
Each antibody is designed to destroy a specific antigen. Once the body has man-
ufactured antibodies against a particular antigen (such as the measles virus), it “re-
members” how to make them. Consequently, the next time the body encounters
that same antigen, it produces antibodies even more quickly. In other words, the
body develops a molecular memory, known as immunity. (Chapter 15 describes
food allergies—the immune system’s response to food antigens.)
As a Source of Energy and Glucose Without energy, cells die; without glucose,
the brain and nervous system falter. Even though proteins are needed to do the work
that only they can perform, they will be sacrificed to provide energy ◆ and glucose ◆
during times of starvation or insufficient carbohydrate intake. The body will break
down its tissue proteins to make amino acids available for energy or glucose produc-
tion. In this way, protein can maintain blood glucose levels, but at the expense of los-
ing lean body tissue. Chapter 7 provides many more details on energy metabolism.
Other Roles As mentioned earlier, proteins form integral parts of most body struc-
tures such as skin, muscles, and bones. They also participate in some of the body’s
most amazing activities such as blood clotting and vision. When a tissue is injured,
a rapid chain of events leads to the production of fibrin, a stringy, insoluble mass of
protein fibers that forms a solid clot from liquid blood. Later, more slowly, the pro-
tein collagen forms a scar to replace the clot and permanently heal the wound. The
light-sensitive pigments in the cells of the eye’s retina are molecules of the protein
opsin. Opsin responds to light by changing its shape, thus initiating the nerve im-
pulses that convey the sense of sight to the brain.
◆ Reminder: Protein provides 4 kcal/g. Return
to p. 9 for a refresher on how to
calculate the protein kcalories from foods.
◆ Reminder: The making of glucose from non-
carbohydrate sources such as amino acids is
gluconeogenesis.
antigens: substances that elicit the formation
of antibodies or an inflammation reaction
from the immune system. A bacterium, a
virus, a toxin, and a protein in food that
causes allergy are all examples of antigens.
antibodies: large proteins of the blood and
body fluids, produced by the immune
system in response to the invasion of the
body by foreign molecules (usually proteins
called antigens). Antibodies combine with
and inactivate the foreign invaders, thus
protecting the body.
immunity: the body’s ability to defend itself
against diseases (see also Highlight 17).
Key:
The transport protein picks up
sodium from inside the cell.
The protein changes shape and
releases sodium outside the cell.
The protein changes shape and
releases potassium inside the
cell.
The transport protein picks up
potassium from outside the cell.
Outside
cell
Inside
cell
Cell
membrane
Potassium
Sodium
Transport
protein
FIGURE 6-10 Animated! An Example of a Transport Protein
This transport protein resides within a cell membrane and acts as a two-door passageway. Molecules enter on one side of the mem-
brane and exit on the other, but the protein doesn’t leave the membrane. This example shows how the transport protein moves
sodium and potassium in opposite directions across the membrane to maintain a high concentration of potassium and a low concen-
tration of sodium within the cell. This active transport system requires energy.

A Preview of Protein Metabolism
This section previews protein metabolism; Chapter 7 provides a full description.
Cells have several metabolic options, depending on their protein and energy needs.
Protein Turnover and the Amino Acid Pool Within each cell, proteins are
continually being made and broken down, a process known as protein turnover.
When proteins break down, they free amino acids. ◆ These amino acids mix with
amino acids from dietary protein to form an “amino acid pool” within the cells
and circulating blood. The rate of protein degradation and the amount of protein
intake may vary, but the pattern of amino acids within the pool remains fairly con-
stant. Regardless of their source, any of these amino acids can be used to make body
proteins or other nitrogen-containing compounds, or they can be stripped of their
nitrogen and used for energy (either immediately or stored as fat for later use).
Nitrogen Balance Protein turnover and nitrogen balance go hand in hand. In
healthy adults, protein synthesis balances with degradation, and protein intake from
food balances with nitrogen excretion in the urine, feces, and sweat. When nitrogen in-
take equals nitrogen output, the person is in nitrogen equilibrium, ◆ or zero nitrogen
balance. Researchers use nitrogen balance studies to estimate protein requirements.3
If the body synthesizes more than it degrades and adds protein, nitrogen status
becomes positive. Nitrogen status is positive in growing infants, children, adoles-
cents, pregnant women, and people recovering from protein deficiency or illness;
their nitrogen intake exceeds their nitrogen output. They are retaining protein in
new tissues as they add blood, bone, skin, and muscle cells to their bodies.
If the body degrades more than it synthesizes and loses protein, nitrogen status
becomes negative. Nitrogen status is negative in people who are starving or suffering
other severe stresses such as burns, injuries, infections, and fever; their nitrogen
Growing children end each day with more
bone, blood, muscle, and skin cells than they
had at the beginning of the day.
The protein functions discussed here are summarized in the accompanying table.
They are only a few of the many roles proteins play, but they convey some sense
of the immense variety of proteins and their importance in the body.
Growth and maintenance Proteins form integral parts of most body struc-
tures such as skin, tendons, membranes, mus-
cles, organs, and bones. As such, they support
the growth and repair of body tissues.
Enzymes Proteins facilitate chemical reactions.
Hormones Proteins regulate body processes. (Some, but
not all, hormones are proteins.)
Fluid balance Proteins help to maintain the volume and com-
position of body fluids.
Acid-base balance Proteins help maintain the acid-base balance of
body fluids by acting as buffers.
Transportation Proteins transport substances, such as lipids,
vitamins, minerals, and oxygen, around the
body.
Antibodies Proteins inactivate foreign invaders, thus
protecting the body against diseases.
Energy and glucose Proteins provide some fuel, and glucose if
needed, for the body’s energy needs.
IN SUMMARY
◆ Amino acids (or proteins) that derive from
within the body are endogenous (en-
DODGE-eh-nus). In contrast, those that de-
rive from foods are exogenous
(eks-ODGE-eh-nus).
• endo = within
• gen = arising
• exo = outside (the body)
◆ Nitrogen balance:
• Nitrogen equilibrium (zero nitrogen
balance): N in = N out.
• Positive nitrogen: N in N out.
• Negative nitrogen: N in N out.
protein turnover: the degradation and
synthesis of protein.
amino acid pool: the supply of amino acids
derived from either food proteins or body
proteins that collect in the cells and
circulating blood and stand ready to be
incorporated in proteins and other
compounds or used for energy.
nitrogen balance: the amount of nitrogen
consumed (N in) as compared with the
amount of nitrogen excreted (N out) in a
given period of time.*
©
Ariel
Skelley/Corbis
* The genetic materials DNA and RNA contain nitrogen, but the quantity is insignificant compared with
the amount in protein. Protein is 16 percent nitrogen. Said another way, the average protein weighs about
6.25 times as much as the nitrogen it contains, so scientists can estimate the amount of protein in a sample
of food, body tissue, or other material by multiplying the weight of the nitrogen in it by 6.25.

194 • CHAPTER 6
output exceeds their nitrogen intake. During these times, the body loses nitrogen as
it breaks down muscle and other body proteins for energy.
Using Amino Acids to Make Proteins or Nonessential Amino Acids As
mentioned, cells can assemble amino acids into the proteins they need to do their
work. If a particular nonessential amino acid is not readily available, cells can make
it from another amino acid. If an essential amino acid is missing, the body may
break down some of its own proteins to obtain it.
Using Amino Acids to Make Other Compounds Cells can also use amino acids
to make other compounds. For example, the amino acid tyrosine is used to make the
neurotransmitters norepinephrine and epinephrine, which relay nervous system
messages throughout the body. Tyrosine can also be made into the pigment melanin,
which is responsible for brown hair, eye, and skin color, or into the hormone thy-
roxin, which helps to regulate the metabolic rate. For another example, the amino
acid tryptophan serves as a precursor for the vitamin niacin and for serotonin, a neu-
rotransmitter important in sleep regulation, appetite control, and sensory perception.
Using Amino Acids for Energy and Glucose As mentioned earlier, when glu-
cose or fatty acids are limited, cells are forced to use amino acids for energy and glu-
cose. The body does not make a specialized storage form of protein as it does for
carbohydrate and fat. Glucose is stored as glycogen in the liver and fat as triglyc-
erides in adipose tissue, but protein in the body is available only from the working
and structural components of the tissues. When the need arises, the body breaks
down its tissue proteins and uses their amino acids for energy or glucose. Thus, over
time, energy deprivation (starvation) always causes wasting of lean body tissue as
well as fat loss. An adequate supply of carbohydrates and fats spares amino acids
from being used for energy and allows them to perform their unique roles.
Deaminating Amino Acids When amino acids are broken down (as occurs
when they are used for energy), they are first deaminated—stripped of their nitro-
gen-containing amino groups. Deamination produces ammonia, which the cells
release into the bloodstream. The liver picks up the ammonia, converts it into urea
(a less toxic compound), and returns the urea to the blood. The production of urea
increases as dietary protein increases, until production hits its maximum rate at in-
takes approaching 250 grams per day. (Urea metabolism is described in Chapter 7.)
The kidneys filter urea out of the blood; thus the amino nitrogen ends up in the
urine. The remaining carbon fragments of the deaminated amino acids may enter
a number of metabolic pathways—for example, they may be used for energy or for
the production of glucose, ketones, cholesterol, or fat.*
Using Amino Acids to Make Fat Amino acids may be used to make fat when en-
ergy and protein intakes exceed needs and carbohydrate intake is adequate. The
amino acids are deaminated, the nitrogen is excreted, and the remaining carbon
fragments are converted to fat and stored for later use. In this way, protein-rich foods
can contribute to weight gain.
Proteins are constantly being synthesized and broken down as needed. The
body’s assimilation of amino acids into proteins and its release of amino acids
via protein degradation and excretion can be tracked by measuring nitrogen
balance, which should be positive during growth and steady in adulthood. An
energy deficit or an inadequate protein intake may force the body to use
amino acids as fuel, creating a negative nitrogen balance. Protein eaten in ex-
cess of need is degraded and stored as body fat.
IN SUMMARY
* Chemists sometimes classify amino acids according to the destinations of their carbon fragments after
deamination. If the fragment leads to the production of glucose, the amino acid is called glucogenic; if it
leads to the formation of ketone bodies, fats, and sterols, the amino acid is called ketogenic. There is no
sharp distinction between glucogenic and ketogenic amino acids, however. A few are both, most are
considered glucogenic, only one (leucine) is clearly ketogenic.
neurotransmitters: chemicals that are
released at the end of a nerve cell when a
nerve impulse arrives there. They diffuse
across the gap to the next cell and alter the
membrane of that second cell to either
inhibit or excite it.
deamination (dee-AM-ih-NAY-shun):
removal of the amino (NH2) group from a
compound such as an amino acid.

Protein in Foods
In the United States and Canada, where nutritious foods are abundant, most people
eat protein in such large quantities that they receive all the amino acids they need.
In countries where food is scarce and the people eat only marginal amounts of pro-
tein-rich foods, however, the quality of the protein becomes crucial.
Protein Quality
The protein quality of the diet determines, in large part, how well children grow and
how well adults maintain their health. Put simply, high-quality proteins provide
enough of all the essential amino acids needed to support the body’s work, and low-
quality proteins don’t. Two factors influence protein quality—the protein’s digestibil-
ity and its amino acid composition.
Digestibility As explained earlier, proteins must be digested before they can pro-
vide amino acids. Protein digestibility depends on such factors as the protein’s
source and the other foods eaten with it. The digestibility of most animal proteins is
high (90 to 99 percent); plant proteins are less digestible (70 to 90 percent for most,
but over 90 percent for soy and legumes).
Amino Acid Composition To make proteins, a cell must have all the needed
amino acids available simultaneously. The liver can produce any nonessential
amino acid that may be in short supply so that the cells can continue linking amino
acids into protein strands. If an essential amino acid is missing, though, a cell must
dismantle its own proteins to obtain it. Therefore, to prevent protein breakdown, di-
etary protein must supply at least the nine essential amino acids plus enough nitro-
gen-containing amino groups and energy for the synthesis of the others. If the diet
supplies too little of any essential amino acid, protein synthesis will be limited. The
body makes whole proteins only; if one amino acid is missing, the others cannot
form a “partial” protein. An essential amino acid supplied in less than the amount
needed to support protein synthesis is called a limiting amino acid.
Reference Protein The quality of a food protein is determined by comparing its
amino acid composition with the essential amino acid requirements of preschool-
age children. Such a standard is called a reference protein. ◆ The rationale be-
hind using the requirements of this age group is that if a protein will effectively
support a young child’s growth and development, then it will meet or exceed the re-
quirements of older children and adults.
High-Quality Proteins As mentioned earlier, a high-quality protein contains all
the essential amino acids in relatively the same amounts and proportions that hu-
man beings require; it may or may not contain all the nonessential amino acids.
Proteins that are low in an essential amino acid cannot, by themselves, support pro-
tein synthesis. Generally, foods derived from animals (meat, fish, poultry, cheese,
eggs, yogurt, and milk) provide high-quality proteins, although gelatin is an excep-
tion. (It lacks tryptophan and cannot support growth and health as a diet’s sole pro-
tein.) Proteins from plants (vegetables, nuts, seeds, grains, and legumes) have more
diverse amino acid patterns and tend to be limiting in one or more essential amino
acids. Some plant proteins are notoriously low quality (for example, corn protein).
A few others are high quality (for example, soy protein).
Researchers have developed several methods for evaluating the quality of food
proteins and identifying high-quality proteins. Appendix D provides details.
Complementary Proteins In general, plant proteins are lower quality than an-
imal proteins, and plants also offer less protein (per weight or measure of food). For
this reason, many vegetarians improve the quality of proteins in their diets by com-
bining plant-protein foods that have different but complementary amino acid pat-
terns. This strategy yields complementary proteins that together contain all the
◆ In the past, egg protein was commonly used
as the reference protein. Table D-1 in Appen-
dix D presents the amino acid profile of egg.
As the reference protein, egg was assigned
the value of 100; Table D-3 includes scores of
other food proteins for comparison.
high-quality proteins: dietary proteins
containing all the essential amino acids in
relatively the same amounts that human
beings require. They may also contain
nonessential amino acids.
protein digestibility: a measure of the
amount of amino acids absorbed from a
given protein intake.
limiting amino acid: the essential amino
acid found in the shortest supply relative to
the amounts needed for protein synthesis in
the body. Four amino acids are most likely to
be limiting:
• Lysine
• Methionine
• Threonine
• Tryptophan
reference protein: a standard against which
to measure the quality of other proteins.
complementary proteins: two or more
dietary proteins whose amino acid
assortments complement each other in such
a way that the essential amino acids missing
from one are supplied by the other.
Black beans and rice, a favorite Hispanic com-
bination, together provide a balanced array of
amino acids.
©
Polara
Studios
Inc.

196 • CHAPTER 6
essential amino acids in quantities sufficient to support health. The protein quality
of the combination is greater than for either food alone (see Figure 6-11).
Many people have long believed that combining plant proteins at every meal
is critical to protein nutrition. For most healthy vegetarians, though, it is not nec-
essary to balance amino acids at each meal if protein intake is varied and energy
intake is sufficient.4 Vegetarians can receive all the amino acids they need over the
course of a day by eating a variety of whole grains, legumes, seeds, nuts, and veg-
etables. Protein deficiency will develop, however, when fruits and certain vegeta-
bles make up the core of the diet, severely limiting both the quantity and quality of
protein. Highlight 2 describes how to plan a nutritious vegetarian diet.
FIGURE 6-11 Complementary Proteins
A diet that supplies all of the essential amino acids in adequate amounts en-
sures protein synthesis. The best guarantee of amino acid adequacy is to eat
foods containing high-quality proteins or mixtures of foods containing com-
plementary proteins that can each supply the amino acids missing in the
other. In addition to its amino acid content, the quality of protein is measured
by its digestibility and its ability to support growth. Such measures are of great
importance in dealing with malnutrition worldwide, but in the United States
and Canada, where protein deficiency is not common, protein quality scores
of individual foods deserve little emphasis.
IN SUMMARY
Protein Regulations for Food Labels
All food labels must state the quantity of protein in grams. The “% Daily Value”
◆ for protein is not mandatory on all labels but is required whenever a food makes
a protein claim or is intended for consumption by children under four years old.*
Whenever the Daily Value percentage is declared, researchers must determine the
quality of the protein. Thus, when a % Daily Value is stated for protein, it reflects
both quantity and quality.
Intakes of Protein
As you know by now, protein is indispensable to life. It should come as no surprise
that protein deficiency can have devastating effects on people’s health. But, like the
other nutrients, protein in excess can also be harmful. This section examines the
health effects and recommended intakes of protein.
Protein-Energy Malnutrition
When people are deprived of protein, energy, or both, the result is protein-energy
malnutrition (PEM). Although PEM touches many adult lives, it most often strikes
early in childhood. It is one of the most prevalent and devastating forms of malnu-
trition in the world, afflicting one of every four children worldwide. Most of the
33,000 children who die each day are malnourished.5
Inadequate food intake leads to poor growth in children and to weight loss and
wasting in adults. Children who are thin for their height may be suffering from
* For labeling purposes, the Daily Values for protein are as follows: for infants, 14 grams; for children
under age four, 16 grams; for older children and adults, 50 grams; for pregnant women, 60 grams; and
for lactating women, 65 grams.
Lys Met Trp
Legumes
Grains
Together
Ile
In general, legumes provide plenty of
isoleucine (Ile) and lysine (Lys) but fall
short in methionine (Met) and trypto-
phan (Trp). Grains have the opposite
strengths and weaknesses, making them
a perfect match for legumes.
protein-energy malnutrition (PEM), also
called protein-kcalorie malnutrition
(PCM): a deficiency of protein, energy, or
both, including kwashiorkor, marasmus, and
instances in which they overlap (see p. 198).
◆ Daily Value:
• 50 g protein (based on 10% of 2000
kcal diet)
Donated food saves some people from starva-
tion, but it is usually insufficient to meet nutri-
ent needs or even to defend against hunger.
AP/Wide
World
Photos

acute PEM (recent severe food deprivation), whereas children who are short for
their age have experienced chronic PEM (long-term food deprivation). Poor
growth due to PEM is easy to overlook because a small child may look quite nor-
mal, but it is the most common sign of malnutrition.
PEM is most prevalent in Africa, Central America, South America, and East and
Southeast Asia. In the United States, homeless people and those living in substandard
housing in inner cities and rural areas have been diagnosed with PEM. In addition to
those living in poverty, elderly people who live alone and adults who are addicted to
drugs and alcohol are frequently victims of PEM. PEM can develop in young children
when parents mistakenly provide “health-food beverages” ◆ that lack adequate en-
ergy or protein instead of milk, most commonly because of nutritional ignorance,
perceived milk intolerance, or food faddism. Adult PEM is also seen in people hospi-
talized with infections such as AIDS or tuberculosis; these infections deplete body pro-
teins, demand extra energy, induce nutrient losses, and alter metabolic pathways.
Furthermore, poor nutrient intake during hospitalization worsens malnutrition and
impairs recovery, whereas nutrition intervention often improves the body’s response
to other treatments and the chances of survival. PEM is also common in those suffer-
ing from the eating disorder anorexia nervosa (discussed in Highlight 8). Prevention
emphasizes frequent, nutrient-dense, energy-dense meals and, equally important,
resolution of the underlying causes of PEM—poverty, infections, and illness.
Classifying PEM PEM occurs in two forms: marasmus and kwashiorkor, which
differ in their clinical features (see Table 6-3). The following paragraphs present
three clinical syndromes—marasmus, kwashiorkor, and the combination of the two.
Marasmus Appropriately named from the Greek word meaning “dying away,”
marasmus reflects a severe deprivation of food over a long time (chronic PEM).
Put simply, the person is starving and suffering from an inadequate energy and
protein intake (and inadequate essential fatty acids, vitamins, and minerals as well).
Marasmus occurs most commonly in children from 6 to 18 months of age in all the
overpopulated and impoverished areas of the world. Children in impoverished
nations simply do not have enough to eat and subsist on diluted cereal drinks that
supply scant energy and protein of low quality; such food can barely sustain life,
much less support growth. Consequently, marasmic children look like little old peo-
ple—just skin and bones.
◆ Rice drinks are often sold as milk alternatives,
but they fail to provide adequate protein, vita-
mins, and minerals.
TABLE 6-3 Features of Marasmus and Kwashiorkor in Children
Separating PEM into two classifications oversimplifies the condition, but at the extremes, marasmus and kwashiorkor exhibit marked differences. Marasmus-
kwashiorkor mix presents symptoms common to both marasmus and kwashiorkor. In all cases, children are likely to develop diarrhea, infections, and multi-
ple nutrient deficiencies.
Marasmus Kwashiorkor
Infancy (less than 2 yr) Older infants and young children (1 to 3 yr)
Severe deprivation, or impaired absorption, of protein, energy, Inadequate protein intake or, more commonly, infections
vitamins, and minerals
Develops slowly; chronic PEM Rapid onset; acute PEM
Severe weight loss Some weight loss
Severe muscle wasting, with no body fat Some muscle wasting, with retention of some body fat
Growth: 60% weight-for-age Growth: 60 to 80% weight-for-age
No detectable edema Edema
No fatty liver Enlarged fatty liver
Anxiety, apathy Apathy, misery, irritability, sadness
Good appetite possible Loss of appetite
Hair is sparse, thin, and dry; easily pulled out Hair is dry and brittle; easily pulled out; changes color; becomes straight
Skin is dry, thin, and easily wrinkles Skin develops lesions
acute PEM: protein-energy malnutrition
caused by recent severe food restriction;
characterized in children by thinness for
height (wasting).
chronic PEM: protein-energy malnutrition
caused by long-term food deprivation;
characterized in children by short height for
age (stunting).
marasmus (ma-RAZ-mus): a form of PEM
that results from a severe deprivation, or
impaired absorption, of energy, protein,
vitamins, and minerals.

198 • CHAPTER 6
Without adequate nutrition, muscles, including the heart, waste and weaken.
Because the brain normally grows to almost its full adult size within the first two
years of life, marasmus impairs brain development and learning ability. Reduced
synthesis of key hormones slows metabolism and lowers body temperature. There
is little or no fat under the skin to insulate against cold. Hospital workers find that
children with marasmus need to be clothed, covered, and kept warm. Because these
children often suffer delays in their mental and behavioral development, they also
need loving care, a stimulating environment, and parental attention.
The starving child faces this threat to life by engaging in as little activity as pos-
sible—not even crying for food. The body musters all its forces to meet the crisis, so
it cuts down on any expenditure of energy not needed for the functioning of the
heart, lungs, and brain. Growth ceases; the child is no larger at age four than at
age two. Enzymes are in short supply and the GI tract lining deteriorates. Conse-
quently, the child can’t digest and absorb what little food is eaten.
Kwashiorkor Kwashiorkor typically reflects a sudden and recent deprivation
of food (acute PEM). Kwashiorkor is a Ghanaian word that refers to the birth posi-
tion of a child and is used to describe the illness a child develops when the next
child is born. When a mother who has been nursing her first child bears a second
child, she weans the first child and puts the second one on the breast. The first
child, suddenly switched from nutrient-dense, protein-rich breast milk to a
starchy, protein-poor cereal, soon begins to sicken and die. Kwashiorkor typically
sets in between 18 months and two years.
Kwashiorkor usually develops rapidly as a result of protein deficiency or, more
commonly, is precipitated by an illness such as measles or other infection. Other
factors, such as aflatoxins (a contaminant sometimes found in moldy grains), may
also contribute to the development of, or symptoms that accompany, kwashiorkor.6
The loss of weight and body fat is usually not as severe in kwashiorkor as in
marasmus, but some muscle wasting may occur. Proteins and hormones that pre-
viously maintained fluid balance diminish, and fluid leaks into the interstitial
spaces. The child’s limbs and abdomen become swollen with edema, a distinguish-
ing feature of kwashiorkor. ◆ A fatty liver develops due to a lack of the protein car-
riers that transport fat out of the liver. The fatty liver lacks enzymes to clear
metabolic toxins from the body, so their harmful effects are prolonged. Inflamma-
tion in response to these toxins and to infections further contributes to the edema
that accompanies kwashiorkor. Without sufficient tyrosine to make melanin, the
child’s hair loses its color, and inadequate protein synthesis leaves the skin patchy
and scaly, often with sores that fail to heal. The lack of proteins to carry or store
iron leaves iron free. Unbound iron is common in children with kwashiorkor and
may contribute to their illnesses and deaths by promoting bacterial growth and
free-radical damage. (Free-radical damage is discussed fully in Highlight 11.)
Marasmus-Kwashiorkor Mix The combination of marasmus and kwashiorkor
is characterized by the edema of kwashiorkor with the wasting of marasmus. Most
often, the child suffers the effects of both malnutrition and infections. Some re-
searchers believe that kwashiorkor and marasmus are two stages of the same dis-
ease. They point out that kwashiorkor and marasmus often exist side by side in the
same community where children consume the same diet. They note that a child
who has marasmus can later develop kwashiorkor. Some research indicates that
marasmus represents the body’s adaptation to starvation and that kwashiorkor de-
velops when adaptation fails.
Infections In PEM, antibodies to fight off invading bacteria are degraded to pro-
vide amino acids for other uses, leaving the malnourished child vulnerable to in-
fections. Blood proteins, including hemoglobin, are no longer synthesized, so the
child becomes anemic and weak. Dysentery, an infection of the digestive tract,
causes diarrhea, further depleting the body of nutrients and fluids. In the maras-
mic child, once infection sets in, kwashiorkor often follows, and the immune re-
sponse weakens further.7
The extreme loss of muscle and fat characteris-
tic of marasmus is apparent in this child’s
“matchstick” arms.
◆ For this reason, kwashiorkor is sometimes
referred to as “wet” PEM and marasmus as
“dry” PEM.
AP/Wide
World
Photos
kwashiorkor (kwash-ee-OR-core, kwash-ee-
or-CORE): a form of PEM that results either
from inadequate protein intake or, more
commonly, from infections.
dysentery (DISS-en-terry): an infection of the
digestive tract that causes diarrhea.

The combination of infections, fever, fluid imbalances, and anemia often leads
to heart failure and occasionally sudden death. Infections combined with malnu-
trition are responsible for two-thirds of the deaths of young children in developing
countries. Measles, which might make a healthy child sick for a week or two, kills
a child with PEM within two or three days.
Rehabilitation If caught in time, the life of a starving child may be saved with nu-
trition intervention. In severe cases, diarrhea will have incurred dramatic fluid and
mineral losses that need to be replaced during the first 24 to 48 hours to help raise
the blood pressure and strengthen the heartbeat. After that, protein and food energy
may be given in small quantities, with intakes gradually increased as tolerated. Se-
verely malnourished people, especially those with edema, recover better with an ini-
tial diet that is relatively low in protein (10 percent kcalories from protein).
Experts assure us that we possess the knowledge, technology, and resources to
end hunger. Programs that tailor interventions to the local people and involve them
in the process of identifying problems and devising solutions have the most success.
To win the war on hunger, those who have the food, technology, and resources must
make fighting hunger a priority (see Highlight 16 for more on hunger).
Health Effects of Protein
While many of the world’s people struggle to obtain enough food energy and pro-
tein, in developed countries both are so abundant that problems of excess are
seen. Overconsumption of protein offers no benefits and may pose health risks.
High-protein diets have been implicated in several chronic diseases, including
heart disease, cancer, osteoporosis, obesity, and kidney stones, but evidence is in-
sufficient to establish an upper level.8
Researchers attempting to clarify the relationships between excess protein and
chronic diseases face several obstacles. Population studies have difficulty determin-
ing whether diseases correlate with animal proteins or with their accompanying
saturated fats, for example. Studies that rely on data from vegetarians must sort
out the many lifestyle factors, in addition to a “no-meat diet,” that might explain
relationships between protein and health.
Heart Disease A high-protein diet may contribute to the progression of heart dis-
ease. As Chapter 5 mentioned, foods rich in animal protein also tend to be rich in
saturated fats. Consequently, it is not surprising to find a correlation between ani-
mal-protein intake (red meats and dairy products) and heart disease.9 On the other
hand, substituting vegetable protein for animal protein improves blood lipids and
decreases heart disease mortality.10
Research suggests that elevated levels of the amino acid homocysteine may be
an independent risk factor for heart disease, heart attacks, and sudden death in
patients with heart disease.11 Researchers do not yet fully understand the many
factors—including a high protein diet—that can raise homocysteine in the blood
or whether elevated levels are a cause or an effect of heart disease.12 Until they can
determine the exact role homocysteine plays in heart disease, researchers are fol-
lowing several leads in pursuit of the answers. Coffee’s role in heart disease has
been controversial, but research suggests it is among the most influential factors
in raising homocysteine, which may explain some of the adverse health effects of
heavy consumption.13 Elevated homocysteine levels are among the many adverse
health consequences of smoking cigarettes and drinking alcohol as well.14 Homo-
cysteine is also elevated with inadequate intakes of B vitamins and can usually be
lowered with fortified foods or supplements of vitamin B12, vitamin B6, and fo-
late.15 Lowering homocysteine, however, may not help in preventing heart at-
tacks.16 Supplements of the B vitamins do not always benefit those with heart
disease and in fact, may actually increase the risks.17
In contrast to homocysteine, the amino acid arginine may help protect against
heart disease by lowering blood pressure and homocysteine levels.18 Additional
research is needed to confirm the benefits of arginine.19 In the meantime, it is unwise
The edema characteristic of kwashiorkor is
apparent in this child’s swollen belly. Malnour-
ished children commonly have an enlarged
abdomen from parasites as well.
©
Paul
A.
Sounders/Corbis

200 • CHAPTER 6
for consumers to use supplements of arginine, or any other amino acid for that
matter (as pp. 202–203 explain). Physicians, however, may find it beneficial to
add arginine supplements to their heart patients’ treatment plan.20
Cancer As in heart disease, the effects of protein and fats on cancers cannot be eas-
ily separated. Population studies suggest a correlation between high intakes of ani-
mal proteins and some types of cancer (notably, cancer of the colon, breast, kidneys,
pancreas, and prostate).
Adult Bone Loss (Osteoporosis) Chapter 12 presents calcium metabolism, and
Highlight 12 elaborates on the main factors that influence osteoporosis. This section
briefly describes the relationships between protein intake and bone loss. When pro-
tein intake is high, calcium excretion increases. Whether excess protein depletes the
bones of their chief mineral may depend upon the ratio of calcium intake to protein
intake. After all, bones need both protein and calcium. An ideal ratio has not been de-
termined, but a young woman whose intake meets recommendations for both nutri-
ents has a calcium-to-protein ratio of more than 20 to 1 (milligrams to grams), which
probably provides adequate protection for the bones. For most women in the United
States, however, average calcium intakes are lower and protein intakes are higher,
yielding a 9-to-1 ratio, which may produce calcium losses significant enough to com-
promise bone health. In other words, the problem may reflect too little calcium, not
too much protein.21 In establishing recommendations, the DRI Committee considered
protein’s effect on calcium metabolism and bone health, but it did not find sufficient
evidence to warrant an adjustment for calcium or an upper level for protein.22
Some (but not all) research suggests that animal protein may be more detrimen-
tal to calcium metabolism and bone health than vegetable protein.23 A review of
the topic, however, concludes that excess protein—whether from animal or veg-
etable sources—increases calcium excretion and, perhaps more importantly, that
the other nutrients in the protein source may be equally, if not more, responsible for
the effects on bone health.24
Inadequate intakes of protein may also compromise bone health.25 Osteoporo-
sis is particularly common in elderly women and in adolescents with anorexia ner-
vosa—groups who typically receive less protein than they need. For these people,
increasing protein intake may be just what they need to protect their bones.26
Weight Control Dietary protein may play a role in increasing body weight.27 Pro-
tein-rich foods are often fat-rich foods that contribute to weight gain with its accom-
panying health risks. As Highlight 9 explains, weight-loss gimmicks that encourage
a high-protein, low-carbohydrate diet may be temporarily effective, but only be-
cause they are low-kcalorie diets. Diets that provide adequate protein, moderate fat,
and sufficient energy from carbohydrates can better support weight loss and good
health. Including protein at each meal may help with weight loss by providing sati-
ety.28 Selecting too many protein-rich foods, such as meat and milk, may crowd out
fruits, vegetables, and whole grains, making the diet inadequate in other nutrients.
Kidney Disease Excretion of the end products of protein metabolism depends,
in part, on an adequate fluid intake and healthy kidneys. A high protein intake
increases the work of the kidneys, but does not appear to diminish kidney function
or cause kidney disease.29 Restricting dietary protein, however, may help to slow
the progression of kidney disease and limit the formation of kidney stones in peo-
ple who have these conditions.
Protein deficiencies arise from both energy-poor and protein-poor diets and lead to
the devastating diseases of marasmus and kwashiorkor. Together, these diseases
are known as PEM (protein-energy malnutrition), a major form of malnutrition
causing death in children worldwide. Excesses of protein offer no advantage; in
fact, overconsumption of protein-rich foods may incur health problems as well.
IN SUMMARY

Recommended Intakes of Protein
As mentioned earlier, the body continuously breaks down and loses some protein
and cannot store amino acids. To replace protein, the body needs dietary protein
for two reasons. First, food protein is the only source of the essential amino acids,
and second, it is the only practical source of nitrogen with which to build the
nonessential amino acids and other nitrogen-containing compounds the body
needs.
Given recommendations that people’s fat intakes should contribute 20 to 35
percent of total food energy and carbohydrate intakes should contribute 45 to 65
percent, that leaves 10 to 35 percent for protein. In a 2000-kcalorie diet, that repre-
sents 200 to 700 kcalories from protein, or 50 to 175 grams. Average intakes in the
United States and Canada fall within this range.
Protein RDA The protein RDA ◆ for adults is 0.8 grams per kilogram of healthy
body weight per day. For infants and children, the RDA is slightly higher. The
table on the inside front cover lists the RDA for males and females at various ages
in two ways—grams per day based on reference body weights and grams per kilo-
gram body weight per day.
The RDA generously covers the needs for replacing worn-out tissue, so it in-
creases for larger people; it also covers the needs for building new tissue during
growth, so it increases for infants, children, and pregnant women. The protein RDA
is the same for athletes as for others, although some fitness authorities recommend
a slightly higher intake.30 The accompanying “How to” explains how to calculate
your RDA for protein.
In setting the RDA, the DRI Committee assumes that people are healthy and do
not have unusual metabolic needs for protein, that the protein eaten will be of
mixed quality (from both high- and low-quality sources), and that the body will
use the protein efficiently. In addition, the committee assumes that the protein is
consumed along with sufficient carbohydrate and fat to provide adequate energy
and that other nutrients in the diet are adequate.
Adequate Energy Note the qualification “adequate energy” in the preceding
statement, and consider what happens if energy intake falls short of needs. An in-
take of 50 grams of protein provides 200 kcalories, which represents 10 percent of
the total energy from protein, if the person receives 2000 kcalories a day. But if the
person cuts energy intake drastically—to, say, 800 kcalories a day—then an intake
of 200 kcalories from protein is suddenly 25 percent of the total; yet it’s still the same
amount of protein (number of grams). The protein intake is reasonable, but the en-
ergy intake is not. The low energy intake forces the body to use the protein to meet
energy needs rather than to replace lost body protein. Similarly, if the person’s en-
ergy intake is high—say, 4000 kcalories—the 50-gram protein intake represents only
5 percent of the total; yet it still is a reasonable protein intake. Again, the energy in-
take is unreasonable for most people, but in this case, it permits the protein to be
used to meet the body’s needs.
Be careful when judging protein (or carbohydrate or fat) intake as a percentage
of energy. Always ascertain the number of grams as well, and compare it with the
RDA or another standard stated in grams. A recommendation stated as a percent-
age of energy intake is useful only if the energy intake is within reason.
Protein in Abundance Most people in the United States and Canada receive
more protein than they need. Even athletes in training typically don’t need to in-
crease their protein intakes because the additional foods they eat to meet their high
energy needs deliver protein as well. That protein intake is high is not surprising
considering the abundance of food eaten and the central role meats hold in the
North American diet. A single ounce of meat (or 1/2 cup legumes) delivers about 7
grams of protein, so 8 ounces of meat alone supplies more than the RDA for an av-
erage-size person. Besides meat, well-fed people eat many other nutritious foods,
many of which also provide protein. A cup of milk provides 8 grams of protein.
To figure your protein RDA:
• Look up the healthy weight for a person of
your height (inside back cover). If your
present weight falls within that range, use it
for the following calculations. If your pres-
ent weight falls outside the range, use the
midpoint of the healthy weight range as
your reference weight.
• Convert pounds to kilograms, if necessary
(pounds divided by 2.2 equals kilograms).
• Multiply kilograms by 0.8 to get your RDA
in grams per day. (Older teens 14 to 18
years old, multiply by 0.85.) Example:
Weight 150 lb
150 lb 2.2 lb/kg 68 kg (rounded off)
68 kg 0.8 g/kg 54 g protein (rounded off)
HOW TO Calculate Recommended
Protein Intakes
◆ RDA for protein:
• 0.8 g/kg/day
• 10 to 35% of energy intake
For many people, this 5-ounce steak provides
almost all of the meat and much of the pro-
tein recommended for a day’s intake.
©
Polara
Studios,
Inc.
To calculate recommended protein intakes, log on to
academic.cengage.com/login, go to Chapter 6, then
go to How To.

202 • CHAPTER 6
Grains and vegetables provide small amounts of protein, but they can add up to sig-
nificant quantities; fruits and fats provide no protein.
To illustrate how easy it is to overconsume protein, consider the amounts recom-
mended by the USDA Food Guide for a 2000-kcalorie diet. Six ounces of grains pro-
vide about 18 grams of protein; 21/2 cups of vegetables deliver about 10 grams; 3
cups of milk offer 24 grams; and 51/2 ounces of meat supply 38 grams. This totals
90 grams of protein—higher than recommendations for most people and yet still
lower than the average intake of people in the United States.
People in the United States and Canada get more protein than they need. If they
have an adequate food intake, they have a more-than-adequate protein intake.
The key diet-planning principle to emphasize for protein is moderation. Even
though most people receive plenty of protein, some feel compelled to take supple-
ments as well, as the next section describes.
The optimal diet is adequate in energy from carbohydrate and fat and deliv-
ers 0.8 grams of protein per kilogram of healthy body weight each day. U.S.
and Canadian diets are typically more than adequate in this respect.
IN SUMMARY
Protein and Amino Acid Supplements
Websites, health-food stores, and popular magazine articles advertise a wide variety
of protein supplements, and people take these supplements for many different rea-
sons. Athletes take protein powders to build muscle. Dieters take them to spare their
bodies’ protein while losing weight. Women take them to strengthen their finger-
nails. People take individual amino acids, too—to cure herpes, to make themselves
sleep better, to lose weight, and to relieve pain and depression.* Like many other
magic solutions to health problems, protein and amino acid ◆ supplements don’t
work these miracles. Furthermore, they may be harmful.
Protein Powders Because the body builds muscle protein from amino acids, many
athletes take protein powders with the false hope of stimulating muscle growth. Mus-
cle work builds muscle; protein supplements do not, and athletes do not need them.
Taking protein supplements does not improve athletic performance.31 Protein powders
can supply amino acids to the body, but nature’s protein sources—lean meat, milk,
eggs, and legumes—supply all these amino acids and more.
Whey protein appears to be particularly popular among athletes hoping to
achieve greater muscle gains. A waste product of cheese manufacturing, whey
protein is a common ingredient in many low-cost protein powders. When com-
bined with strength training, whey supplements may increase protein synthesis
slightly, but they do not seem to enhance athletic performance.32 To build
stronger muscles, athletes need to eat food with adequate energy and protein to
support the weight-training work that does increase muscle mass. Those who still
think they need more whey should pour a glass of milk; one cup provides 1.5
grams of whey.
Purified protein preparations contain none of the other nutrients needed to sup-
port the building of muscle, and the protein they supply is not needed by athletes
who eat food. It is excess protein, and the body dismantles it and uses it for energy
or stores it as body fat. The deamination of excess amino acids places an extra bur-
den on the kidneys to excrete unused nitrogen.
Amino Acid Supplements Single amino acids do not occur naturally in foods
and offer no benefit to the body; in fact, they may be harmful. The body was not de-
signed to handle the high concentrations and unusual combinations of amino acids
◆ Use of amino acids as dietary supplements is
inappropriate, especially for:
• All women of childbearing age
• Pregnant or lactating women
• Infants, children, and adolescents
• Elderly people
• People with inborn errors of metabolism
that affect their bodies’ handling of
amino acids
• Smokers
• People on low-protein diets
• People with chronic or acute mental or
physical illnesses who take amino acids
without medical supervision
* Canada only allows single amino acid supplements to be sold as drugs or used as food additives.
whey protein: a by-product of cheese
production; falsely promoted as increasing
muscle mass. Whey is the watery part of milk
that separates from the curds.
Vegetarians obtain their protein from whole
grains, legumes, nuts, vegetables, and, in some
cases, eggs and milk products.
©
Polara
Studios
Inc.

found in supplements. An excess of one amino acid can create such a demand for a
carrier that it limits the absorption of another amino acid, presenting the possibility
of a deficiency. Those amino acids winning the competition enter in excess, creating
the possibility of toxicity. Toxicity of single amino acids in animal studies raises con-
cerns about their use in human beings. Anyone considering taking amino acid sup-
plements should check with a registered dietitian or physician first.
Most healthy athletes eating well-balanced diets do not need amino acid sup-
plements. Advertisers point to research that identifies the branched-chain
amino acids ◆ as the main ones used as fuel by exercising muscles. What the
ads leave out is that compared to glucose and fatty acids, branched-chain amino
acids provide very little fuel and that ordinary foods provide them in abundance
anyway. Large doses of branched-chain amino acids can raise plasma ammonia
concentrations, which can be toxic to the brain. Branched-chain amino acid sup-
plements may be useful in conditions such as advanced liver failure, but other-
wise, they are not routinely recommended.33
In two cases, recommendations for single amino acid supplements have led to
widespread public use—lysine to prevent or relieve the infections that cause herpes
cold sores on the mouth or genital organs, and tryptophan to relieve pain, depres-
sion, and insomnia. In both cases, enthusiastic popular reports preceded careful
scientific experiments and health recommendations. Research is insuffiencient to
determine whether lysine suppresses herpes infections, but it appears safe (up to 3
grams per day) when taken in divided doses with meals.34
Tryptophan may be effective with respect to pain and sleep, but its use for these
purposes is experimental. About 20 years ago, more than 1500 people who elected
to take tryptophan supplements developed a rare blood disorder known as
eosinophilia-myalgia syndrome (EMS). EMS is characterized by severe muscle and
joint pain, extremely high fever, and, in over three dozen cases, death. Treatment
for EMS usually involves physical therapy and low doses of corticosteroids to relieve
symptoms temporarily. The Food and Drug Administration implicated impurities
in the supplements, issued a recall of all products containing manufactured trypto-
phan, and warned that high-dose supplements of tryptophan might provoke EMS
even in the absence of impurities.
Normal, healthy people never need protein or amino acid supplements. It is
safest to obtain lysine, tryptophan, and all other amino acids from protein-rich
foods, eaten with abundant carbohydrate and some fat to facilitate their use in
the body. With all that we know about science, it is hard to improve on nature.
◆ The branched-chain amino acids are leucine,
isoleucine, and valine.
Foods that derive from animals—meats, fish, poultry, eggs, and milk products—provide
plenty of protein but are often accompanied by fat. Those that derive from plants—
whole grains, vegetables, and legumes—may provide less protein but also less fat.
■ Calculate your daily protein needs and compare them with your protein intake.
Consider whether you receive enough, but not too much, protein daily.
■ Describe your dietary sources of proteins and whether you use mostly plant-based
or animal-based protein foods in your diet.
■ Debate the risks and benefits of taking protein or amino acid supplements.
branched-chain amino acids: the essential
amino acids leucine, isoleucine, and valine,
which are present in large amounts in
skeletal muscle tissue; falsely promoted as
fuel for exercising muscles.
IN SUMMARY

204 • CHAPTER 6
• Learn more about sickle-cell anemia from the National
Heart, Lung, and Blood Institute or the Sickle Cell Disease
Association of America: www.nhlbi.nih.gov
or www.sicklecelldisease.org
• Learn more about protein-energy malnutrition and world
hunger from the World Health Organization Nutrition
Programme or the National Institute of Child Health and
Human Development: www.who.int/nut or
www.nichd.nih.gov
• Highlight 16 offers many more websites on malnutrition
and world hunger.
nutrition-related calculations using hypothetical situations
(see p. 206 for answers). Once you have mastered these
examples, you will be prepared to examine your own protein
needs. Be sure to show your calculations for each problem.
1. Compute recommended protein intakes for people of
different sizes. Refer to the “How to” on p. 201 and
compute the protein recommendation for the following
people. The intake for a woman who weighs 144 pounds
is computed for you as an example.
144 lb 2.2 lb/kg 65 kg
0.8 g/kg 65 kg 52 g protein per day
a. a woman who weighs 116 pounds
b. a man (18 years) who weighs 180 pounds
For additional practice, log on to academic.cengage.com/login. Go to Chapter 6, then to Nutrition Calculations.
2. The chapter warns that recommendations based on
percentage of energy intake are not always appropriate.
Consider a woman 26 years old who weighs 165 pounds.
Her diet provides 1500 kcalories/day with 50 grams
carbohydrate and 100 grams fat.
a. What is this woman’s protein intake? Show your
calculations.
b. Is her protein intake appropriate? Justify your
answer.
c. Are her carbohydrate and fat intakes appropriate?
Justify your answer.
This exercise should help you develop a perspective on
protein recommendations.
These questions will help you review the chapter. You will
1. How does the chemical structure of proteins differ from
the structures of carbohydrates and fats? (pp. 181–184)
2. Describe the structure of amino acids, and explain how
their sequence in proteins affects the proteins’ shapes.
What are essential amino acids? (pp. 181–184)
3. Describe protein digestion and absorption. (pp. 185–186)
4. Describe protein synthesis. (pp. 187–189)
5. Describe some of the roles proteins play in the human
body. (pp. 189–192)
6. What are enzymes? What roles do they play in chemical
reactions? Describe the differences between enzymes and
hormones. (p. 190)
7. How does the body use amino acids? What is deamina-
tion? Define nitrogen balance. What conditions are
associated with zero, positive, and negative balance?
(pp. 193–194)
8. What factors affect the quality of dietary protein? What
is a high-quality protein? (pp. 195–196)
9. How can vegetarians meet their protein needs without
eating meat? (pp. 195–196)
10. What are the health consequences of ingesting inade-
quate protein and energy? Describe marasmus and
kwashiorkor. How can the two conditions be
distinguished, and in what ways do they overlap?
(pp. 196–199)
11. How might protein excess, or the type of protein eaten,
influence health? (pp. 199–200)
12. What factors are considered in establishing
recommended protein intakes? (pp. 201–202)
13. What are the benefits and risks of taking protein and
amino acid supplements? (p. 202–203)
STUDY QUESTIONS

1. Which part of its chemical structure differentiates one
amino acid from another?
a. its side group
b. its acid group
c. its amino group
d. its double bonds
2. Isoleucine, leucine, and lysine are:
a. proteases.
b. polypeptides.
c. essential amino acids.
d. complementary proteins.
3. In the stomach, hydrochloric acid:
a. denatures proteins and activates pepsin.
b. hydrolyzes proteins and denatures pepsin.
c. emulsifies proteins and releases peptidase.
d. condenses proteins and facilitates digestion.
4. Proteins that facilitate chemical reactions are:
a. buffers.
b. enzymes.
c. hormones.
d. antigens.
5. If an essential amino acid that is needed to make a
protein is unavailable, the cells must:
a. deaminate another amino acid.
b. substitute a similar amino acid.
c. break down proteins to obtain it.
d. synthesize the amino acid from glucose and nitrogen.
6. Protein turnover describes the amount of protein:
a. found in foods and the body.
b. absorbed from the diet.
c. synthesized and degraded.
d. used to make glucose.
7. Which of the following foods provides the highest qual-
ity protein?
a. egg
b. corn
c. gelatin
d. whole grains
8. Marasmus develops from:
a. too much fat clogging the liver.
b. megadoses of amino acid supplements.
c. inadequate protein and energy intake.
d. excessive fluid intake causing edema.
9. The protein RDA for a healthy adult who weighs 180
pounds is:
a. 50 milligrams/day.
b. 65 grams/day.
c. 180 grams/day.
d. 2000 milligrams/day.
10. Which of these foods has the least protein per 1/2 cup?
a. rice
b. broccoli
c. pinto beans
d. orange juice
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women need dietary protein to maintain
bone mass, Nutrition Reviews 60 (2002):
337–341; M. T. Munoz and J. Argente,
Anorexia nervosa in female adolescents:
Endocrine and bone mineral density distur-
bances, European Journal of Endocrinology 147
(2002): 275–286.
27. A. Trichopoulou and coauthors, Lipid,
protein and carbohydrate intake in relation
to body mass index, European Journal of
28. A. Astrup, The satiating power of protein—a
key to obesity prevention? American Journal
of Clinical Nutrition 82 (2005): 1–2; D. S.
Weigle and coauthors, A high-protein diet
induces sustained reductions in appetite, ad
libitum caloric intake, and body weight
despite compensatory changes in diurnal
plasma leptin and ghrelin concentrations,
(2005): 41–48.
29. E. L. Knight and coauthors, The impact of
protein intake on renal function decline in
women with normal renal function or mild
renal insufficiency, Annals of Internal Medi-
cine 138 (2003): 460–467.
tion, Dietitians of Canada, and the Ameri-
can College of Sports Nutrition, Nutrition
and athletic performance, Journal of the
1543–1556.
31. L. L. Andersen and coauthors, The effect of
resistance training combined with timed
ingestion of protein on muscle fiber size and
muscle strength, Metabolism: Clinical and
Experimental 54 (2005): 151–156.
32. K. D. Tipton, Ingestion of casein and whey
proteins result in muscle anabolism after
resistance exercise, Medicine and Science in
Sports and Exercise 36 (2004): 2073–2081.
33. R. Mascarenhas and S. Mobarhan, New
support for branched-chain amino acid
supplementation in advanced hepatic
failure, Nutrition Reviews 62 (2004): 33–38.
34. M. M. Perfect and coauthors, Use of com-
plementary and alternative medicine for the
treatment of genital herpes, Herpes 12
(2005): 38–41.
1. a. 116 lb 2.2 lb/kg 53 kg
b. 180 lb 2.2 lb/kg 82 kg
He is 18 years old, so use 0.85 g/kg.
2. a. 50 g carbohydrate 4 kcal/g 200 kcal from carbohydrate
100 g fat 9 kcal/g 900 kcal from fat
1500 kcal (200 900 kcal) 400 kcal from protein
400 kcal 4 kcal/g 100 g protein
b. Using the RDA guideline of 0.8 g/kg, an appropriate protein
intake for this woman would be 60 g protein/day (165 lb
2.2 lb/kg 75 kg; 0.8 g/kg 75 60 g/day). Her intake
is higher than her RDA. Using the guideline that protein
should contribute 10 to 35% of energy intake, her intake of
100 g protein on a 1500 kcal diet falls within the suggested
range (400 kcal protein 1500 total kcal 27%).
c. Using the guideline that carbohydrate should contribute 45
to 65% and fat should contribute 20 to 35% of energy
intake, her intake of 50 g carbohydrate is low (200 kcal car-
bohydrate 1500 total kcal 13%), and her intake of
100 g fat is high (900 kcal fat 1500 total kcal 60%).
1. a 2. c 3. a 4. b 5. c 6. c 7. a
8. c 9. b 10. d
ANSWERS

HIGHLIGHT 6
207
Imagine this scenario: A physician scrapes a
sample of cells from inside your cheek and
submits it to a genomics lab. The lab re-
turns a report based on your genetic profile
that reveals which diseases you are most
likely to develop and makes recommenda-
tions for specific diet and lifestyle changes
that can help you maintain good health. You
may also be given a prescription for a dietary supplement that
will best meet your personal nutrient requirements. Such a sce-
nario may one day become reality as scientists uncover the ge-
netic relationships between diet and disease. (Until then,
however, consumers need to know that current genetic test kits
commonly available on the Internet are unproven and quite
likely fraudulent.)
How nutrients influence gene activity and how genes influ-
ence the activities of nutrients is the focus of a new field of study
called nutritional genomics (see the accompanying glossary).
Unlike sciences in the 20th century, nutritional genomics takes a
comprehensive approach in analyzing information from several
fields of study, providing an integrated understanding of the find-
ings.1 Consider how multiple disciplines contributed to our un-
derstanding of vitamin A over the past several decades, for
example. Biochemistry revealed vitamin A’s three chemical struc-
tures. Immunology identified the anti-infective properties of one
of these structures while physiology focused
on another structure and it’s role in vision.
Epidemiology has reported improvements
in the death rates and vision of malnour-
ished children given vitamin A supple-
ments, and biology has explored how such
effects might be possible. The process was
slow as researchers collected information on
one gene, one action, and one nutrient at a time. Today’s re-
search in nutritional genomics involves all of the sciences, coor-
dinating their multiple findings, and explaining their
interactions among several genes, actions, and nutrients in rel-
atively little time. As a result, nutrition knowledge is growing at
an incredibly fast pace.
The recent surge in genomics research grew from the Human
Genome Project, an international effort by industry and govern-
ment scientists to identify and describe all of the genes in the hu-
man genome—that is, all the genetic information contained
within a person’s cells. Completed in 2003, this project developed
many of the research technologies needed to study genes and ge-
netic variation. Scientists are now working to identify the individual
proteins made by the genes, the genes associated with diseases,
and the dietary and lifestyle choices that most influence the expres-
sion of those genes. Such information will have major implications
for society in general, and for health care in particular.2
©
Science
VU/Visuals
Unlimited
Nutritional Genomics
chromosomes: structures within
the nucleus of a cell made of
DNA and associated proteins.
Human beings have 46
chromosomes in 23 pairs.
Each chromosome has many
genes.
DNA (deoxyribonucleic acid):
the double helix molecules of
which genes are made.
epigenetics: the study of
heritable changes in gene
function that occur without a
change in the DNA sequence.
gene expression: the process by
which a cell converts the
genetic code into RNA and
protein.
genes: sections of chromosomes
that contain the instructions
needed to make one or more
proteins.
genetics: the study of genes and
inheritance.
genomics: the study of all the
genes in an organism and their
interactions with environmental
factors.
human genome (GEE-nome): the
full complement of genetic
material in the chromosomes of
a person’s cells.
microarray technology: research
tools that analyze the expression
of thousands of genes
simultaneously and search for
particular gene changes
associated with a disease. DNA
microarrays are also called DNA
chips.
mutations: a permanent change
in the DNA that can be
inherited.
nucleotide bases: the nitrogen-
containing building blocks of
DNA and RNA—cytosine (C),
thymine (T), uracil (U), guanine
(G), and adenine (A). In DNA,
the base pairs are A–T and C–G
and in RNA, the base pairs are
A–U and C–G.
nucleotides: the subunits of DNA
and RNA molecules, composed
of a phosphate group, a 5-
carbon sugar (deoxyribose for
DNA and ribose for RNA), and a
nitrogen-containing base.
nutritional genomics: the
science of how food (and its
components) interacts with the
genome. The study of how
nutrients affect the activities of
genes is called nutrigenomics.
The study of how genes affect
the activities of nutrients is
called nutrigenetics.
phenylketonuria (FEN-il-KEY-toe-
NEW-ree-ah) or PKU: an
inherited disorder characterized
by failure to metabolize the
amino acid phenylalanine to
tyrosine.
RNA (ribonucleic acid): a
compound similar to DNA,
but RNA is a single strand with
a ribose sugar instead of a
deoxyribose sugar and uracil
instead of thymine as one of
its bases.
GLOSSARY

208 • Highlight 6
A Genomics Primer
Figure H6-1 shows the relationships among the materials that
comprise the genome. As Chapter 6’s discussion of protein syn-
thesis pointed out, genetic information is encoded in DNA mole-
cules within the nucleus of cells. The DNA molecules and
associated proteins are packed within 46 chromosomes. The
genes are segments of a DNA strand that can eventually be trans-
lated into one or more proteins. The sequence of nucleotide
bases within each gene determines the amino acid sequence of
a particular protein. Scientists currently estimate that there are
between 20,000 and 25,000 genes in the human genome.
As Figure 6-7 (p. 188) explained, when cells make proteins, a
DNA sequence is used to make messenger RNA. The nucleotide
sequence in messenger RNA then determines the amino acid se-
quence to make a protein. This process—from genetic information
to protein synthesis—is known as gene expression. Gene ex-
pression can be determined by measuring the amounts of messen-
ger RNA in a tissue sample. Microarray technology (see photo
on p. 207) allows researchers to detect messenger RNA and ana-
lyze the expression of thousands of genes simultaneously.
Simply having a certain gene does not determine that its associ-
ated trait will be expressed; the gene has to be activated. (Similarly,
owning lamps does not ensure you will have light in your home un-
less you turn them on.) Nutrients are among many environmental
factors that play key roles in either activating or silencing genes.
Switching genes on and off does not change the DNA itself, but it
can have dramatic consequences for a person’s health.
The area of study that examines how environmental factors in-
fluence gene expression without changing the DNA is known as
epigenetics. To turn genes on, enzymes attach proteins near the
beginning of a gene. If enzymes attach a methyl group (CH3) in-
stead, the protein is blocked from binding to the gene and the
gene remains switched off. Other factors influence gene expres-
sion as well, but methyl groups are currently the most well under-
stood. They also are known to have dietary connections.
The accompanying photo of two mice illustrates epigenetics and
how diet can influence genetic traits such as hair color and body
weight. Both mice have a gene that tends to produce fat, yellow
pups, but their mothers were given different diets. The mother of the
mouse on the right was given a dietary supplement containing the B
vitamins folate and vitamin B12. These nutrients silenced the gene for
“yellow and fat,” resulting in brown pups with normal appetites. As
Chapter 10 explains, one of the main roles of these B vitamins is to
transfer methyl groups. In the case of the supplemented mice,
methyl groups migrated onto DNA and shut off several genes, thus
producing brown coats and protecting against the development of
A chromosome is made of DNA
and associated proteins.
The human genome is a complete
set of genetic material organized
into 46 chromosomes, located
within the nucleus of a cell.
The double helical structure of a
DNA molecule is made up of two
long chains of nucleotides. Each
nucleotide is composed of a
phosphate group, a 5-carbon
sugar, and a base.
The sequence of nucleotide
bases (C, G, A, T) determines
the amino acid sequence of
proteins. These bases are
connected by hydrogen bonding
to form base pairs—adenine (A)
with thymine (T) and guanine (G)
with cytosine (C).
A gene is a segment of DNA that
includes the information needed to
synthesize one or more proteins.
1
1
2
3
4
5
2
3
4
5
Nucleus
Chromosome
DNA
Cell
Gene
C
C
C
C
G
G
G
G
T
T
T
T
T
T
A
A
A
A
A
A
A
FIGURE H6-1 The Human Genome
Adapted from “A Primer: From DNA to Life,” Human Genome Project, U.S. Department of Energy Office of Science; www.ornl.gov/sci/techresources/Human_Genome/

NUTRITIONAL GENOMICS • 209
obesity and some related diseases. Keep in mind that these changes
occurred epigenetically. In other words, the DNA sequence within
the genes of the mice remained the same.
Whether silencing or activating a gene is beneficial or harmful
depends on what the gene does. Silencing a gene that stimulates
cancer growth, for example, would be beneficial, but silencing a
gene that suppresses cancer growth would be harmful. Similarly,
activating a gene that defends against obesity would be beneficial,
but activating a gene that promotes obesity would be harmful.
Much research is under way to determine which nutrients activate
or silence which genes.
Genetic Variation
and Disease
Except for identical twins, no two persons are genetically identi-
cal. The variation in the genomes of any two persons, however, is
only about 0.1 percent, a difference of only one nucleotide base
in every 1000. Yet it is this incredibly small difference that makes
each of us unique and explains why, given the same environmen-
tal influences, some of us develop certain diseases and others do
not. Similarly, genetic variation explains why some of us respond
to interventions such as diet and others do not. For example, fol-
lowing a diet low in saturated fats will significantly lower LDL cho-
lesterol for most people, but the degree of change varies
dramatically among individuals, with some people having only a
small decrease or even a slight increase.3 In other words, dietary
factors may be more helpful or more harmful depending on a
person’s particular genetic variations.4 (Such findings help to ex-
plain some of the conflicting results from research studies.) The
goal of nutritional genomics is to custom design specific recom-
mendations that fit the needs of each individual. Such personal-
ized recommendations are expected to provide more effective
disease prevention and treatment solutions.
Diseases characterized by a single-gene disorder are geneti-
cally predetermined, usually exert their effects early in life, and
greatly affect those touched by them, but are relatively rare. The
cause and effect of single-gene disorders is clear—those with the
genetic defect get the disease and those without it don’t. In con-
trast, the more common diseases, such as heart disease and can-
cer, are influenced by many genes and typically develop over
several decades. These chronic diseases have multiple genetic
components that predispose the prevention or development of a
disease, depending on a variety of environmental factors (such as
smoking, diet, and physical activity).5 Both types are of interest to
researchers in nutritional genomics.
Single-Gene Disorders
Some disorders are caused by mutations in single genes that are
inherited at birth. The consequences of a missing or malfunction-
ing protein can seriously disrupt metabolism and may require sig-
nificant dietary or medical intervention. A classic example of a
diet-related, single-gene disorder is phenylketonuria, or PKU.
Approximately one in every 15,000 infants in the United States
is born with PKU. PKU arises from mutations in the gene that
codes for the enzyme that converts the essential amino acid
phenylalanine to the amino acid tyrosine. Without this enzyme,
phenylalanine and its metabolites accumulate and damage the
nervous system, resulting in mental retardation, seizures, and be-
havior abnormalities. At the same time, the body cannot make ty-
rosine or compounds made from it (such as the neurotransmitter
epinephrine). Consequently, tyrosine becomes an essential amino
acid: because the body cannot make it, the diet must supply it.
Although the most debilitating effect is on brain development,
other symptoms of PKU become evident if the condition is left un-
treated. Infants with PKU may have poor appetites and grow
slowly. They may be irritable or have tremors or seizures. Their
bodies and urine may have a musty odor. Their skin coloring may
be unusually pale, and they may develop skin rashes.
The effect of nutrition intervention in PKU is remarkable. In fact,
the only current treatment for PKU is a diet that restricts phenylala-
nine and supplies tyrosine to maintain blood levels of these amino
acids within safe ranges. Because all foods containing protein pro-
vide phenylalanine, the diet must depend on a formula to supply a
phenylalanine-free source of energy, protein, vitamins, and miner-
als. If the restricted diet is conscientiously followed, the symptoms
can be prevented. Because phenylalanine is an essential amino
acid, the diet cannot exclude it completely. Children with PKU need
phenylalanine to grow, but they cannot handle excesses without
detrimental effects. Therefore, their diets must provide enough
phenylalanine to support normal growth and health but not
enough to cause harm. The diet must also provide tyrosine. To en-
sure that blood concentrations of phenylalanine and tyrosine are
close to normal, children and adults who have PKU must have
blood tests periodically and adjust their diets as necessary.
Multigene Disorders
In multigene disorders, each of the genes can influence the pro-
gression of a disease, but no single gene causes the disease on its
Both of these mice have the gene that tends to produce fat, yellow
pups, but their mothers had different diets. The mother of the
mouse on the right received a dietary supplement, which silenced
the gene, resulting in brown pups with normal appetites.
©
Jirtle
and
Waterland

own. For this reason, genomics researchers must study the ex-
pression and interactions of multiple genes. Because multigene
disorders are often sensitive to interactions with environmental
influences, they are not as straightforward as single-gene disor-
ders. Heart disease provides an example of a chronic disease with
multiple gene and environmental influences. Consider that major
risk factors for heart disease include elevated blood cholesterol
levels, obesity, diabetes, and hypertension, yet the underlying ge-
netic and environmental causes of any of these individual risk fac-
tors is not completely understood. Genomic research can reveal
details about each of these risk factors. For example, tests could
determine whether blood cholesterol levels are high due to in-
creased cholesterol absorption or production or because of de-
creased cholesterol degradation.6 This information could then
guide physicians and dietitians to prescribe the most appropriate
medical and dietary interventions from among many possible so-
lutions.7 Today’s dietary recommendations advise a low-fat diet,
which helps people with a small type of LDL but not those with
the large type. In fact, a low-fat diet is actually more harmful for
people with the large type. Finding the best option for each per-
son will be a challenge given the many possible interactions be-
tween genes and environmental factors and the millions of
possible gene variations in the human genome that make each in-
dividual unique.8
The results of genomic research are helping to explain find-
ings from previous nutrition research. Consider dietary fat and
heart disease, for example. As Highlight 5 explained, epidemio-
logical and clinical studies have found that a diet high in unsatu-
rated fatty acids often helps to maintain a healthy blood lipid
profile. Now genetic studies offer an underlying explanation of
this relationship: diets rich in polyunsaturated fatty acids activate
genes responsible for making enzymes that break down fats and
silence genes responsible for making enzymes that make fats.9
Both actions change fat metabolism in the direction of lowering
blood lipids.
To learn more about how individuals respond to diet, re-
searchers examine the genetic differences between people. The
most common genetic differences involve a change in a single
nucleotide base located in a particular region of a DNA
strand—thymine replacing cytosine, for example. Such varia-
tions are called single nucleotide polymorphisms (SNPs), and
they commonly occur throughout the genome. Many SNPs
(commonly pronounced “snips”) have no effect on cell activity.
In fact, SNPs are significant only if they affect the amino acid
sequence of a protein in a way that alters its function and if that
function is critical to the body’s well-being. Research on a gene
that plays a key role in lipid metabolism reveals differences in a
person’s response to diet depending on whether the gene has
a common SNP. People with the SNP have lower LDL when eat-
ing a diet rich in polyunsaturated fatty acids—and higher LDL
with a low intake—than those without the SNP.10 These find-
ings clearly show how diet (in this case, polyunsaturated fat)
interacts with a gene (in this case, a fat metabolism gene with
a SNP) to influence the development of a disease (changing
blood lipids implicated in heart disease). The quest now is to
identify the genetic characteristics that predict various re-
sponses to dietary recommendations.11
Clinical Concerns
Because multigene, chronic diseases are common, an under-
standing of the human genome will have widespread ramifica-
tions for health care. This new understanding of the human
genome is expected to change health care by:
• Providing knowledge of an individual’s genetic predisposition to
specific diseases.
• Allowing physicians to develop “designer” therapies—prescribing
the most effective schedule of screening, behavior changes (in-
cluding diet), and medical interventions based on each individual’s
genetic profile.
• Enabling manufacturers to create new medications for each ge-
netic variation so that physicians can prescribe the best medicine in
the exact dose and frequency to enhance effectiveness and mini-
mize the risks of side effects.
• Providing a better understanding of the nongenetic factors that in-
fluence disease development.
Enthusiasm surrounding genomic research needs to be put
into perspective, however, in terms of the present status of clini-
cal medicine as well as people’s willingness to make difficult
lifestyle choices. Critics have questioned whether genetic markers
for disease would be more useful than simple clinical measure-
ments, which reflect both genetic and environmental influences.
In other words, knowing that a person is genetically predisposed
to have high blood cholesterol is not necessarily more useful than
knowing the person’s actual blood cholesterol level.12 Further-
more, if a disease has many genetic risk factors, each gene that
contributes to susceptibility may have little influence on its own,
so the benefits of identifying an individual genetic marker might
be small. The long-range possibility is that many genetic markers
will eventually be identified, and the hope is that the combined
information will be a useful and accurate predictor of disease.
Having the knowledge to prevent disease and actually taking
action do not always coincide. Despite the abundance of current
dietary recommendations, people seem unwilling to make behav-
ior changes known to improve their health. For example, it has
been estimated that heart disease and type 2 diabetes are 90 per-
cent preventable when people adopt an appropriate diet, main-
tain a healthy body weight, and exercise regularly.13 Yet these two
diseases remain among the leading causes of death. Given the
difficulty that people have with current recommendations, it may
be unrealistic to expect that many of them will enthusiastically
adopt an even more detailed list of lifestyle modifications. Then
again, compliance may be better when it is supported by infor-
mation based on a person’s own genetic profile.
The debate over nature versus nurture—whether genes or the
environment are more influential—has quieted. The focus has
shifted. Scientists acknowledge the important roles of each and
understand the real answers lie within the myriad interactions.
Current research is sorting through how nutrients (and other di-
etary factors) and genes confer health benefits or risks. Answers
from genomic research may not become apparent for years to
come, but the opportunities and rewards may prove well worth
the efforts.14
210 • Highlight 6

NUTRITIONAL GENOMICS • 211
1.G. T. Keusch, What do –omics mean for the
science and policy of the nutritional sci-
ences? American Journal of Clinical Nutrition
83 (2006): 520S–522S.
2. N. Fogg-Johnson and J. Kaput, Nutrige-
nomics: An emerging scientific discipline,
Food Technology 57 (2003): 60–67; R. Wein-
shilboum, Inheritance and drug response,
New England Journal of Medicine 348 (2003):
529–537; A. E. Guttmacher and F. S. Collins,
Genomic medicine—A primer, New England
Journal of Medicine 347 (2002): 1512–1520.
3. D. Corella and J. M. Ordovas, Single nucleo-
tide polymorphisms that influence lipid
metabolism: Interaction with dietary fac-
tors, Annual Review of Nutrition 25 (2005):
341–390.
4. E. Trujillo, C. Davis, and J. Milner, Nutrige-
nomics, proteomics, metabolomics, and the
practice of dietetics, Journal of the American
5. J. Kaput and coauthors, The case for strate-
gic international alliances to harness nutri-
tional genomics for public and personal
health, British Journal of Nutrition 94 (2005):
623–632; J. Kaput and R. L. Rodriguez,
Nutritional genomics: The next frontier in
the postgenome era, Physiological Genomics
16 (2004): 166–177.
6. J. B. German, M. A. Roberts, and S. M.
Watkins, Personal metabolomics as a next
generation nutritional assessment, Journal of
Nutrition 133 (2003): 4260–4266.
7. R. M. DeBusk and coauthors, Nutritional
genomics in practice: Where do we begin?
105 (2005): 589–597.
8. J. M. Ordovas, Nutrigenetics, plasma lipids,
and cardiovascular risk, Journal of the Ameri-
can Dietetic Association 106 (2006):
1074–1081.
9. H. Sampath and J. M. Ntambi, Polyunsatu-
rated fatty acid regulation of genes of lipid
metabolism, Annual Review of Nutrition 25
(2005): 317–340.
10. E. S. Tai and coauthors, Polyunsaturated
fatty acids interact with PPARA–L162V
polymorphism to affect plasma triglyceride
apolipoprotein C-III concentrations in the
Framingham Heart Study, Journal of Nutrition
135 (2005): 397–403.
11. J. M. Ordovas, The quest for cardiovascular
health in the genomic era: Nutrigenetics
and plasma lipoproteins, Proceedings of the
Nutrition Society 63 (2004): 145–152.
12. W. C. Willett, Balancing life-style and ge-
nomics research for disease prevention,
Science 296 (2002): 695–698.
13. S. Yusut and coauthors, Effect of potentially
modifiable risk factors associated with
myocardial infarction in 52 countries (the
INTERHEART Study): Case-control study,
Lancet 364 (2004): 937–952; Willett, 2002.
14. A. E. Guttmacher and F. S. Collins, Realizing
the promise of genomics in biomedical
research, Journal of the American Medical
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REFERENCES
• Get information about human genomic discoveries and
how they can be used to improve health from the Ge-
nomics and Disease Prevention site of the Centers for
Disease Control: www.cdc.gov/genomics

You eat breakfast and hustle off to class. After lunch, you study for tomorrow’s
exam. Dinner is followed by an evening of dancing. Do you ever think about
how the food you eat powers the activities of your life? What happens when
you don’t eat—or when you eat too much? Learn how the cells of your body
transform carbohydrates, fats, and proteins into energy—and what happens
when you give your cells too much or too little of any of these nutrients.
Discover the metabolic pathways that lead to body fat and those that support
physical activity. It’s really quite fascinating.
The CengageNOW logo
Figure 7.5: Animated! Glycolysis: Glucose-to-Pyruvate
Figure 7.10: Animated! Fatty Acid-to-Acetyl CoA
Figure 7.18: Animated! The TCA Cycle
Figure 7.19: Animated! Electron Transport Chain
and ATP Synthesis
© Burke/Triolo Productions/FoodPix/Jupiter Images

Energy makes it possible for people to breathe, ride bicycles, compose mu-
sic, and do everything else they do. All the energy that sustains human life
initially comes from the sun—the ultimate source of energy. As Chapter 1
explained, energy is the capacity to do work. Although every aspect of our
lives depends on energy, the concept of energy can be difficult to grasp be-
cause it cannot be seen or touched, and it manifests in various forms, in-
cluding heat, mechanical, electrical, and chemical energy. In the body,
heat energy maintains a constant body temperature, and electrical energy
sends nerve impulses. Energy is stored in foods and in the body as chemi-
cal energy.
During photosynthesis, plants make simple sugars from carbon diox-
ide and capture the sun’s light energy in the chemical bonds of those sug-
ars. Then human beings eat either the plants or animals that have eaten
the plants. These foods provide energy, but how does the body obtain that
energy from foods? This chapter answers that question by following the
nutrients that provide the body with fuel through a series of reactions that
release energy from their chemical bonds. As the bonds break, they release
energy in a controlled version of the same process by which wood burns in
a fire. Both wood and food have the potential to provide energy. When
wood burns in the presence of oxygen, it generates heat and light (energy),
steam (water), and some carbon dioxide and ash (waste). Similarly, during
metabolism, the body releases energy, water, and carbon dioxide.
By studying metabolism, you will understand how the body uses foods
to meet its needs and why some foods meet those needs better than others.
Readers who are interested in weight control will discover which foods con-
tribute most to body fat and which to select when trying to gain or lose
weight safely. Physically active readers will discover which foods best sup-
port endurance activities and which to select when trying to build lean
body mass.
213
CHAPTER OUTLINE
Chemical Reactions in the Body
Breaking Down Nutrients for Energy
• Glucose • Glycerol and Fatty Acids •
Amino Acids • Breaking Down Nutrients
for Energy—In Summary • The Final
Steps of Catabolism
Energy Balance • Feasting—Excess
Energy • The Transition from Feasting to
Fasting • Fasting—Inadequate Energy
HIGHLIGHT 7 Alcohol and Nutrition
7
Metabolism:
Transformations
and Interactions
C H A P T E R
photosynthesis: the process by which
green plants use the sun’s energy to make
carbohydrates from carbon dioxide and
water.
• photo = light
• synthesis = put together (making)
fuel: compounds that cells can use for energy.
The major fuels include glucose, fatty acids,
and amino acids; other fuels include ketone
bodies, lactate, glycerol, and alcohol.
metabolism: the sum total of all the
chemical reactions that go on in living cells.
Energy metabolism includes all the reactions
by which the body obtains and expends the
energy from food.
• metaballein = change

214 • CHAPTER 7
Chemical Reactions in the Body
Earlier chapters introduced some of the body’s chemical reactions: the making and
breaking of the bonds in carbohydrates, lipids, and proteins. Metabolism is the sum
of these and all the other chemical reactions that go on in living cells; energy metab-
olism includes all the ways the body obtains and uses energy from food.
The Site of Metabolic Reactions—Cells The human body is made up of tril-
lions of cells, and each cell busily conducts its metabolic work all the time. (Appen-
dix A presents a brief summary of the structure and function of the cell.) Figure 7-1
depicts a typical cell and shows where the major reactions of energy metabolism
take place. The type and extent of metabolic activities vary depending on the type
of cell, but of all the body’s cells, the liver cells are the most versatile and metaboli-
cally active. Table 7-1 offers insights into the liver’s work.
The Building Reactions—Anabolism Earlier chapters described how condensa-
tion reactions combine the basic units of energy-yielding nutrients to build body
compounds. Glucose molecules may be joined together to make glycogen chains.
Glycerol and fatty acids may be assembled into triglycerides. Amino acids may be
linked together to make proteins. Each of these reactions starts with small, simple
compounds and uses them as building blocks to form larger, more complex struc-
tures. Because such reactions involve doing work, they require energy. The building
up of body compounds is known as anabolism. Anabolic reactions are represented
in this book, wherever possible, with “up” arrows in chemical diagrams (such as
those shown in Figure 7-2).
A membrane encloses each cell’s
contents and regulates the passage
of molecules in and out of the cell.
Inside the cell membrane lies the
cytoplasm, a lattice-type structure
that supports and controls the
movement of the cell’s structures.
A protein-rich jelly-like fluid called
cytosol fills the spaces within the
lattice. The cytosol contains the
enzymes involved in glycolysis.a
A separate inner membrane
encloses the cell’s nucleus.
Outer membrane
(site of fatty
acid activation)
Outer compartment
Inner membrane
(site of electron
transport chain)
Inner compartment
(site of pyruvate-to-acetyl
CoA, fatty acid oxidation,
and TCA cycle)
A mitochondrion
Cytosol
(site of
glycolysis)
Inside the nucleus are the
chromosomes, which
contain the genetic
material DNA.
Known as the “powerhouses”
of the cells, the mitochondria
are intricately folded membranes
that house all the enzymes
involved in the conversion of
pyruvate to acetyl CoA, fatty
acid oxidation, the TCA cycle,
and the electron transport
chain.b
The ribosomes, some of which
are located on a system of
intracellular membranes,
assemble amino acids
into proteins.
c
FIGURE 7-1 A Typical Cell (Simplified Diagram)
aGlycolysis is introduced on p. 219.
bThe conversion of pyruvate to acetyl CoA, fatty acid oxidation, the TCA cycle, and the electron transport chain are described later in the chapter..
cFigure 6-7 on p. 188 describes protein synthesis.
anabolism (an-AB-o-lism): reactions in which
small molecules are put together to build
larger ones. Anabolic reactions require
energy.
• ana = up

METABOLISM: TRANSFORMATIONS AND INTERACTIONS • 215
TABLE 7-1 Metabolic Work of the Liver
The liver is the most active processing center in the body. When nutrients enter the body from the diges-
tive tract, the liver receives them first; then it metabolizes, packages, stores, or ships them out for use by
other organs. When alcohol, drugs, or poisons enter the body, they are also sent directly to the liver; here
they are detoxified and their by-products shipped out for excretion. An enthusiastic anatomy and physiol-
ogy professor once remarked that given the many vital activities of the liver, we should express our feel-
ings for others by saying, “I love you with all my liver,” instead of “with all my heart.” Granted, this decla-
ration lacks romance, but it makes a valid point. Here are just some of the many jobs performed by the
liver. To renew your appreciation for this remarkable organ, review Figure 3-12 on p. 85.
Carbohydrates:
• Converts fructose and galactose to glucose
• Makes and stores glycogen
• Breaks down glycogen and releases glucose
• Breaks down glucose for energy when needed
• Makes glucose from some amino acids and glycerol when needed
• Converts excess glucose to fatty acids
Lipids:
• Builds and breaks down triglycerides, phospholipids, and cholesterol as
needed
• Breaks down fatty acids for energy when needed
• Packages extra lipids in lipoproteins for transport to other body organs
• Manufactures bile to send to the gallbladder for use in fat digestion
• Makes ketone bodies when necessary
Proteins:
• Manufactures nonessential amino acids that are in short supply
• Removes from circulation amino acids that are present in excess of need and
converts them to other amino acids or deaminates them and converts them
to glucose or fatty acids
• Removes ammonia from the blood and converts it to urea to be sent to the
kidneys for excretion
• Makes other nitrogen-containing compounds the body needs (such as bases
used in DNA and RNA)
• Makes plasma proteins such as clotting factors
Other:
• Detoxifies alcohol, other drugs, and poisons; prepares waste products for
excretion
• Helps dismantle old red blood cells and captures the iron for recycling
• Stores most vitamins and many minerals
Uses
energy
Uses
energy
Uses
energy
Yields
energy
Yields
energy
Yields
energy
Yields
energy
ANABOLIC REACTIONS
Glycogen
Glucose
Protein
Amino acids
CATABOLIC REACTIONS
Protein
Amino acids Amino acids
+
Triglycerides
Glycerol Fatty acids
Anabolic reactions include the making of glycogen, triglycerides, and protein; these reactions require differing amounts of energy.
Catabolic reactions include the breakdown of glycogen, triglycerides, and protein; the further catabolism of glucose, glycerol, fatty
acids, and amino acids releases differing amounts of energy. Much of the energy released is captured in the bonds of adenosine
triphosphate (ATP).
NOTE: You need not memorize a color code to understand the figures in this chapter, but you may find it helpful to know that blue
is used for carbohydrates, yellow for fats, and red for proteins.
Triglycerides
Glycerol Fatty acids
+
Glycogen
Glucose Glucose
+
FIGURE 7-2 Anabolic and Catabolic Reactions Compared

216 • CHAPTER 7
The Breakdown Reactions—Catabolism The breaking down of body com-
pounds is known as catabolism; catabolic reactions release energy and are repre-
sented, wherever possible, by “down” arrows in chemical diagrams (as in Figure 7-2,
p. 215). Earlier chapters described how hydrolysis reactions break down glycogen to
glucose, triglycerides to fatty acids and glycerol, and proteins to amino acids. When
the body needs energy, it breaks down any or all of these four basic units into even
smaller units, as described later.
The Transfer of Energy in Reactions—ATP High-energy storage com-
pounds in the body capture some of the energy released during the breakdown
of glucose, glycerol, fatty acids, and amino acids from foods. One such com-
pound is ATP (adenosine triphosphate). ATP, as its name indicates, con-
tains three phosphate groups (see Figure 7-3). ◆ The bonds connecting the
phosphate groups are often described as “high-energy” bonds, referring to the
bonds’ readiness to release their energy. The negative charges on the phosphate
groups make ATP vulnerable to hydrolysis. Whenever cells do any work that
requires energy, hydrolytic reactions readily break these high-energy bonds
of ATP, splitting off one or two phosphate groups and releasing their
energy.
Quite often, the hydrolysis of ATP occurs simultaneously with reactions that
will use that energy—a metabolic duet known as coupled reactions. Figure 7-4
illustrates how the body captures and releases energy in the bonds of ATP. In
essence, the body uses ATP to transfer the energy released during catabolic reac-
tions to power its anabolic reactions. The body converts the chemical energy of
food to the chemical energy of ATP with about 50 percent efficiency, radiating the
rest as heat.1 Energy is lost as heat again when the body uses the chemical energy
of ATP to do its work—moving muscles, synthesizing compounds, or transporting
nutrients, for example.
The Helpers in Metabolic Reactions—Enzymes and Coenzymes Metabolic
reactions almost always require enzymes ◆ to facilitate their action. In many
cases, the enzymes need assistants to help them. Enzyme helpers are called
coenzymes. ◆
Coenzymes are complex organic molecules that associate closely with most en-
zymes but are not proteins themselves. The relationships between various coen-
zymes and their respective enzymes may differ in detail, but one thing is true of
all: without its coenzyme, an enzyme cannot function. Some of the B vitamins
serve as coenzymes that participate in the energy metabolism of glucose, glycerol,
fatty acids, and amino acids (Chapter 10 provides more details).
Adenosine + 3 phosphate groups
O
N
NH2
N N
N
OH OH
O
CH2 O
O-
O
O
O-
O
P P O
O-
O-
P
FIGURE 7-3 ATP (Adenosine Triphosphate)
ATP is one of the body’s high-energy molecules. Notice that the bonds connecting
the three phosphate groups have been drawn as wavy lines, indicating a high-
energy bond. When these bonds are broken, energy is released.
catabolism (ca-TAB-o-lism): reactions in
which large molecules are broken down to
smaller ones. Catabolic reactions release
energy.
• kata = down
ATP or adenosine (ah-DEN-oh-seen)
triphosphate (try-FOS-fate): a common
high-energy compound composed of a
purine (adenine), a sugar (ribose), and three
phosphate groups.
coupled reactions: pairs of chemical
reactions in which some of the energy
released from the breakdown of one
compound is used to create a bond in the
formation of another compound.
coenzymes: complex organic molecules that
work with enzymes to facilitate the enzymes’
activity. Many coenzymes have B vitamins as
part of their structures (Figure 10-1 on p.
327 in Chapter 10 illustrates coenzyme
action).
• co = with
◆ ATP = A-P~P~P.
(Each ~ denotes a “high-energy” bond.)
◆ Reminder: Enzymes are protein catalysts—
proteins that facilitate chemical reactions
without being changed in the process.
◆ The general term for substances that facili-
tate enzyme action is cofactors; they
include both organic coenzymes made from
vitamins and inorganic substances such as
minerals.

A P P P
A P P P
+
ADP + P
ATP
Energy from ATP is released
when a high-energy
phosphate bond is broken.
This energy is used in a
coupled reaction to do the
body’s work. With the loss
of a phosphate group, ATP
becomes ADP.
Energy from the breakdown of
carbohydrate, fat, and protein
is used to attach a phosphate
group to ADP, making ATP.
ATP captures and stores
energy in the bonds
between its phosphate
groups.
FIGURE 7-4 Transfer of Energy by ATP—A Coupled Reaction
The breakdown of ATP (adenosine triphosphate) to ADP (adenosine diphosphate)
releases energy that can be used to power another reaction (such as the synthesis
of a needed compound). The simultaneous occurrence of one reaction releasing
energy and another reaction using the energy is called a coupled reaction.
During digestion the energy-yielding nutrients—carbohydrates, lipids, and
proteins—are broken down to glucose (and other monosaccharides), glycerol,
fatty acids, and amino acids. Aided by enzymes and coenzymes, the cells use
these products of digestion to build more complex compounds (anabolism) or
break them down further to release energy (catabolism). High-energy com-
pounds such as ATP may capture the energy released during catabolism.
IN SUMMARY
Breaking Down Nutrients for Energy
Chapters 4, 5, and 6 laid the groundwork for the study of metabolism; a brief review
may be helpful. During digestion, the body breaks down the three energy-yielding
nutrients—carbohydrates, lipids, and proteins—into four basic units that can be ab-
sorbed into the blood:
• From carbohydrates—glucose (and other monosaccharides)
• From fats (triglycerides)—glycerol and fatty acids
• From proteins—amino acids
The body uses carbohydrates and fats for most of its energy needs. Amino acids are
used primarily as building blocks for proteins, but they also enter energy pathways,
contributing about 10 to 15 percent of the day’s energy use. Look for these four ba-
sic units—glucose, glycerol, fatty acids, and amino acids—to appear again and
again in the metabolic reactions described in this chapter. Alcohol also enters many
of the metabolic pathways; Highlight 7 focuses on how alcohol disrupts metabolism
and how the body handles it.
Glucose, glycerol, fatty acids, and amino acids are the basic units derived from
food, but a molecule of each of these compounds is made of still smaller units, the
atoms—carbons, nitrogens, oxygens, and hydrogens. During catabolism, the body

218 • CHAPTER 7
separates these atoms from one another. To follow this action, recall how many
carbons are in the “backbones” of these compounds:
• Glucose has 6 carbons:
• Glycerol has 3 carbons:
• A fatty acid usually has an even number of carbons, commonly 16 or 18
carbons:*
• An amino acid has 2, 3, or more carbons with a nitrogen attached:†
Full chemical structures and reactions appear both in the earlier chapters and in Ap-
pendix C; this chapter diagrams the reactions using just the compounds’ carbon
and nitrogen backbones.
As you will see, each of the compounds—glucose, glycerol, fatty acids, and
amino acids—starts down a different path. Along the way, two new names ap-
pear—pyruvate (a 3-carbon structure) and acetyl CoA (a 2-carbon structure with
a coenzyme, CoA, attached)—and the rest of the story falls into place around
them.‡ Two major points to notice in the following discussion:
• Pyruvate can be used to make glucose.
• Acetyl CoA cannot be used to make glucose.
A key to understanding these metabolic pathways is learning which fuels can
be converted to glucose and which cannot. The parts of protein and fat that can
be converted to pyruvate can provide glucose for the body, whereas the parts that
are converted to acetyl CoA cannot provide glucose but can readily provide fat.
The body must have glucose to fuel the activities of the central nervous system
and red blood cells. Without glucose from food, the body will devour its own lean
(protein-containing) tissue to provide the amino acids to make glucose. Therefore,
to keep this from happening, the body needs foods that can provide glucose—pri-
marily carbohydrate. Giving the body only fat, which delivers mostly acetyl CoA,
puts it in the position of having to break down protein tissue to make glucose. Giv-
ing the body only protein puts it in the position of having to convert protein to
glucose. Clearly, the best diet ◆ provides ample carbohydrate, adequate protein,
and some fat.
Eventually, all of the energy-yielding nutrients can enter the common path-
ways of the TCA cycle and the electron transport chain. (Similarly, people
from three different cities can all enter an interstate highway and travel to the
same destination.) The TCA cycle and electron transport chain have central roles
in energy metabolism and receive full attention later in the chapter. First, the text
describes how each of the energy-yielding nutrients is broken down to acetyl CoA
and other compounds in preparation for their entrance into these final energy
pathways.
* The figures in this chapter show 16- or 18-carbon fatty acids. Fatty acids may have 4 to 20 or more
carbons, with chain lengths of 16 and 18 carbons most prevalent.
† The figures in this chapter usually show amino acids as compounds of 2, 3, or 5 carbons arranged in a
straight line, but in reality amino acids may contain other numbers of carbons and assume other struc-
tural shapes (see Appendix C).
‡ The term pyruvate means a salt of pyruvic acid. (Throughout this book, the ending –ate is used inter-
changeably with –ic acid; for our purposes they mean the same thing.)
All the energy used to keep the heart beating,
the brain thinking, and the legs running
comes from the carbohydrates, fats, and
proteins in foods.
◆ A healthy diet provides:
• 45–65% kcalories from carbohydrate
• 10–35% kcalories from protein
• 20–35% kcalories from fat
C C C C C C
C C C
C C C C C C C C
C
C
C
C
C
C
C
C
C C C
C C C C C
C C
N
N N
pyruvate (PIE-roo-vate): a 3-carbon
compound that plays a key role in energy
metabolism.
acetyl CoA (ASS-eh-teel, or ah-SEET-il, coh-
AY): a 2-carbon compound (acetate, or
acetic acid, shown in Figure 5-1 on p. 140)
to which a molecule of CoA is attached.
CoA (coh-AY): coenzyme A; the coenzyme
derived from the B vitamin pantothenic acid
and central to energy metabolism.
TCA cycle or tricarboxylic (try-car-box-ILL-
ick) acid cycle: a series of metabolic
reactions that break down molecules of
acetyl CoA to carbon dioxide and hydrogen
atoms; also called the Kreb’s cycle after the
biochemist who elucidated its reactions.
electron transport chain: the final pathway
in energy metabolism that transports
electrons from hydrogen to oxygen and
captures the energy released in the bonds
of ATP.
COOH
C O
CH3
©
Chris
Cole/The
Image
Bank/Getty
Images

Glucose
What happens to glucose, glycerol, fatty acids, and amino acids during energy me-
tabolism can best be understood by starting with glucose. This discussion features
glucose because of its central role in carbohydrate metabolism and because liver cells
can convert the other monosaccharides (fructose and galactose) to compounds that
enter the same energy pathways.
Glucose-to-Pyruvate The first pathway glucose takes on its way to yield energy
is called glycolysis (glucose splitting).* Figure 7-5 shows a simplified drawing of
glycolysis. (This pathway actually involves several steps and several enzymes, which
Glucose
A little ATP is used to start glycolysis.
Galactose and fructose enter glycolysis
at different places, but all continue on
the same pathway.
These 3-carbon compounds are
converted to pyruvate. Glycolysis of
one molecule of glucose produces
two molecules of pyruvate.
A little ATP is produced, and coenzymes
carry the hydrogens and their electrons
to the electron transport chain.
NOTE: These arrows point down indicating
the breakdown of glucose to pyruvate during
energy metabolism. (Alternatively, the arrows
could point up indicating the making of glucose
from pyruvate, but that is not the focus of this
discussion.)
In a series of reactions, the 6-carbon
glucose is converted to other 6-carbon
compounds, which eventually split
into two interchangeable 3-carbon
compounds.
Uses energy
(ATP)
Uses energy
(ATP)
2 Pyruvate
Yields energy
(ATP)
Yields energy
(ATP)
C C C
C
C C
C C C
C
C C
C
C C C
C C
C
C C
C
C C
C
C C
C
C C
C C C
C
C C
C C C
C
C C
C
C C
C
C C
C
C C
C
C C
C
C C
C
C C
Coenzyme
Coenzyme
Coenzyme
e–
H+
Coenzyme
e–
H+
To Electron
Transport
Chain
FIGURE 7-5 Animated! Glycolysis: Glucose-to-Pyruvate
This simplified overview of glycolysis illustrates the steps in the process of converting
glucose to pyruvate. Appendix C provides more details.
* Glycolysis takes place in the cytosol of the cell (see Figure 7-1, p. 214).
glycolysis (gly-COLL-ih-sis): the metabolic
breakdown of glucose to pyruvate. Glycolysis
does not require oxygen (anaerobic).
• glyco = glucose
• lysis = breakdown
To test your understanding of these
concepts, log on to academic.cengage
.com/login.

220 • CHAPTER 7
are shown in Appendix C.) In a series of reactions, the 6-carbon glucose is converted
to similar 6-carbon compounds before being split in half, forming two 3-carbon
compounds. These 3-carbon compounds continue along the pathway until they are
converted to pyruvate. Thus the net yield of one glucose molecule is two pyruvate
molecules. The net yield of energy at this point is small; to start glycolysis, the cell
uses a little energy and then produces only a little more than it had to invest ini-
tially.* In addition, as glucose breaks down to pyruvate, hydrogen atoms with their
electrons are released and carried to the electron transport chain by coenzymes
made from the B vitamin niacin. A later section of the chapter explains how oxygen
accepts the electrons and combines with the hydrogens to form water and how the
process captures energy in the bonds of ATP.
This discussion focuses primarily on the breakdown of glucose for energy, but if
needed, cells in the liver (and to some extent, the kidneys) can make glucose again
from pyruvate in a process similar to the reversal of glycolysis. Making glucose requires
energy, however, and a few different enzymes. Still, glucose can be made from pyru-
vate, so the arrows between glucose and pyruvate could point up as well as down. ◆
Pyruvate’s Options Pyruvate may enter either an anaerobic or an aerobic en-
ergy pathway. When the body needs energy quickly—as occurs when you run a
quarter mile as fast as you can—pyruvate is converted to lactate in an anaerobic
pathway. When energy expenditure proceeds at a slower pace—as occurs when you
ride a bike for an hour—pyruvate breaks down to acetyl CoA in an aerobic pathway.
The following paragraphs explain these pathways.
Pyruvate-to-Lactate As mentioned earlier, coenzymes carry the hydrogens from glu-
cose breakdown to the electron transport chain. If the electron transport chain is un-
able to accept these hydrogens, as may occur when cells lack sufficient mitochondria
(review Figure 7-1, p. 214) or in the absence of sufficient oxygen, pyruvate can accept
the hydrogens. As Figure 7-6 shows, by accepting the hydrogens, pyruvate becomes
◆ Glucose may go “down” to make pyruvate,
or pyruvate may go “up” to make glucose,
depending on the cell’s needs.
Pyruvate
Glucose
C C C
C
C C C C C
C
C C
C
C C
C
C C
C
C C
C
C C
C
C C
C
C C
Yields energy
(ATP)
Uses energy
(ATP)
Coenzyme
Coenzyme
Coenzyme
OH
OH
O
O
Coenzyme
Coenzyme
Coenzyme
H
H
In the muscle:
Glucose
Glucose returns to
the muscles
Lactate travels
to the liver
Glucose
2 Lactate 2 Lactate
2 Pyruvate
Working muscles break down most of their glucose molecules
anaerobically to pyruvate. If the cells lack sufficient mitochondria or in
the absence of sufficient oxygen, pyruvate can accept the hydrogens
from glucose breakdown and become lactate. This conversion frees
the coenzymes so that glycolysis can continue.
Liver enzymes can convert
lactate to glucose, but this
reaction requires energy. The
process of converting lactate
from the muscles to glucose in
the liver that can be returned to
the muscles is known as the
Cori cycle.
In the liver:
OH
OH
FIGURE 7-6 Pyruvate-to-Lactate
* The cell uses 2 ATP to begin the breakdown of glucose to pyruvate, but it then gains 4 ATP for a net
gain of 2 ATP.
anaerobic (AN-air-ROE-bic): not requiring
oxygen.
• an = not
aerobic (air-ROE-bic): requiring oxygen.
mitochondria (my-toh-KON-dree-uh): the
cellular organelles responsible for producing
ATP; made of membranes (lipid and protein)
with enzymes mounted on them.
• mitos = thread (referring to their slender
shape)
• chondros = cartilage (referring to their
external appearance)

lactate, and the coenzymes are freed to return to glycolysis to pick up more hydrogens.
In this way, glucose can continue providing energy anaerobically for a while (see the
left side of Figure 7-6).
The production of lactate occurs to a limited extent even at rest. During high-
intensity exercise, however, the muscles rely heavily on anaerobic glycolysis to pro-
duce ATP quickly and the concentration of lactate increases dramatically. The
rapid rate of glycolysis produces abundant pyruvate and releases hydrogen-
carrying coenzymes more rapidly than the mitochondria can handle them. To en-
able exercise to continue at this intensity, pyruvate is converted to lactate and coen-
zymes are released, which allows glycolysis to continue (as mentioned earlier). The
accumulation of lactate in the muscles coincides with—but is not the cause of—the
subsequent drop in blood pH, burning pain, and fatigue that are commonly associ-
ated with intense exercise.2 In fact, making lactate from pyruvate consumes two hy-
drogen ions, which actually diminishes acidity and improves the performance of
tired muscles.3 A person performing the same exercise following endurance train-
ing actually experiences less discomfort—in part because the number of mitochon-
dria in the muscle cells have increased. This adaptation improves the mitochondria’s
ability to keep pace with the muscles’ demand for energy.
One possible fate of lactate is to be transported from the muscles to the liver.
There the liver can convert the lactate produced in muscles to glucose, which can
then be returned to the muscles. This recycling process is called the Cori cycle (see
Figure 7-6). (Muscle cells cannot recycle lactate to glucose because they lack a nec-
essary enzyme.)
Whenever carbohydrates, fats, or proteins are broken down to provide energy,
oxygen is always ultimately involved in the process. The role of oxygen in metabo-
lism is worth noticing, for it helps our understanding of physiology and metabolic re-
actions. The breakdown of glucose-to-pyruvate-to-lactate proceeds without oxygen—
it is anaerobic. This anaerobic pathway yields energy quickly, but it cannot be
sustained for long—a couple of minutes at most. Conversely, the aerobic pathways
produce energy more slowly, but because they can be sustained for a long time, their
total energy yield is greater.
Pyruvate-to-Acetyl CoA If the cell needs energy and oxygen is available, pyruvate
molecules enter the mitochondria of the cell (review Figure 7-1, p. 214). There a carbon
group (COOH) from the 3-carbon pyruvate is removed to produce a 2-carbon com-
pound that bonds with a molecule of CoA, becoming acetyl CoA. The carbon group
from pyruvate becomes carbon dioxide, which is released into the blood, circulated to
the lungs, and breathed out. Figure 7-7 diagrams the pyruvate-to-acetyl CoA reaction.
The step from pyruvate to acetyl CoA is metabolically irreversible: a cell cannot
retrieve the shed carbons from carbon dioxide to remake pyruvate and then glucose.
It is a one-way step and is therefore shown with only a “down” arrow in Figure 7-8.
C
C
C
C C
C
C C
C C
C C
Each pyruvate loses a carbon as carbon dioxide
and picks up a molecule of CoA, becoming acetyl
CoA. The arrow goes only one way (down)
because the step is not reversible. Result: 1
glucose yields 2 pyruvate, which yield 2 carbon
dioxide and 2 acetyl CoA.
2 Carbon
dioxide
2 CoA
2 Pyruvate
To TCA Cycle
Coenzyme
e–
H+
Coenzyme
Coenzyme
e–
H+
To Electron
Transport
Chain
Coenzyme
2 Acetyl CoA
CoA
CoA
FIGURE 7-7 Pyruvate-to-Acetyl CoA
Glucose
Acetyl CoA Fatty acids
Amino acids
(ketogenic)
Amino acids
(glucogenic)
Glycerol
Lactate
Pyruvate
NOTE: Amino acids that can be used to make glucose are called glucogenic; amino acids that
are converted to acetyl CoA are called ketogenic.
FIGURE 7-8 The Paths of Pyruvate and Acetyl CoA
Pyruvate may follow several reversible paths, but the path from pyruvate to acetyl
CoA is irreversible.
lactate: a 3-carbon compound produced
from pyruvate during anaerobic metabolism.
Cori cycle: the path from muscle glycogen to
glucose to pyruvate to lactate (which travels
to the liver) to glucose (which can travel
back to the muscle) to glycogen; named
after the scientist who elucidated this
pathway.
©
Jim
Cummins/Taxi/Getty
Images
The anaerobic breakdown of glucose-to-pyru-
vate-to-lactate is the major source of energy for
short, intense exercise.
COOH
C OH
CH3

222 • CHAPTER 7
Acetyl CoA’s Options Acetyl CoA has two main functions—it may be used to
synthesize fats or to generate ATP. When ATP is abundant, acetyl CoA makes fat, the
most efficient way to store energy for later use when energy may be needed. Thus
any molecule that can make acetyl CoA—including glucose, glycerol, fatty acids,
and amino acids—can make fat. In reviewing Figure 7-8, notice that acetyl CoA can
be used as a building block for fatty acids, but it cannot be used to make glucose or
amino acids.
When ATP is low and the cell needs energy, acetyl CoA may proceed through the
TCA cycle, releasing hydrogens, with their electrons, to the electron transport
chain. The story of acetyl CoA continues on p. 227 after a discussion of how fat and
protein arrive at the same crossroads. For now, know that when acetyl CoA from
the breakdown of glucose enters the aerobic pathways of the TCA cycle and elec-
tron transport chain, much more ATP is produced than during glycolysis. The role
of glycolysis is to provide energy for short bursts of activity and to prepare glucose
for later energy pathways.
C C
C
C
C C
2 Pyruvate
C
C C
C
C C
Glucose
Uses energy
(ATP)
Uses energy
(ATP)
Yields energy
(ATP)
Yields energy
(ATP)
C C C
C
C C
C C C
C
C C
C
C C C
C C
C
C C
C
C C
C
C C
C
C C
C C C
C
C C
C C C
C
C C
C
C C
C
C C
C
C C
C
C C
Coenzyme
Coenzyme
Coenzyme
e–
H+
Coenzyme
e–
H+
To Electron
Transport
Chain
Coenzyme
Coenzyme
Coenzyme
e–
H+
2 CoA
2 Acetyl CoA
CoA
CoA
To TCA Cycle
2 Carbon
dioxide
Coenzyme
e–
H+
To Electron
Transport
Chain
FIGURE 7-9 Glucose Enters the Energy
Pathway
This figure combines Figure 7-5 and
Figure 7-7 to show the breakdown of
glucose-to-pyruvate-to-acetyl CoA.
Details of the TCA cycle and the elec-
tron transport chain are given later
and in Appendix C.
The breakdown of glucose to energy begins with glycolysis, a pathway that
produces pyruvate. Keep in mind that glucose can be synthesized only from
pyruvate or compounds earlier in the pathway. Pyruvate may be converted to
lactate anaerobically or to acetyl CoA aerobically. Once the commitment to
acetyl CoA is made, glucose is not retrievable; acetyl CoA cannot go back to
glucose. Figure 7-9 summarizes the breakdown of glucose.
IN SUMMARY
Glycerol and Fatty Acids
Once glucose breakdown is understood, fat and protein breakdown are easily
learned, for all three eventually enter the same metabolic pathways. Recall that
triglycerides can break down to glycerol and fatty acids.
Glycerol-to-Pyruvate Glycerol is a 3-carbon compound like pyruvate but with a
different arrangement of H and OH on the C. As such, glycerol can easily be con-
verted to another 3-carbon compound that can go either “up” the pathway to
form glucose or “down” to form pyruvate and then acetyl CoA (review Figure 7-8,
p. 221).
Fatty Acids-to-Acetyl CoA Fatty acids are taken apart 2 carbons at a time in a
series of reactions known as fatty acid oxidation.* Figure 7-10 illustrates fatty
acid oxidation and shows that in the process, each 2-carbon fragment splits off
and combines with a molecule of CoA to make acetyl CoA. As each 2-carbon frag-
ment breaks off from a fatty acid during oxidation, hydrogens and their electrons
are released and carried to the electron transport chain by coenzymes made from
the B vitamins riboflavin and niacin. Figure 7-11 (p. 224) summarizes the break-
down of fats.
Fatty Acids Cannot Be Used to Synthesize Glucose When carbohydrate is
unavailable, the liver cells can make glucose from pyruvate and other 3-carbon
compounds, such as glycerol, but they cannot make glucose from the 2-carbon frag-
ments of fatty acids. In chemical diagrams, the arrow between pyruvate and acetyl
CoA always points only one way—down—and fatty acid fragments enter the meta-
bolic path below this arrow (review Figure 7-8, p. 221). The down arrow indicates
that fatty acids cannot be used to make glucose.
* Oxidation of fatty acids occurs in the mitochondria of the cells (see Figure 7-1, p. 214).
fatty acid oxidation: the metabolic
breakdown of fatty acids to acetyl CoA; also
called beta oxidation.

To TCA
Cycle
Coenzyme
Coenzyme
Coenzyme
Coenzyme
e–
H+
e–
H+
To Electron
Transport
Chain
Uses energy
(ATP)
H
H
H
O
OH
16-C fatty acid
Another CoA joins the chain, and the
bond at the second carbon (the beta-
carbon) weakens. Acetyl CoA splits off,
leaving a fatty acid that is two carbons
shorter.
Net result from a 16-C fatty acid: 14-C fatty acid CoA 1 acetyl CoA
+
12-C fatty acid CoA 2 acetyl CoA
+
Cycle repeats, leaving:
+
+
+
+
2-C fatty acid CoA* 7 acetyl CoA
+
The shorter fatty acid enters the pathway
and the cycle repeats, releasing more
hydrogens with their electrons and more
acetyl CoA. The molecules of acetyl CoA
enter the TCA cycle, and the coenzymes
carry the hydrogens and their electrons
to the electron transport chain.
C
C C
C
C
C
C
C
C
C
C
C
C
C
C
C
H
H
H
O
C
C C
C
C
C
C
C
C
C
C
C
C
C
C
C CoA
CoA
CoA
H
H
H
O
C
C C
C
C
C
C
C
C
C
C
C
C
C CoA CoA
+ C C
The fatty acid is first activated by
coenzyme A.
As each carbon-carbon bond is cleaved,
hydrogens and their electrons are released,
and coenzymes pick them up.
*Notice that 2-C fatty acid CoA = acetyl CoA, so that the final yield from a 16-C fatty acid is
8 acetyl CoA.
FIGURE 7-10 Animated! Fatty Acid-to-Acetyl CoA
Fatty acids are broken apart into 2-carbon fragments that combine with CoA to make acetyl CoA.
To test your understanding of
these concepts, log on to academic
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The body can convert the small glycerol portion of a triglyceride to either pyru-
vate (and then glucose) or acetyl CoA. The fatty acids of a triglyceride, on the
other hand, cannot make glucose, but they can provide abundant acetyl CoA.
Acetyl CoA may then enter the TCA cycle to release energy or combine with
other molecules of acetyl CoA to make body fat.
IN SUMMARY
The significance of fatty acids not being able to make glucose is that red blood cells
and the brain and nervous system depend primarily on glucose as fuel. Remember
that almost all dietary fats are triglycerides and that triglycerides contain only one
small molecule of glycerol with three fatty acids. The glycerol can yield glucose, ◆ but
that represents only 3 of the 50 or so carbon atoms in a triglyceride—about 5 percent
of its weight (see Figure 7-12). The other 95 percent cannot be converted to glucose.
◆ Reminder: The making of glucose from non-
carbohydrate sources is called gluconeogene-
sis. The glycerol portion of a triglyceride and
most amino acids can be used to make glu-
cose (review Figure 7-8, p. 221). The liver is
the major site of gluconeogenesis, but the
kidneys become increasingly involved under
certain circumstances, such as starvation.

224 • CHAPTER 7
Carbon
dioxide
C
Glucose
C C C
C
C C
Pyruvate
C
C C
C
C
C
C
C
C
C
C
C
C
C
C
C
C
C
C
Fatty acids
C C
C
C
C
C
C
C
C
C
C
C
C
C
C
C C
Glycerol
CoA
CoA
CoA
CoA
CoA
CoA
CoA
CoA
CoA
Fat (triglycerides)
C
C
C
C C C C C C C C
C
C
C
C
C
C
C
C
C C C C C C C C
C
C
C
C
C
C
C
C
C C C C C C C C
C
C
C
C
C
C
C
C
C C CoA
C C
Coenzyme
e–
H+
Coenzyme
e–
H+
To Electron
Transport
Chain
Acetyl CoA
CoA
To TCA Cycle
Glycerol enters the glycolysis pathway about midway between glucose and pyruvate and can be converted to either. Fatty acids
are broken down into 2-carbon fragments that combine with CoA to form acetyl CoA (shown in Figure 7-10). Result: a 16-carbon
fatty acid yields 8 acetyl CoA.
FIGURE 7-11 Animated! Fats Enter the Energy Pathway
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C
C
C
Glycerol
3 C
Fatty acids
54 C
18 C
18 C
18 C
C C C C C C C C C
C
C
C
C
C
C
C
C
C
C C C C C C C C C
C
C
C
C
C
C
C
C
C
C C C C C C C C C
C
C
C
C
C
C
C
C
C
A typical triglyceride contains only one small molecule of glycerol (3 C) but has three fatty acids
(each commonly 16 C or 18 C, or about 48 C to 54 C in total). Only the glycerol portion of a
triglyceride can yield glucose.
FIGURE 7-12 The Carbons of a Typical Triglyceride
Amino Acids
The preceding two sections have described how the breakdown of carbohydrate
and fat produces acetyl CoA, which can enter the pathways that provide energy
for the body’s use. One energy-yielding nutrient remains: protein or, rather, the
amino acids of protein.

Amino Acids-to-Acetyl CoA Before entering the metabolic pathways, amino
acids are deaminated (that is, they lose their nitrogen-containing amino group)
and then they are catabolized in a variety of ways. As Figure 7-13 illustrates, some
amino acids can be converted to pyruvate, others are converted to acetyl CoA, and
still others enter the TCA cycle directly as compounds other than acetyl CoA.
Amino Acids-to-Glucose As you might expect, amino acids that are used to
make pyruvate can provide glucose, whereas those used to make acetyl CoA can
provide additional energy or make body fat but cannot make glucose. ◆ Amino
acids entering the TCA cycle directly can continue in the cycle and generate energy;
alternatively, they can generate glucose.4 Thus protein, unlike fat, is a fairly good
source of glucose when carbohydrate is not available.
Deamination When amino acids are metabolized for energy or used to make glu-
cose or fat, they must be deaminated first. Two products result from deamination.
One is the carbon structure without its amino group—often a keto acid (see Figure
7-14, p. 226). The other product is ammonia (NH3), a toxic compound chemically
identical to the strong-smelling ammonia in bottled cleaning solutions. Ammonia
is a base, and if the body produces larger quantities than it can handle, the blood’s
critical acid-base balance becomes upset.
Transamination As the discussion of protein in Chapter 6 pointed out, only
some amino acids are essential; others can be made in the body, given a source of
nitrogen. By transferring an amino group from one amino acid to its correspon-
ding keto acid, cells can make a new amino acid and a new keto acid, as shown
in Figure 7-15 (p. 226). Through many such transamination reactions, involv-
ing many different keto acids, the liver cells can synthesize the nonessential
amino acids.
Ammonia-to-Urea in the Liver The liver continuously produces small amounts
of ammonia in deamination reactions. Some of this ammonia provides the nitrogen
NOTE: The arrows from pyruvate and the TCA cycle to amino acids are possible only for nonessential amino acids; remember, the
body cannot make essential amino acids.
Coenzyme
Coenzyme
e–
H+
To TCA Cycle
To Electron
Transport
Chain
Carbon
dioxide
C
Acetyl CoA
C C
C C
C
Amino acids
Most amino acids
can be used to
synthesize glucose;
they are glucogenic.
Some amino acids
are converted directly
to acetyl CoA; they are
ketogenic.
Some amino acids
can enter the TCA
cycle directly;
they are glucogenic.
CoA
Pyruvate
CoA
NH2
NH2
N
C C
C
NH2
N
C C
C
C
C
C
NH2
NH2
N
C
C C
C
FIGURE 7-13 Amino Acids Enter the Energy Pathway
keto (KEY-toe) acid: an organic acid that
contains a carbonyl group (C=O).
ammonia: a compound with the chemical
formula NH3; produced during the
deamination of amino acids.
transamination (TRANS-am-ih-NAY-shun):
the transfer of an amino group from one
amino acid to a keto acid, producing a new
nonessential amino acid and a new keto
acid.
◆ Amino acids that can make glucose via
either pyruvate or TCA cycle intermediates
are glucogenic; amino acids that are
degraded to acetyl CoA are ketogenic.

226 • CHAPTER 7
needed for the synthesis of nonessential amino acids (review Figure 7-14). The liver
quickly combines any remaining ammonia with carbon dioxide to make urea, a
much less toxic compound. Figure 7-16 provides a greatly oversimplified diagram of
urea synthesis; details are shown in Appendix C.
Urea Excretion via the Kidneys Liver cells release urea into the blood, where it
circulates until it passes through the kidneys (see Figure 7-17). The kidneys then re-
move urea from the blood for excretion in the urine. Normally, the liver efficiently
captures all the ammonia, makes urea from it, and releases the urea into the blood;
then the kidneys clear all the urea from the blood. This division of labor allows easy
diagnosis of diseases of both organs. In liver disease, blood ammonia will be high;
in kidney disease, blood urea will be high.
Urea is the body’s principal vehicle for excreting unused nitrogen, and the
amount of urea produced increases with protein intake. To keep urea in solution,
the body needs water. For this reason, a person who regularly consumes a high-
protein diet (say, 100 grams a day or more) must drink plenty of water to dilute and
excrete urea from the body. Without extra water, a person on a high-protein diet
risks dehydration because the body uses its water to rid itself of urea. This explains
some of the water loss that accompanies high-protein diets. Such losses may make
high-protein diets appear to be effective, but water loss, of course, is of no value to
the person who wants to lose body fat (as Highlight 9 explains).
FIGURE 7-14 Deamination and Synthe-
sis of a Nonessential Amino Acid
C NH2
H
COOH
C
COOH
O C NH2
H
COOH
C
COOH
O
Amino acid B
Keto acid A Amino acid A Keto acid B
+ +
Side
group
Side
group
Side
group
Side
group
The body can transfer amino groups (NH2) from an amino acid to a keto acid, forming
a new nonessential amino acid and a new keto acid. Transamination reactions require
the vitamin B6 coenzyme.
FIGURE 7-15 Transamination and Synthesis of a Nonessential Amino Acid
H N
H
C
O
N
H
+ +
Ammonia Ammonia
Carbon
dioxide
H
O
H
H O H
C
O
N H
N
H
H H
Urea
Water
H
FIGURE 7-16 Urea Synthesis
When amino acids are deaminated,
ammonia is produced. The liver detoxi-
fies ammonia before releasing it into the
bloodstream by combining it with
another waste product, carbon dioxide,
to produce urea. See Appendix C for
details.
The body can use some amino acids to produce glucose, whereas others can be
used either to generate energy or to make fat. Before an amino acid enters any
of these metabolic pathways, its nitrogen-containing amino group must be re-
moved through deamination. Deamination, which produces ammonia (NH3),
may be used to make nonessential amino acids and other nitrogen-containing
compounds; the rest is cleared from the body via urea synthesis in the liver
and excretion via the kidneys.
IN SUMMARY
Breaking Down Nutrients for Energy—
In Summary
To review the ways the body can use the energy-yielding nutrients, see the summary
table (p. 227). To obtain energy, the body uses glucose and fatty acids as its primary
fuels and amino acids to a lesser extent. To make glucose, the body can use all car-
bohydrates and most amino acids, but it can convert only 5 percent of fat (the glyc-
erol portion) to glucose. To make proteins, the body needs amino acids. It can use
glucose to make some nonessential amino acids when nitrogen is available; it can-
not use fats to make body proteins. Finally, when energy is consumed beyond the
body’s needs, all three energy-yielding nutrients can contribute to body fat stores.
urea (you-REE-uh): the principal nitrogen-
excretion product of protein metabolism.
Two ammonia fragments are combined with
carbon dioxide to form urea.
C NH2
H
COOH
C
COOH
NH3
O
Amino acid Keto acid
The deamination of an amino acid
produces ammonia (NH3) and a keto acid.
C NH2
H
COOH
C
COOH
NH3
O
Keto acid Amino acid
Given a source of NH3, the body can make
nonessential amino acids from keto acids.
Side
group
Side
group
Side
group
Side
group

Bloodstream
Liver
(NH3)
+
CO2
Urea
Bloodstream
Urea
Kidney
To bladder and
out of body
Urea
Ammonia
Amino acids
FIGURE 7-17 Urea Excretion
The liver and kidneys both play a role in
disposing of excess nitrogen. Can you see
why the person with liver disease has
high blood ammonia, whereas the per-
son with kidney disease has high blood
urea? (Figure 12-2 provides details of
how the kidneys work.)
Yields Amino
Yields Acids and Body Yields Fat
Nutrient Energy? Yields Glucose? Proteins? Stores?a
Carbohydrates Yes Yes Yes—when Yes
(glucose) nitrogen is
available, can
yield nonessential
amino acids
Lipids (fatty acids) Yes No No Yes
Lipids (glycerol) Yes Yes—when Yes—when Yes
carbohydrate is nitrogen is
unavailable available, can
yield nonessential
amino acids
Proteins (amino Yes Yes—when Yes Yes
acids) carbohydrate is
unavailable
aWhen energy intake exceeds needs, any of the energy-yielding nutrients can contribute to body fat stores.
IN SUMMARY
The Final Steps of Catabolism
Thus far the discussion has followed each of the energy-yielding nutrients down
three different pathways. All lead to the point where acetyl CoA enters the TCA cy-
cle. The TCA cycle reactions take place in the inner compartment of the mitochon-
dria. Examine the structure of the mitochondria shown in Figure 7-1 (p. 214). The
significance of its structure will become evident as details unfold.
The TCA Cycle Acetyl CoA enters the TCA cycle, a busy metabolic traffic center.
The TCA cycle is called a cycle, but that doesn’t mean it regenerates acetyl CoA.
Acetyl CoA goes one way only—down to two carbon dioxide molecules and a coen-
zyme (CoA). The TCA cycle is a circular path, though, in the sense that a 4-carbon
compound known as oxaloacetate is needed in the first step and synthesized in
the last step.
Oxaloacetate’s role in replenishing the TCA cycle is critical. When oxaloacetate
is insufficient, the TCA cycle slows down, and the cells face an energy crisis. Ox-
aloacetate is made primarily from pyruvate, although it can also be made from
certain amino acids. Importantly, oxaloacetate cannot be made from fat. That ox-
aloacetate must be available for acetyl CoA to enter the TCA cycle underscores the
importance of carbohydrates in the diet. A diet that provides ample carbohydrate
ensures an adequate supply of oxaloacetate (because glucose produces pyruvate
during glycolysis). (Highlight 9 presents more information on the consequences of
low-carbohydrate diets.)
As Figure 7-18 shows, oxaloacetate is the first 4-carbon compound to enter the
TCA cycle. Oxaloacetate picks up acetyl CoA (a 2-carbon compound), drops off one
carbon (as carbon dioxide), then another carbon (as carbon dioxide), and returns
to pick up another acetyl CoA. As for the acetyl CoA, its carbons go only one way—
to carbon dioxide (see Appendix C for additional details).*
* Actually, the carbons that enter the cycle in acetyl CoA may not be the exact ones that are given off
as carbon dioxide. In one of the steps of the cycle, a 6-carbon compound of the cycle becomes symmet-
rical, both ends being identical. Thereafter it loses carbons to carbon dioxide at one end or the other.
Thus only half of the carbons from acetyl CoA are given off as carbon dioxide in any one turn of the
cycle; the other half become part of the compound that returns to pick up another acetyl CoA. It is true
to say, though, that for each acetyl CoA that enters the TCA cycle, 2 carbons are given off as carbon
dioxide. It is also true that with each turn of the cycle, the energy equivalent of one acetyl CoA is
released.
oxaloacetate (OKS-ah-low-AS-eh-tate): a
carbohydrate intermediate of the TCA cycle.

228 • CHAPTER 7
As acetyl CoA molecules break down to carbon dioxide, hydrogen atoms with
their electrons are removed from the compounds in the cycle. Each turn of the TCA
cycle releases a total of eight electrons. Coenzymes made from the B vitamins
niacin and riboflavin receive the hydrogens and their electrons from the TCA cycle
and transfer them to the electron transport chain—much like a taxi cab that picks
up passengers in one location and drops them off in another.
C
C C
C
C C C
C
C C
C
C C
C
C C
C
C C
C
C C C C
C
C C C
C
C C C
C
C C C
C
C C C
C
C
C
Pyruvate
(from carbon
dioxide)
C
(as carbon
dioxide)
(as carbon
dioxide)
To Electron
Transport
Chain
To Electron
Transport
Chain
(as carbon
dioxide)
Yields energy
(captured in high-energy
compound similar to ATP)
Oxaloacetate
Coenzyme
Coenzyme
e–
H+
Coenzyme
Coenzyme
e–
H+
Coenzyme
Coenzyme
e–
H+
Coenzyme
Coenzyme
e–
H+
CoA
C
C
Acetyl CoA
CoA
NOTE: Knowing that glucose produces pyruvate during glycolysis and that oxaloacetate must be available to start the TCA cycle, you can understand
why the complete oxidation of fat requires carbohydrate.
FIGURE 7-18 Animated! The TCA Cycle
Oxaloacetate, a compound made primarily from pyruvate, starts the TCA cycle. The 4-carbon oxaloacetate joins with the 2-carbon acetyl
CoA to make a 6-carbon compound. This compound is changed a little to make a new 6-carbon compound, which releases carbons as car-
bon dioxide, becoming a 5- and then a 4-carbon compound. Each reaction changes the structure slightly until finally the original 4-carbon
oxaloacetate forms again and picks up another acetyl CoA—from the breakdown of glucose, glycerol, fatty acids, and amino acids—and
starts the cycle over again. The breakdown of acetyl CoA releases hydrogens with their electrons, which are carried by coenzymes made
from the B vitamins niacin and riboflavin to the electron transport chain. (For more details, see Appendix C.)
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The Electron Transport Chain In the final pathway, the electron transport
chain, energy is captured in the high-energy bonds of ATP. The electron transport
chain consists of a series of proteins that serve as electron “carriers.” These carriers
are mounted in sequence on the inner membrane of the mitochondria (review Fig-
ure 7-1 on p. 214). As the coenzymes deliver their electrons from the TCA cycle, gly-
colysis, and fatty acid oxidation to the electron transport chain, each carrier receives
the electrons and passes them on to the next carrier. These electron carriers continue
passing the electrons down until they reach oxygen at the end of the chain. Oxygen
(O) accepts the electrons and combines with hydrogen atoms (H) to form water
(H2O). ◆ That oxygen must be available for energy metabolism explains why it is
essential to life.
As electrons are passed from carrier to carrier, enough energy is released to
pump hydrogen ions across the membrane to the outer compartment of the mito-
chondria. The rush of hydrogen ions back into the inner compartment powers the
synthesis of ATP. In this way, energy is captured in the bonds of ATP. The ATP leaves
the mitochondria and enters the cytoplasm, where it can be used for energy. Figure
7-19 provides a simple diagram of the electron transport chain (see Appendix C for
details).
The kCalories-per-Gram Secret Revealed Of the three energy-yielding nutri-
ents, fat provides the most energy per gram. ◆ The reason may be apparent in Fig-
ure 7-20 (p. 230), which compares a fatty acid with a glucose molecule. Notice that
nearly all the bonds in the fatty acid are between carbons and hydrogens. Oxygen
can be added to all of them (forming carbon dioxide with the carbons and water
with the hydrogens). As this happens, hydrogens are released to coenzymes heading
◆ The results of the electron transport chain:
• O2 consumed
• H2O and CO2 produced
• Energy captured in ATP
FIGURE 7-19 Animated! Electron Transport Chain and ATP Synthesis
Electron Transport Chain
Outer compartment
Electron
carrier
Water
ADP ATP
P
+
+
ATP Synthesis
Passing electrons from carrier to
carrier along the chain releases
enough energy to pump
hydrogen ions across the
membrane.
Hydrogen ions flow “downhill”—from
an area of high concentration to an
area of low concentration—through
a special protein complex that
powers the synthesis of ATP.
Coenzymes deliver hydrogens
and high-energy electrons to the
electron transport chain from the
TCA cycle.
Inner compartment Hydrogens
+
Oxygen
Oxygen accepts
the electrons and
combines with
hydrogens to
form water. A P P P
A P P P
H+
H+
H+
H+
H+
H+
H+
H+
H+
H+
H+ H+
H+
H+
H+
H+
H+
H+
H+
H+
H+
H+
H+
H+
H+
H+
H+
H+
H+
H+
Coenzymes
Electron
carrier
Electron
carrier
Electron
carrier
e–
Inner membrane
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◆ Fat = 9 kcal/g
Carbohydrate = 4 kcal/g
Protein = 4 kcal/g

230 • CHAPTER 7
for the electron transport chain. In glucose, on the other hand, an oxygen is already
bonded to each carbon. Thus there is less potential for oxidation, and fewer hydro-
gens are released when the remaining bonds are broken.
Because fat contains many carbon-hydrogen bonds that can be readily oxidized,
it sends numerous coenzymes with their hydrogens and electrons to the electron
transport chain where that energy can be captured in the bonds of ATP. This ex-
plains why fat yields more kcalories per gram than carbohydrate or protein. (Re-
member that each ATP holds energy and that kcalories measure energy; thus the
more ATP generated, the more kcalories have been collected.) For example, one glu-
cose molecule will yield 30 to 32 ATP when completely oxidized.5 In comparison,
one 16-carbon fatty acid molecule will yield 129 ATP when completely oxidized. Fat
is a more efficient fuel source. Gram for gram, fat can provide much more energy
than either of the other two energy-yielding nutrients, making it the body’s preferred
form of energy storage. (Similarly, you might prefer to fill your car with a fuel that
provides 130 miles per gallon versus one that provides 30 miles per gallon.)
FIGURE 7-20 Chemical Structures of a Fatty Acid and Glucose Compared
To ease comparison, the structure shown here for glucose is not the ring structure shown in Chapter 4, but an alternative way of
drawing its chemical structure.
C
H
H
H
C
H
H
C
H
H
C
H
H
C
H
H
C
H
H
C
H
H
C
H
H
C
H
H
C
H
H
C
H
H
C
H
H
C
H
H
C
H
H
C
H
H
C
O
OH
Fatty acid Glucose
C
H
OH
C
H
OH
C
OH
H
C
H
OH
HOCH2 C
O
H
After a balanced meal, the body handles the nutrients as follows. The diges-
tion of carbohydrate yields glucose (and other monosaccharides); some is
stored as glycogen, and some is broken down to pyruvate and acetyl CoA to
provide energy. The acetyl CoA can then enter the TCA cycle and electron
transport chain to provide more energy. The digestion of fat yields glycerol
and fatty acids; some are reassembled and stored as fat, and others are broken
down to acetyl CoA, which can enter the TCA cycle and electron transport
chain to provide energy. The digestion of protein yields amino acids, most of
which are used to build body protein or other nitrogen-containing com-
pounds, but some amino acids may be broken down through the same path-
ways as glucose to provide energy. Other amino acids enter directly into the
TCA cycle, and these, too, can be broken down to yield energy.
IN SUMMARY
In summary, although carbohydrate, fat, and protein enter the TCA cycle by differ-
ent routes, the final pathways are common to all energy-yielding nutrients. These
pathways are all shown in Figure 7-21. Instead of dismissing this figure as “too
busy,” take a few moments to appreciate the busyness of it all. Consider that this fig-
ure is merely an overview of energy metabolism, and then imagine how busy a cell
really is during the metabolism of hundreds of compounds, each of which may be
involved in several reactions, each requiring an enzyme.
Energy Balance
Every day, a healthy diet delivers over a thousand kcalories from foods, and the ac-
tive body uses most of them to do its work. As a result, body weight changes little, if
at all. Maintaining body weight reflects that the body’s energy budget is balanced.

FIGURE 7-21 The Central Pathways of Energy Metabolism
In reviewing these pathways, notice that:
• All of the energy-yielding nutrients—protein, carbohydrates, and fat—can be broken down to acetyl CoA, which can enter the TCA cycle.
• Many of these reactions release hydrogen atoms with their electrons, which are carried by coenzymes to the electron transport
chain, where ATP is synthesized.
• In the end, oxygen is consumed, water and carbon dioxide are produced, and energy is captured in ATP.
C C
C
C Carbon dioxide
Carbohydrates
Amino acids
Carbon dioxide
+ Oxygen H2O
CoA
Carbon
dioxide
C
Glucose
C C C
C
C C
Pyruvate
C
C C C
C
C
C
C
C
C
C
C
C
C
C
C
C
C
C
Fatty acids
C
C C
Glycerol
CoA
Fat (triglycerides)
C
C
C
C C C C C C C C
C
C
C
C
C
C
C
C
C C C C C C C C
C
C
C
C
C
C
C
C
C C C C C C C C
C
C
C
C
C
C
C
C
Coenzyme
e–
H+
Coenzyme
e–
H+
Coenzyme
e–
H+
Coenzyme
e–
H+
H+
H+
H+
H+
Coenzyme
e–
H+
H+
H+
A P P P
A P P
Acetyl CoA
CoA
TCA Cycle
Coenzyme
e–
H+
Coenzyme
e–
H+
Coenzyme
e–
H+
NH2
NH2
N
C C
C
NH2
N
C C
C
C
C
C
NH2
NH2
N
C
C C
C
Electron Transport Chain
C C
C
C
CoA
C C CoA
C C CoA
C
C
CoA
C
C
CoA
CoA
CoA
C
C
CoA
C
C
CoA

232 • CHAPTER 7
Some people, however, eat too much or exercise too little and get fat; others eat too
little or exercise too much and get thin. The metabolic details have already been de-
scribed; the next sections review them from the perspective of the body fat gained or
lost. The possible reasons why people gain or lose weight are explored in Chapter 8.
Feasting—Excess Energy
When a person eats too much, metabolism favors fat formation. Fat cells enlarge re-
gardless of whether the excess in kcalories derives from protein, carbohydrate, or fat.
The pathway from dietary fat to body fat, however, is the most direct (requiring only
a few metabolic steps) and the most efficient (costing only a few kcalories). To con-
vert a dietary triglyceride to a triglyceride in adipose tissue, the body removes two of
the fatty acids from the glycerol backbone, absorbs the parts, and puts them (and
others) together again. By comparison, to convert a molecule of sucrose, the body
has to split glucose from fructose, absorb them, dismantle them to pyruvate and
acetyl CoA, assemble many acetyl CoA molecules into fatty acid chains, and finally
attach fatty acids to a glycerol backbone to make a triglyceride for storage in adi-
pose tissue. Quite simply, the body uses much less energy to convert dietary fat to
body fat than it does to convert dietary carbohydrate to body fat. On average, stor-
ing excess energy from dietary fat as body fat uses only 5 percent of the ingested en-
ergy intake, but storing excess energy from dietary carbohydrate as body fat requires
25 percent of the ingested energy intake.
The pathways from excess protein and excess carbohydrate to body fat are not
only indirect and inefficient, but they are also less preferred by the body (having
other priorities for using these nutrients). Before entering fat storage, protein must
first tend to its many roles in the body’s lean tissues, and carbohydrate must fill the
glycogen stores. Simply put, using these two nutrients to make fat is a low priority
for the body. Still, if eaten in abundance, any of the energy-yielding nutrients can
be made into fat.
This chapter has described each of the energy-yielding nutrients individually,
but cells use a mixture of these fuels. How much of which nutrient is in the fuel
mix depends, in part, on its availability from the diet. (The proportion of each fuel
also depends on physical activity.) Dietary protein and dietary carbohydrate influ-
ence the mixture of fuel used during energy metabolism. Usually, protein’s contri-
bution to the fuel mix is relatively minor and fairly constant, but protein
oxidation does increase when protein is eaten in excess. Similarly, carbohydrate
eaten in excess significantly enhances carbohydrate oxidation. In contrast, fat ox-
idation does not respond to dietary fat intake, especially when dietary changes oc-
cur abruptly. The more protein or carbohydrate in the fuel mix, the less fat
contributes to the fuel mix. Instead of being oxidized, fat accumulates in storage.
Details follow.
Excess Protein Recall from Chapter 6 that the body cannot store excess amino
acids as such; it has to convert them to other compounds. Contrary to popular opin-
ion, a person cannot grow muscle simply by overeating protein. Lean tissue such as
muscle develops in response to a stimulus such as hormones or physical activity.
When a person overeats protein, the body uses the surplus first by replacing normal
daily losses and then by increasing protein oxidation. The body achieves protein
balance this way, but any increase in protein oxidation displaces fat in the fuel mix.
Any additional protein is then deaminated and the remaining carbons are used to
make fatty acids, which are stored as triglycerides in adipose tissue. Thus a person
can grow fat by eating too much protein.
People who eat huge portions of meat and other protein-rich foods may wonder
why they have weight problems. Not only does the fat in those foods lead to fat
storage, but the protein can, too, when energy intake exceeds energy needs. Many
fad weight-loss diets encourage high protein intakes based on the false assumption
that protein builds only muscle, not fat (see Highlight 9 for more details).
People can enjoy bountiful meals such as this
without storing body fat, provided that they
expend as much energy as they take in. ©
Jeff
Greenberg/PhotoEdit

Excess Carbohydrate Compared with protein, the proportion of carbohydrate in
the fuel mix changes more dramatically when a person overeats. The body handles
abundant carbohydrate by first storing it as glycogen, but glycogen storage areas
are limited and fill quickly. Because maintaining glucose balance is critical, the
body uses glucose frugally when the diet provides only small amounts and freely
when stores are abundant. In other words, glucose oxidation rapidly adjusts to the
dietary intake of carbohydrate.
Excess glucose can also be converted to fat directly, but this is a minor pathway.6
As mentioned earlier, converting glucose to fat is energetically expensive and does
not occur until after glycogen stores have been filled. Even then, only a little, if any,
new fat is made from carbohydrate.7
Nevertheless, excess dietary carbohydrate can lead to weight gain when it dis-
places fat in the fuel mix. When this occurs, carbohydrate spares both dietary fat
and body fat from oxidation—an effect that may be more pronounced in over-
weight people than in lean people.8 The net result: excess carbohydrate contributes
to obesity or at least to the maintenance of an overweight body.
Excess Fat Unlike excess protein and carbohydrate, which both enhance their
own oxidation, eating too much fat does not promote fat oxidation.9 Instead, excess
dietary fat moves efficiently into the body’s fat stores; almost all of the excess is
stored.
If energy intake exceeds the body’s energy needs, the result will be weight
gain—regardless of whether the excess intake is from protein, carbohydrate,
or fat. The difference is that the body is much more efficient at storing energy
when the excess derives from dietary fat.
IN SUMMARY
The Transition from Feasting to Fasting
Figure 7-22 (p. 234) shows the metabolic pathways operating in the body as it shifts
from feasting (part A) to fasting (parts B and C). After a meal, glucose, glycerol, and
fatty acids from foods are used as needed and then stored. Later, as the body shifts
from a fed state to a fasting one, it begins drawing on these stores. Glycogen and fat
are released from storage to provide more glucose, glycerol, and fatty acids for energy.
Energy is needed all the time. Even when a person is asleep and totally relaxed,
the cells of many organs are hard at work. In fact, this work—the cells’ work that
maintains all life processes ◆ without any conscious effort—represents about two-
thirds of the total energy a person spends in a day. The small remainder is the work
that a person’s muscles perform voluntarily during waking hours.
The body’s top priority is to meet the cells’ needs for energy, and it normally does
this by periodic refueling—that is, by eating several times a day. When food is not
available, the body turns to its own tissues for other fuel sources. If people choose
not to eat, we say they are fasting; if they have no choice, we say they are starving.
The body makes no such distinction. In either case, the body is forced to draw on its
reserves of carbohydrate and fat and, within a day or so, on its vital protein tissues
as well.
Fasting—Inadequate Energy
During fasting, carbohydrate, fat, and protein are all eventually used for energy—
fuel must be delivered to every cell. As the fast begins, glucose from the liver’s stored
glycogen and fatty acids from the adipose tissue’s stored fat are both flowing into
◆ The cells’ work that maintains all life
processes refers to the body’s basal
metabolism, which is described in Chapter 8.

234 • CHAPTER 7
cells, then breaking down to yield acetyl CoA, and finally delivering energy to power
the cells’ work. Several hours later, however, most of the glucose is used up—liver
glycogen is exhausted and blood glucose begins to fall. Low blood glucose serves as a
signal that promotes further fat breakdown and release of amino acids from muscles.
Glucose Needed for the Brain At this point, most of the cells are depending on
fatty acids to continue providing their fuel. But red blood cells and the cells of the
nervous system need glucose. Glucose is their primary energy fuel, and even when
other energy fuels are available, glucose must be present to permit the energy-
metabolizing machinery of the nervous system to work. Normally, the brain and
nerve cells—which weigh only about three pounds—consume about half of the to-
tal glucose used each day (about 500 kcalories’ worth). About one-fourth of the en-
ergy the adult body uses when it is at rest is spent by the brain; in children, it can be
up to one-half.
Protein Meets Glucose Needs The red blood cells’ and brain’s special require-
ments for glucose pose a problem for the fasting body. The body can use its stores of
fat, which may be quite generous, to furnish most of its cells with energy, but the red
blood cells are completely dependent on glucose, ◆ and the brain and nerves prefer
energy in the form of glucose. Amino acids that yield pyruvate can be used to make
glucose, and to obtain the amino acids, body proteins must be broken down. For this
reason, body protein tissues such as muscle and liver always break down to some ex-
tent during fasting. The amino acids that can’t be used to make glucose are used as
an energy source for other body cells.
The breakdown of body protein is an expensive way to obtain glucose. In the
first few days of a fast, body protein provides about 90 percent of the needed glu-
FIGURE 7-22 Feasting and Fasting
Component to
be broken down:
Broken down in
the body to:
And then
used for:
When a person overeats (feasting):
A.
When a person eats in excess of energy
needs, the body stores a small amount
of glycogen and much larger quantities
of fat.
When a person draws on stores
(fasting):
If the fast continues beyond
glycogen depletion:
As glycogen stores dwindle (after about
24 hours of starvation), the body begins
to break down its protein (muscle and
lean tissue) to amino acids to synthesize
glucose needed for brain and nervous
system energy. In addition, the liver
converts fats to ketone bodies, which
serve as an alternative energy source for
the brain, thus slowing the breakdown of
body protein.
Carbohydrate Glucose Liver and muscle
glycogen stores
Fat
Protein
Fatty acids Body fat stores
Amino acids
Body proteins
Liver and muscle
glycogen storesa
Body fat stores
Glucose
Fatty acids
Body fat
Amino
acids
Fatty
acids
Glucose
Ketone
bodies
Body protein
Energy for the brain,
nervous system, and
red blood cells
Energy for other cells
Loss of nitrogen
in urine (urea)
Energy for the brain
and nervous system
Energy for other cells
a
The muscles’ stored glycogen provides glucose only for the muscle in which the glycogen is stored.
When nutrients from a meal are no longer
available to provide energy (about 2 to 3
hours after a meal), the body draws on its
glycogen and fat stores for energy.
B.
C.
Loss of nitrogen
in urine (urea)
◆ Red blood cells contain no mitochondria.
Review Figure 7-1 (p. 214) to fully appreciate
why red blood cells must depend on glucose
for energy.

cose; glycerol, about 10 percent. If body protein losses were to continue at this rate,
death would ensue within three weeks, regardless of the quantity of fat a person
had stored. Fortunately, fat breakdown also increases with fasting—in fact, fat
breakdown almost doubles, providing energy for other body cells and glycerol for
glucose production.
The Shift to Ketosis As the fast continues, the body finds a way to use its fat to
fuel the brain. It adapts by combining acetyl CoA fragments derived from fatty acids
to produce an alternate energy source, ketone bodies (Figure 7-23). Normally pro-
duced and used only in small quantities, ketone bodies ◆ can provide fuel for some
brain cells. Ketone body production rises until, after about ten days of fasting, it is
meeting much of the nervous system’s energy needs. Still, many areas of the brain
rely exclusively on glucose, and to produce it, the body continues to sacrifice pro-
tein—albeit at a slower rate than in the early days of fasting.
When ketone bodies contain an acid group (COOH), they are called keto acids.
Small amounts of keto acids are a normal part of the blood chemistry, but when
their concentration rises, the pH of the blood drops. This is ketosis, a sign that the
body’s chemistry is going awry. Elevated blood ketones (ketonemia) are excreted in
the urine (ketonuria). A fruity odor on the breath (known as acetone breath) devel-
ops, reflecting the presence of the ketone acetone.
Suppression of Appetite Ketosis also induces a loss of appetite. As starvation
continues, this loss of appetite becomes an advantage to a person without access to
food, because the search for food would be a waste of energy. When the person finds
food and eats again, the body shifts out of ketosis, the hunger center gets the message
that food is again available, and the appetite returns. Highlight 9 includes a discus-
sion of the risks of ketosis-producing diets in its review of popular weight-loss diets.
Slowing of Metabolism In an effort to conserve body tissues for as long as pos-
sible, the hormones of fasting slow metabolism. As the body shifts to the use of ke-
tone bodies, it simultaneously reduces its energy output and conserves both its fat
and its lean tissue. Still the lean (protein-containing) organ tissues shrink in mass
and perform less metabolic work, reducing energy expenditures. As the muscles
waste, they can do less work and so demand less energy, reducing expenditures fur-
ther. Although fasting may promote dramatic weight loss, a low-kcalorie diet better
supports fat loss while retaining lean tissue.
◆ Reminder: Ketone bodies are compounds pro-
duced during the incomplete breakdown of
fat when glucose is not available.
FIGURE 7-23 Ketone Body Formation
C C
H
H O
H
CoA + C C
H
H O
H
CoA + H2O
C C
H
H O
H
C C
H O
H
OH
A ketone, acetoacetate
C C
H
H O
H
C H
H
H
A ketone, acetone
CO2
2 CoA
Acetyl CoA Acetyl CoA
The first step in the
formation of ketone bodies
is the condensation of two
molecules of acetyl CoA
and the removal of the CoA
to form a compound that is
converted to the first
ketone body.
This ketone body may lose a
molecule of carbon dioxide to
become another ketone.
Or, the acetoacetate may add
two hydrogens, becoming
another ketone body
(beta-hydroxybutyrate). See
Appendix C for more details.
1
2
3

236 • CHAPTER 7
Symptoms of Starvation The adaptations just described—slowing of energy
output and reduction in fat loss—occur in the starving child, the hungry homeless
adult, the fasting religious person, the adolescent with anorexia nervosa, and the
malnourished hospital patient. Such adaptations help to prolong their lives and ex-
plain the physical symptoms of starvation: wasting; slowed heart rate, respiration,
and metabolism; lowered body temperature; impaired vision; organ failure; and re-
duced resistance to disease.10 Psychological effects of food deprivation include de-
pression, anxiety, and food-related dreams.
The body’s adaptations to fasting are sufficient to maintain life for a long time—
up to two months. Mental alertness need not be diminished, and even some phys-
ical energy may remain unimpaired for a surprisingly long time. These remarkable
adaptations, however, should not prevent anyone from recognizing the very real
hazards that fasting presents.
When fasting, the body makes a number of adaptations: increasing the break-
down of fat to provide energy for most of the cells, using glycerol and amino
acids to make glucose for the red blood cells and central nervous system, pro-
ducing ketones to fuel the brain, suppressing the appetite, and slowing metab-
olism. All of these measures conserve energy and minimize losses.
IN SUMMARY
This chapter has probed the intricate details of metabolism at the level of the cells,
exploring the transformations of nutrients to energy and to storage compounds. Sev-
eral chapters and highlights build on this information. The highlight that follows this
chapter shows how alcohol disrupts normal metabolism. Chapter 8 describes how a
person’s intake and expenditure of energy are reflected in body weight and body com-
position. Chapter 9 examines the consequences of unbalanced energy budgets—over-
weight and underweight. Chapter 10 shows the vital roles the B vitamins play as
coenzymes assisting all the metabolic pathways described here.
All day, every day, your cells dismantle carbohydrates, fats, and proteins, with the help
of vitamins, minerals, and water, releasing energy to meet your body’s immediate
needs or storing it as fat for later use.
■ Describe what types of foods best support aerobic and anaerobic activities.
■ Consider whether you eat more protein, carbohydrate, or fat than your body
needs.
■ Explain how a low-carbohydrate diet forces your body into ketosis.
Nutrition Portfolio
These questions will help you review the chapter. You will
1. Define metabolism, anabolism, and catabolism; give an
example of each. (pp. 213–216)
2. Name one of the body’s high-energy molecules, and
describe how it is used. (pp. 216–217)
STUDY QUESTIONS

3. What are coenzymes, and what service do they provide
in metabolism? (p. 216)
4. Name the four basic units, derived from foods, that
are used by the body in metabolic transformations.
How many carbons are in the “backbones” of each?
(pp. 217–218)
5. Define aerobic and anaerobic metabolism. How does
insufficient oxygen influence metabolism? (pp. 220–221)
6. How does the body dispose of excess nitrogen?
(pp. 225–227)
7. Summarize the main steps in the metabolism of glucose,
glycerol, fatty acids, and amino acids. (pp. 226–228)
8. Describe how a surplus of the three energy nutrients
contributes to body fat stores. (pp. 219–226)
9. What adaptations does the body make during a fast?
What are ketone bodies? Define ketosis. (pp. 233–236)
10. Distinguish between a loss of fat and a loss of weight, and
describe how each might happen. (pp. 235–236)
exam. Answers can be found below.
1. Hydrolysis is an example of a(n):
a. coupled reaction.
b. anabolic reaction.
c. catabolic reaction.
d. synthesis reaction.
2. During metabolism, released energy is captured and
transferred by:
a. enzymes.
b. pyruvate.
c. acetyl CoA.
d. adenosine triphosphate.
3. Glycolysis:
a. requires oxygen.
b. generates abundant energy.
c. converts glucose to pyruvate.
d. produces ammonia as a by-product.
4. The pathway from pyruvate to acetyl CoA:
a. produces lactate.
b. is known as gluconeogenesis.
c. is metabolically irreversible.
d. requires more energy than it produces.
5. For complete oxidation, acetyl CoA enters:
a. glycolysis.
b. the TCA cycle.
c. the Cori cycle.
d. the electron transport chain.
6. Deamination of an amino acid produces:
a. vitamin B6 and energy.
b. pyruvate and acetyl CoA.
c. ammonia and a keto acid.
d. carbon dioxide and water.
7. Before entering the TCA cycle, each of the energy-
yielding nutrients is broken down to:
a. ammonia.
b. pyruvate.
c. electrons.
d. acetyl CoA.
8. The body stores energy for future use in:
a. proteins.
b. acetyl CoA.
c. triglycerides.
d. ketone bodies.
9. During a fast, when glycogen stores have been depleted,
the body begins to synthesize glucose from:
a. acetyl CoA.
b. amino acids.
c. fatty acids.
d. ketone bodies.
10. During a fast, the body produces ketone bodies by:
a. hydrolyzing glycogen.
b. condensing acetyl CoA.
c. transaminating keto acids.
d. converting ammonia to urea.
1. R. H. Garrett and C. M. Grisham, Biochem-
istry (Belmont, Calif.: Thomson Brooks/
Cole, 2005), p. 73.
2. R. A. Robergs, F. Ghiasvand, and D. Parker,
Biochemistry of exercise-induced metabolic
acidosis, American Journal of Physiology—
Regulatory, Integrative and Comparative Physi-
ology 287 (2004): R502–R516.
3. T. H. Pederson and coauthors, Intracellular
acidosis enhances the excitability of work-
ing muscle, Science 305 (2004): 1144–1147.
4. S. S. Gropper, J. L. Smith, and J. L. Groff,
Advanced Nutrition and Human Metabolism
(Belmont, Calif.: Wadsworth/Thomson
Learning, 2005), p. 198.
5. Garrett and Grisham, 2005, p. 669.
6. M. K. Hellerstein, No common energy
currency: De novo lipogenesis as the road
less traveled, American Journal of Clinical
Nutrition 74 (2001): 707–708.
7. R. M. Devitt and coauthors, De novo lipoge-
nesis during controlled overfeeding with
sucrose or glucose in lean and obese
women, American Journal of Clinical Nutrition
74 (2001): 707–708.
8. I. Marques-Lopes and coauthors, Postpran-
dial de novo lipogenesis and metabolic
changes induced by a high-carbohydrate,
low-fat meal in lean and overweight men,
(2001): 253–261.
9. E. J. Parks, Macronutrient Metabolism
Group Symposium on “Dietary fat: How low
should we go?” Changes in fat synthesis
influenced by dietary macronutrient con-
tent, Proceedings of the Nutrition Society 61
(2002): 281–286.
10. C. A. Jolly, Dietary restriction and immune
function, Journal of Nutrition 134 (2004):
1853–1856.
REFERENCES
1. c 2. d 3. c 4. c 5. b 6. c 7. d 8. c
9. b 10. b
ANSWERS

HIGHLIGHT 7
238
With the understanding of metabolism
gained from Chapter 7, you are in a position
to understand how the body handles alcohol,
how alcohol interferes with metabolism, and
how alcohol impairs health and nutrition. Be-
fore examining alcohol’s damaging effects, it
may be appropriate to mention that drinking
alcohol in moderation may have some health
benefits, including reduced risks of heart at-
tacks, strokes, dementia, diabetes, and osteoporosis.1 Moderate
alcohol consumption may lower mortality from all causes, but
only in adults age 35 and older.2 No health benefits are evident
before middle age.3 Importantly, any benefits of alcohol must be
weighed against the many harmful effects described in this high-
light, as well as the possibility of alcohol abuse.
Alcohol in Beverages
To the chemist, alcohol refers to a class of organic compounds
containing hydroxyl (OH) groups (the accompanying glossary
defines alcohol and related terms). The glycerol to which fatty
acids are attached in triglycerides is an example of an alcohol to a
chemist. To most people, though, alcohol refers to the intoxicat-
ing ingredient in beer, wine, and distilled liquor (hard
liquor). The chemist’s name for this particular alcohol is ethyl al-
cohol, or ethanol. Glycerol has 3 carbons with 3 hydroxyl groups
attached; ethanol has only 2 carbons and 1 hydroxyl group (see
Figure H7-1). The remainder of this highlight talks about the par-
ticular alcohol, ethanol, but refers to it simply as alcohol.
Alcohols affect living things profoundly, partly because they
act as lipid solvents. Their ability to dissolve lipids out of cell mem-
branes allows alcohols to penetrate rapidly into cells, destroying
cell structures and thereby killing the cells. For this reason, most
alcohols are toxic in relatively small amounts;
by the same token, because they kill microbial
cells, they are useful as disinfectants.
Ethanol is less toxic than the other alco-
hols. Sufficiently diluted and taken in small
enough doses, its action in the brain produces
an effect that people seek—not with zero risk,
but with a low enough risk (if the doses are
low enough) to be tolerable. Used in this way,
alcohol is a drug—that is, a substance that modifies body func-
tions. Like all drugs, alcohol both offers benefits and poses haz-
ards. The 2005 Dietary Guidelines advise “those who choose to
drink alcoholic beverages to do so sensibly and in moderation.”
FIGURE H7-1 Two Alcohols: Glycerol and Ethanol
C OH
H
H
C OH
H
C OH
H
H
H
C
H
C
H
OH
H
H
Glycerol is the
alcohol used
to make
triglycerides.
Ethanol is the
alcohol in beer,
wine, and
distilled liquor.
• Those who choose to drink alcoholic beverages
should do so sensibly and in moderation: up to
one drink per day for women and two drinks per
day for men.
The term moderation is important when describing alcohol
use. How many drinks constitute moderate use, and how much is
“a drink”? First, a drink is any alcoholic beverage that delivers 1/2
ounce of pure ethanol:
• 5 ounces of wine
• 10 ounces of wine cooler
• 12 ounces of beer
• 11/2 ounces of distilled liquor (80 proof whiskey, scotch,
rum, or vodka)
Beer, wine, and liquor deliver different amounts of alcohol. The
amount of alcohol in distilled liquor is stated as proof: 100 proof
liquor is 50 percent alcohol, 80 proof is 40 percent alcohol, and so
forth. Wine and beer have less alcohol than distilled liquor, although
some fortified wines and beers have more alcohol than the regular va-
rieties (see photo caption on p. 239).
Richard
Dunkley/Getty
Images
• Alcoholic beverages should not be consumed by some
individuals, including those who cannot restrict their alcohol
intake, women of childbearing age who may become
pregnant, pregnant and lactating women, children and ado-
lescents, individuals taking medications that can interact with
alcohol, and those with specific medical conditions.
• Alcoholic beverages should be avoided by individuals engag-
ing in activities that require attention, skill, or coordination,
such as driving or operating machinery.
Alcohol and Nutrition

ALCOHOL AND NUTRITION • 239
Second, because people have different tolerances for alcohol, it
is impossible to name an exact daily amount of alcohol that is appro-
priate for everyone. Authorities have attempted to identify amounts
that are acceptable for most healthy people. An accepted definition
of moderation is up to two drinks per day for men and up to one
5 oz wine
12 oz beer 10 oz wine cooler
1 oz liquor
(80 proof
whiskey, gin,
brandy,
rum, vodka)
1
2
Each of these servings equals one drink.
GLOSSARY
acetaldehyde (ass-et-AL-duh-
hide): an intermediate in
alcohol metabolism.
alcohol: a class of organic
compounds containing hydroxyl
(OH) groups.
alcohol abuse: a pattern of
drinking that includes failure to
fulfill work, school, or home
responsibilities; drinking in
situations that are physically
dangerous (as in driving while
intoxicated); recurring alcohol-
related legal problems (as in
aggravated assault charges); or
continued drinking despite
ongoing social problems that
are caused by or worsened by
alcohol.
alcohol dehydrogenase (dee-
high-DROJ-eh-nayz): an
enzyme active in the stomach
and the liver that converts
ethanol to acetaldehyde.
alcoholism: a pattern of drinking
that includes a strong craving
for alcohol, a loss of control and
an inability to stop drinking
once begun, withdrawal
symptoms (nausea, sweating,
shakiness, and anxiety) after
heavy drinking, and the need
for increasing amounts of
alcohol to feel “high.”
antidiuretic hormone (ADH): a
hormone produced by the
pituitary gland in response to
dehydration (or a high sodium
concentration in the blood). It
stimulates the kidneys to
reabsorb more water and
therefore prevents water loss in
urine (also called vasopressin).
(This ADH should not be
confused with the enzyme
alcohol dehydrogenase, which
is also sometimes abbreviated
ADH.)
beer: an alcoholic beverage
brewed by fermenting malt
and hops.
cirrhosis (seer-OH-sis): advanced
liver disease in which liver cells
turn orange, die, and harden,
permanently losing their
function; often associated with
alcoholism.
• cirrhos an orange
distilled liquor or hard liquor:
an alcoholic beverage made by
fermenting and distilling grains;
sometimes called distilled spirits.
drink: a dose of any alcoholic
beverage that delivers 1
⁄2 oz of
pure ethanol:
• 5 oz of wine
• 10 oz of wine cooler
• 12 oz of beer
• 11
⁄2 oz of hard liquor (80 proof
whiskey, scotch, rum, or vodka)
drug: a substance that can
modify one or more of the
body’s functions.
ethanol: a particular type of
alcohol found in beer, wine, and
distilled liquor; also called ethyl
alcohol (see Figure H7-1).
Ethanol is the most widely
used—and abused—drug in our
society. It is also the only legal,
nonprescription drug that
produces euphoria.
fatty liver: an early stage of liver
deterioration seen in several
diseases, including kwashiorkor
and alcoholic liver disease.
Fatty liver is characterized by
an accumulation of fat in the
liver cells.
fibrosis (fye-BROH-sis): an
intermediate stage of liver
deterioration seen in several
diseases, including viral hepatitis
and alcoholic liver disease. In
fibrosis, the liver cells lose their
function and assume the
characteristics of connective
tissue cells (fibers).
MEOS or microsomal (my-krow-
SO-mal) ethanol-oxidizing
system: a system of enzymes in
the liver that oxidize not only
alcohol but also several classes
of drugs.
moderation: in relation to
alcohol consumption, not more
than two drinks a day for the
average-size man and not more
than one drink a day for the
average-size woman.
NAD (nicotinamide adenine
dinucleotide): the main
coenzyme form of the vitamin
niacin. Its reduced form is NADH.
narcotic (nar-KOT-ic): a drug
that dulls the senses, induces
sleep, and becomes addictive
with prolonged use.
proof: a way of stating the
percentage of alcohol in distilled
liquor. Liquor that is 100 proof
is 50% alcohol; 90 proof is 45%,
and so forth.
Wernicke-Korsakoff (VER-nee-key
KORE-sah-kof) syndrome: a
neurological disorder typically
associated with chronic
alcoholism and caused by a
deficiency of the B vitamin
thiamin; also called alcohol-
related dementia.
wine: an alcoholic beverage
made by fermenting grape
juice.
Wines contain 7 to 24 percent alcohol by volume; those contain-
ing 14 percent or more must state their alcohol content on the
label, whereas those with less than 14 percent may simply state
“table wine” or “light wine.” Beers typically contain less than 5
percent alcohol by volume and malt liquors, 5 to 8 percent; regu-
lations vary, with some states requiring beer labels to show the
alcohol content and others prohibiting such statements.
©
Polara
Studios,
Inc.
Matthew
Farruggio
drink per day for women. (Pregnant women are advised to abstain
from alcohol, as Highlight 14 explains.) Notice that this advice is

240 •
stated as a maximum, not as an average; seven drinks one night a
week would not be considered moderate, even though one a day
would be. Doubtless some people could consume slightly more;
others could not handle nearly so much without risk. The amount a
person can drink safely is highly individual, depending on genetics,
health, gender, body composition, age, and family history.
Alcohol in the Body
From the moment an alcoholic beverage enters the body, alcohol
is treated as if it has special privileges. Unlike foods, which require
time for digestion, alcohol needs no digestion and is quickly ab-
sorbed across the walls of an empty stomach, reaching the brain
within a few minutes. Consequently, a person can immediately feel
euphoric when drinking, especially on an empty stomach.
When the stomach is full of food, alcohol has less chance of
touching the walls and diffusing through, so its influence on the
brain is slightly delayed. This information leads to a practical tip: eat
snacks when drinking alcoholic beverages. Carbohydrate snacks
slow alcohol absorption and high-fat snacks slow peristalsis, keep-
ing the alcohol in the stomach longer. Salty snacks make a person
thirsty; to quench thirst, drink water instead of more alcohol.
The stomach begins to break down alcohol with its alcohol de-
hydrogenase enzyme. Women produce less of this stomach en-
zyme than men; consequently, more alcohol reaches the intestine
for absorption into the bloodstream. As a result, women absorb
more alcohol than men of the same size who drink the same
amount of alcohol. Consequently, they are more likely to become
more intoxicated on less alcohol than men. Such differences be-
tween men and women help explain why women have a lower al-
cohol tolerance and a lower recommendation for moderate intake.
In the small intestine, alcohol is rapidly absorbed. From this
point on, alcohol receives priority treatment: it gets absorbed and
metabolized before most nutrients. Alcohol’s priority status helps
to ensure a speedy disposal and reflects two facts: alcohol cannot
be stored in the body, and it is potentially toxic.
Alcohol Arrives in the Liver
The capillaries of the digestive tract merge into veins that carry
the alcohol-laden blood to the liver. These veins branch and re-
branch into capillaries that touch every liver cell. Liver cells are the
only other cells in the body that can make enough of the alcohol
dehydrogenase enzyme to oxidize alcohol at an appreciable rate.
The routing of blood through the liver cells gives them the
chance to dispose of some alcohol before it moves on.
Alcohol affects every organ of the body, but the most dramatic
evidence of its disruptive behavior appears in the liver. If liver cells
could talk, they would describe alcohol as demanding, egocen-
tric, and disruptive of the liver’s efficient way of running its busi-
ness. For example, liver cells normally prefer fatty acids as their
fuel, and they like to package excess fatty acids into triglycerides
and ship them out to other tissues. When alcohol is present, how-
ever, the liver cells are forced to metabolize alcohol and let the
fatty acids accumulate, sometimes in huge stockpiles. Alcohol
metabolism can also permanently change liver cell structure, im-
pairing the liver’s ability to metabolize fats. As a result, heavy
drinkers develop fatty livers.
The liver is the primary site of alcohol metabolism.4 It can
process about 1/2 ounce of ethanol per hour (the amount in a typ-
ical drink), depending on the person’s body size, previous drink-
ing experience, food intake, and general health. This maximum
rate of alcohol breakdown is set by the amount of alcohol dehy-
drogenase available. If more alcohol arrives at the liver than the
enzymes can handle, the extra alcohol travels to all parts of the
body, circulating again and again until liver enzymes are finally
available to process it. Another practical tip derives from this in-
formation: drink slowly enough to allow the liver to keep up—no
more than one drink per hour.
The amount of alcohol dehydrogenase enzyme present in the
liver varies with individuals, depending on the genes they have in-
herited and on how recently they have eaten. Fasting for as little
as a day forces the body to degrade its proteins, including the al-
cohol-processing enzymes, and this can slow the rate of alcohol
metabolism by half. Drinking after not eating all day thus causes
the drinker to feel the effects more promptly for two reasons: rapid
absorption and slowed breakdown. By maintaining higher blood
alcohol concentrations for longer times, alcohol can anesthetize
the brain more completely (as described later in this highlight).
The alcohol dehydrogenase enzyme breaks down alcohol by
removing hydrogens in two steps. (Figure H7-2 provides a simpli-
fied diagram of alcohol metabolism; Appendix C provides the
chemical details.) In the first step, alcohol dehydrogenase oxi-
dizes alcohol to acetaldehyde. High concentrations of acetalde-
hyde in the brain and other tissues are responsible for many of the
damaging effects of alcohol abuse.
Highlight 7
NADH + H+
NAD+ NADH + H+
NAD+
Acetate
Acetaldehyde
dehydrogenase
Alcohol
dehydrogenase
Acetaldehyde
Alcohol
(ethanol)
CoA
Acetyl CoA
The conversion of alcohol to acetyl CoA requires the B vitamin niacin in its role as the coenzyme NAD. When the
enzymes oxidize alcohol, they remove H atoms and attach them to NAD. Thus NAD is used up and NADH accumulates.
(Note: More accurately, NAD+ is converted to NADH + H+
.)
FIGURE H7-2 Alcohol Metabolism

In the second step, a related enzyme, acetaldehyde dehydro-
genase, converts acetaldehyde to acetate, which is then con-
verted to acetyl CoA—the “crossroads” compound introduced in
Chapter 7 that can enter the TCA cycle to generate energy. These
reactions produce hydrogen ions (H+). The B vitamin niacin, in its
role as the coenzyme NAD (nicotinamide adenine dinu-
cleotide), helpfully picks up these hydrogen ions (becoming
NADH). Thus, whenever the body breaks down alcohol, NAD di-
minishes and NADH accumulates. (Chapter 10 presents informa-
tion on NAD and the other coenzyme roles of the B vitamins.)
Alcohol Disrupts the Liver
During alcohol metabolism, the multitude of other metabolic
processes for which NAD is required, including glycolysis, the
TCA cycle, and the electron transport chain, falter. Its presence is
sorely missed in these energy pathways because it is the chief car-
rier of the hydrogens that travel with their electrons along the
electron transport chain. Without adequate NAD, these energy
pathways cannot function. Traffic either backs up, or an alternate
route is taken. Such changes in the normal flow of energy path-
ways have striking physical consequences.
For one, the accumulation of hydrogen ions during alcohol me-
tabolism shifts the body’s acid-base balance toward acid. For an-
other, the accumulation of NADH slows the TCA cycle, so pyruvate
and acetyl CoA build up. Excess acetyl CoA then takes the route to
fatty acid synthesis (as Figure H7-3 illustrates), and fat clogs the liver.
As you might expect, a liver overburdened with fat cannot
function properly. Liver cells become less efficient at performing a
number of tasks. Much of this inefficiency impairs a person’s nu-
tritional health in ways that cannot be corrected by diet alone.
For example, the liver has difficulty activating vitamin D, as well
as producing and releasing bile. To overcome such problems, a
person needs to stop drinking alcohol.
The synthesis of fatty acids accelerates with exposure to alco-
hol. Fat accumulation can be seen in the liver after a single night
of heavy drinking. Fatty liver, the first stage of liver deterioration
seen in heavy drinkers, interferes with the distribution of nutrients
and oxygen to the liver cells. Fatty liver is reversible with absti-
nence from alcohol. If fatty liver lasts long enough, however, the
liver cells will die and form fibrous scar tissue. This second stage
of liver deterioration is called fibrosis. Some liver cells can regen-
erate with good nutrition and abstinence from alcohol, but in the
most advanced stage, cirrhosis, damage is the least reversible.
The fatty liver has difficulty generating glucose from protein.
Without gluconeogenesis, blood glucose can plummet, leading
to irreversible damage to the central nervous system.
The lack of glucose together with the overabundance of acetyl
CoA sets the stage for ketosis. The body uses the acetyl CoA to
make ketone bodies; their acidity pushes the acid-base balance
further toward acid and suppresses nervous system activity.
Excess NADH also promotes the making of lactate from pyru-
vate. The conversion of pyruvate to lactate uses the hydrogens
from NADH and restores some NAD, but a lactate buildup has se-
rious consequences of its own—it adds still further to the body’s
acid burden and interferes with the excretion of another acid, uric
acid, causing inflammation of the joints.
Alcohol alters both amino acid and protein metabolism. Syn-
thesis of proteins important in the immune system slows down,
weakening the body’s defenses against infection. Protein defi-
ciency can develop, both from a diminished synthesis of protein
and from a poor diet. Normally, the cells would at least use the
amino acids from the protein foods a person eats, but the
drinker’s liver deaminates the amino acids and uses the carbon
fragments primarily to make fat or ketones. Eating well does not
protect the drinker from protein depletion; a person has to stop
drinking alcohol.
The liver’s priority treatment of alcohol affects its handling of
drugs as well as nutrients. In addition to the dehydrogenase enzyme
FIGURE H7-3 Alternate Route for Acetyl CoA: To Fat
NADH + H+
NAD+
NADH + H+
NAD+
Acetate
Acetaldehyde
dehydrogenase
Alcohol
dehydrogenase
Acetaldehyde
CoA
Alcohol
(ethanol)
Fat (triglycerides)
Fatty acids
TCA
Cycle
Acetyl CoA
Acetyl CoA molecules are blocked from getting into the TCA cycle by the high level of NADH. Instead of being used for
energy, the acetyl CoA molecules become building blocks for fatty acids.

242 • Highlight 7
FIGURE H7-4 Alcohol’s Effects on the Brain
Judgment and reasoning centers are most sensitive to
alcohol. When alcohol flows to the brain, it first sedates the
frontal lobe, the center of all conscious activity. As the
alcohol molecules diffuse into the cells of these lobes,
they interfere with reasoning and judgment.
Midbrain
Respiration and heart action are the last to be affected.
Finally, the conscious brain is completely subdued,
and the person passes out. Now the person can drink
no more; this is fortunate because higher doses would
anesthetize the deepest brain centers that control
breathing and heartbeat, causing death.
Speech and vision centers in the midbrain are
affected next. If the drinker drinks faster than the rate
at which the liver can oxidize the alcohol, blood
alcohol concentrations rise: the speech and vision
centers of the brain become sedated.
Voluntary muscular control is then affected. At still
higher concentrations, the cells in the cerebellum
responsible for coordination of voluntary muscles are
affected, including those used in speech, eye-hand
coordination, and limb movements. At this point people
under the influence stagger or weave when they try to
walk, or they may slur their speech.
1
2
Frontal lobe
1
Pons,
Medulla oblongata
4
Cerebellum
3
2
3
4
already described, the liver possesses an enzyme system that metab-
olizes both alcohol and several other types of drugs. Called the
MEOS (microsomal ethanol-oxidizing system), this system
handles about one-fifth of the total alcohol a person consumes. At
high blood concentrations or with repeated exposures, alcohol
stimulates the synthesis of enzymes in the MEOS. The result is a
more efficient metabolism of alcohol and tolerance to its effects.
As a person’s blood alcohol rises, alcohol competes with—and
wins out over—other drugs whose metabolism also relies on the
MEOS. If a person drinks and uses another drug at the same time,
the MEOS will dispose of alcohol first and metabolize the drug
more slowly. While the drug waits to be handled later, the dose
may build up so that its effects are greatly amplified—sometimes
to the point of being fatal.
In contrast, once a heavy drinker stops drinking and alcohol is
no longer competing with other drugs, the enhanced MEOS me-
tabolizes drugs much faster than before. As a result, determining
the correct dosages of medications can be challenging.
This discussion has emphasized the major way that the blood
is cleared of alcohol—metabolism by the liver—but there is an-
other way. About 10 percent of the alcohol leaves the body
through the breath and in the urine. This is the basis for the
breath and urine tests for drunkenness. The amounts of alcohol in
the breath and in the urine are in proportion to the amount still
in the bloodstream and brain. In nearly all states, legal drunken-
ness is set at 0.10 percent or less, reflecting the relationship be-
tween alcohol use and traffic and other accidents.
Alcohol Arrives in the Brain
Alcohol is a narcotic. People used it for centuries as an anesthetic
because it can deaden pain. But alcohol was a poor anesthetic be-
cause one could never be sure how much a person would need
and how much would be a fatal dose. Consequently, new, more
predictable anesthetics have replaced alcohol. Nonetheless, alco-
hol continues to be used today as a kind of social anesthetic to
help people relax or to relieve anxiety. People think that alcohol is
a stimulant because it seems to relieve inhibitions. Actually,
though, it accomplishes this by sedating inhibitory nerves, which
are more numerous than excitatory nerves. Ultimately, alcohol
acts as a depressant and affects all the nerve cells. Figure H7-4 de-
scribes alcohol’s effects on the brain.
It is lucky that the brain centers respond to a rising blood alco-
hol concentration in the order described in Figure H7-4 because a
person usually passes out before managing to drink a lethal dose.
It is possible, though, to drink so fast that the effects of alcohol
continue to accelerate after the person has passed out. Occasion-
ally, a person dies from drinking enough to stop the heart before
passing out. Table H7-1 shows the blood alcohol levels that corre-
spond to progressively greater intoxication, and Table H7-2 shows
the brain responses that occur at these blood levels.
Like liver cells, brain cells die with excessive exposure to alco-
hol. Liver cells may be replaced, but not all brain cells can regen-
erate. Thus some heavy drinkers suffer permanent brain damage.

Water loss is accompanied by the loss of important minerals.
As Chapters 12 and 13 explain, these minerals are vital to the
body’s fluid balance and to many chemical reactions in the cells,
including muscle action. Detoxification treatment includes
restoration of mineral balance as quickly as possible.
Alcohol and Malnutrition
For many moderate drinkers, alcohol does not suppress food intake
and may actually stimulate appetite. Moderate drinkers usually
consume alcohol as added energy—on top of their normal food
intake. In addition, alcohol in moderate doses is efficiently metab-
olized. Consequently, alcohol can contribute to body fat and
weight gain—either by inhibiting oxidation or by being con-
verted to fat.6 Metabolically, alcohol is almost as efficient as fat in
promoting obesity; each ounce of alcohol represents about a half-
ounce of fat. Alcohol’s contribution to body fat is most evident in
the central obesity that commonly accompanies alcohol con-
sumption, popularly—and appropriately—known as the “beer
belly.”7 Alcohol in heavy doses, though, is not efficiently metabo-
lized, generating more heat than fat. Heavy drinkers usually con-
sume alcohol as substituted energy—instead of their normal food
intake. They tend to eat poorly and suffer malnutrition.
Alcohol is rich in energy (7 kcalories per gram), but as with pure
sugar or fat, the kcalories are empty of nutrients. The more alcohol
people drink, the less likely that they will eat enough food to obtain
adequate nutrients. The more kcalories spent on alcohol, the fewer
kcalories available to spend on nutritious foods. Table H7-3 (p. 244)
shows the kcalorie amounts of typical alcoholic beverages.
Chronic alcohol abuse not only displaces nutrients from the diet,
but it also interferes with the body’s metabolism of nutrients. Most
dramatic is alcohol’s effect on the B vitamin folate. The liver loses its
ability to retain folate, and the kidneys increase their excretion of it.
Alcohol abuse creates a folate deficiency that devastates digestive
TABLE H7-1 Alcohol Doses and Approximate Blood Level Percentages for Men and Women
Drinksa Body Weight in Pounds—Men
100 120 140 160 180 200 220 240
00 00 00 00 00 00 00 00
1 .04 .03 .03 .02 .02 .02 .02 .02
2 .08 .06 .05 .05 .04 .04 .03 .03
3 .11 .09 .08 .07 .06 .06 .05 .05
4 .15 .12 .11 .09 .08 .08 .07 .06
5 .19 .16 .13 .12 .11 .09 .09 .08
6 .23 .19 .16 .14 .13 .11 .10 .09
7 .26 .22 .19 .16 .15 .13 .12 .11
8 .30 .25 .21 .19 .17 .15 .14 .13
9 .34 .28 .24 .21 .19 .17 .15 .14
10 .38 .31 .27 .23 .21 .19 .17 .16
TABLE H7-2 Alcohol Blood Levels and Brain Responses
Blood Alcohol
Concentration Effect on Brain
0.05 Impaired judgment, relaxed inhibitions, altered
mood, increased heart rate
0.10 Impaired coordination, delayed reaction time,
exaggerated emotions, impaired peripheral vision,
impaired ability to operate a vehicle
0.15 Slurred speech, blurred vision, staggered walk,
seriously impaired coordination and judgment
0.20 Double vision, inability to walk
0.30 Uninhibited behavior, stupor, confusion, inability to
comprehend
0.40 to 0.60 Unconsciousness, shock, coma, death (cardiac or
respiratory failure)
NOTE: Blood alcohol concentration depends on a number of factors, including alcohol in the
beverage, the rate of consumption, the person’s gender, and body weight. For example, a 100-
pound female can become legally drunk (0.10 concentration) by drinking three beers in an
hour, whereas a 220-pound male consuming that amount at the same rate would have a 0.05
blood alcohol concentration.
Whether alcohol impairs cognition in moderate drinkers is
unclear.5
People who drink alcoholic beverages may notice that they
urinate more, but they may be unaware of the vicious cycle that
results. Alcohol depresses production of antidiuretic hormone
(ADH), a hormone produced by the pituitary gland that retains
water—consequently, with less ADH, more water is lost. Loss of
body water leads to thirst, and thirst leads to more drinking. Wa-
ter will relieve dehydration, but the thirsty drinker may drink alco-
hol instead, which only worsens the problem. Such information
provides another practical tip: drink water when thirsty and be-
fore each alcoholic drink. Drink an extra glass or two before go-
ing to bed. This strategy will help lessen the effects of a hangover.
IMPAIRMENT
BEGINS
DRIVING SKILLS
SIGNIFICANTLY
AFFECTED
LEGALLY
INTOXICATED
Drinksa Body Weight in Pounds—Women
90 100 120 140 160 180 200 220 240
00 00 00 00 00 00 00 00 00
1 .05 .05 .04 .03 .03 .03 .02 .02 .02
2 .10 .09 .08 .07 .06 .05 .05 .04 .04
3 .15 .14 .11 .10 .09 .08 .07 .06 .06
4 .20 .18 .15 .13 .11 .10 .09 .08 .08
5 .25 .23 .19 .16 .14 .13 .11 .10 .09
6 .30 .27 .23 .19 .17 .15 .14 .12 .11
7 .35 .32 .27 .23 .20 .18 .16 .14 .13
8 .40 .36 .30 .26 .23 .20 .18 .17 .15
9 .45 .41 .34 .29 .26 .23 .20 .19 .17
10 .51 .45 .38 .32 .28 .25 .23 .21 .19
DRIVING SKILLS
SIGNIFICANTLY
AFFECTED
LEGALLY
INTOXICATED
NOTE: In some states, driving under the influence is proved when an adult’s blood contains 0.08 percent alcohol, and in others, 0.10. Many states have adopted a “zero-tolerance” policy for drivers
under age 21, using 0.02 percent as the limit.
aTaken within an hour or so; each drink equivalent to 1
⁄2 ounce pure ethanol.
SOURCE: National Clearinghouse for Alcohol and Drug Information
ONLY SAFE
DRIVING LIMIT
ONLY SAFE
DRIVING LIMIT
IMPAIRMENT
BEGINS

244 • Highlight 7
system function. The intestine normally releases and retrieves fo-
late continuously, but it becomes damaged by folate deficiency
and alcohol toxicity, so it fails to retrieve its own folate and misses
any that may trickle in from food as well. Alcohol also interferes
with the action of folate in converting the amino acid homocys-
teine to methionine. The result is an excess of homocysteine,
which has been linked to heart disease, and an inadequate supply
of methionine, which slows the production of new cells, espe-
cially the rapidly dividing cells of the intestine and the blood. The
combination of poor folate status and alcohol consumption has
also been implicated in promoting colorectal cancer.
The inadequate food intake and impaired nutrient absorption
that accompany chronic alcohol abuse frequently lead to a defi-
ciency of another B vitamin—thiamin. In fact, the cluster of thi-
amin-deficiency symptoms commonly seen in chronic alcoholism
has its own name—the Wernicke-Korsakoff syndrome. This
syndrome is characterized by paralysis of the eye muscles, poor
muscle coordination, impaired memory, and damaged nerves; it
and other alcohol-related memory problems may respond to thi-
amin supplements.
Acetaldehyde, an intermediate in alcohol metabolism (review
Figure H7-2, p. 240), interferes with nutrient use, too. For exam-
ple, acetaldehyde dislodges vitamin B6 from its protective binding
protein so that it is destroyed, causing a vitamin B6 deficiency
and, thereby, lowered production of red blood cells.
Malnutrition occurs not only because of lack of intake and al-
tered metabolism but because of direct toxic effects as well. Alco-
hol causes stomach cells to oversecrete both gastric acid and
histamine, an immune system agent that produces inflammation.
Beer in particular stimulates gastric acid secretion, irritating the
linings of the stomach and esophagus and making them vulnera-
ble to ulcer formation.
Overall, nutrient deficiencies are virtually inevitable in alcohol
abuse, not only because alcohol displaces food but also because al-
cohol directly interferes with the body’s use of nutrients, making
them ineffective even if they are present. Intestinal cells fail to ab-
sorb B vitamins, notably, thiamin, folate, and vitamin B12. Liver cells
lose efficiency in activating vitamin D. Cells in the retina of the eye,
which normally process the alcohol form of vitamin A (retinol) to its
aldehyde form needed in vision (retinal), find themselves process-
ing ethanol to acetaldehyde instead. Likewise, the liver cannot con-
vert the aldehyde form of vitamin A to its acid form (retinoic acid),
which is needed to support the growth of its (and all) cells.
Regardless of dietary intake, excessive drinking over a lifetime
creates deficits of all the nutrients mentioned in this discussion
and more. No diet can compensate for the damage caused by
heavy alcohol consumption.
Alcohol’s Short-Term Effects
The effects of abusing alcohol may be apparent immediately, or
they may not become evident for years to come. Among the im-
mediate consequences, all of the following involve alcohol use:8
• One-quarter of all emergency-room admissions
• One-third of all suicides
• One-half of all homicides
• One-half of all domestic violence incidents
• One-half of all traffic fatalities
• One-half of all fire victim fatalities
These statistics are sobering. The consequences of heavy
drinking touch all races and all segments of society—men and
women, young and old, rich and poor. One group particularly
hard hit by heavy drinking is college students—not because they
are prone to alcoholism, but because they live in an environment
and are in a developmental stage of life in which heavy drinking
is considered acceptable.9
Heavy drinking or binge drinking (defined as at least four
drinks in a row for women and five drinks in a row for men) is
widespread on college campuses and poses serious health and so-
cial consequences to drinkers and nondrinkers alike.*10 In fact,
binge drinking can kill: the respiratory center of the brain be-
comes anesthetized, and breathing stops. Acute alcohol intoxica-
tion can cause coronary artery spasms, leading to heart attacks.
Binge drinking is especially common among college students
who live in a fraternity or sorority house, attend parties fre-
quently, engage in other risky behaviors, and have a history of
binge drinking in high school. Compared with nondrinkers or
moderate drinkers, people who frequently binge drink (at least
three times within two weeks) are more likely to engage in unpro-
* This definition of binge drinking, without specification of time elapsed, is
consistent with standard practice in alcohol research.
TABLE H7-3 kCalories in Alcoholic Beverages and Mixers
Amount Energy
Beverage (oz) (kcal)
Beer
Regular 12 150
Light 12 78–131
Nonalcoholic 12 32–82
Distilled liquor (gin, rum, vodka, whiskey)
80 proof 11
⁄2 100
86 proof 11
⁄2 105
90 proof 11
⁄2 110
Liqueurs
Coffee liqueur, 53 proof 11
⁄2 175
Coffee and cream liqueur, 34 proof 11
⁄2 155
Crème de menthe, 72 proof 11
⁄2 185
Mixers
Club soda 12 0
Cola 12 150
Cranberry juice cocktail 8 145
Diet drinks 12 2
Ginger ale or tonic 12 125
Grapefruit juice 8 95
Orange juice 8 110
Tomato or vegetable juice 8 45
Wine
Dessert 31
⁄2 110–135
Nonalcoholic 8 14
Red or rosé 31
⁄2 75
White 31
⁄2 70
Wine cooler 12 170

tected sex, have multiple sex partners, damage property, and as-
sault others.11 On average, every day alcohol is involved in the:12
• Death of 5 college students
• Sexual assault of 266 college students
• Injury of 1641 college students
• Assault of 1907 college students
Binge drinkers skew the statistics on college students’ alcohol
use. The median number of drinks consumed by college students
is 1.5 per week, but for binge drinkers, it is 14.5. Nationally, only
20 percent of all students are frequent binge drinkers; yet they ac-
count for two-thirds of all the alcohol students report consuming
and most of the alcohol-related problems.
Binge drinking is not limited to college campuses, of course,
but it is most common among 18- to 24-year-olds.13 That age
group and environment seem most accepting of such behavior
despite its problems. Social acceptance may make it difficult for
binge drinkers to recognize themselves as problem drinkers. For
this reason, interventions must focus both on educating individu-
als and on changing the campus social environment.14 The dam-
age alcohol causes only becomes worse if the pattern is not
broken. Alcohol abuse sets in much more quickly in young people
than in adults. Those who start drinking at an early age more of-
ten suffer from alcoholism than people who start later on. Table
H7-4 lists the key signs of alcoholism.
Alcohol’s Long-Term Effects
The most devastating long-term effect of alcohol is the damage
done to a child whose mother abused alcohol during pregnancy.
The effects of alcohol on the unborn and the message that pregnant
women should not drink alcohol are presented in Highlight 14.
For nonpregnant adults, a drink or two sets in motion many de-
structive processes in the body, but the next day’s abstinence reverses
them. As long as the doses are moderate, the time between them is
ample, and nutrition is adequate, recovery is probably complete.
If the doses of alcohol are heavy and the time between them
short, complete recovery cannot take place. Repeated onslaughts
of alcohol gradually take a toll on all parts of the body (see Table
H7-5, p. 246). Compared with nondrinkers and moderate
drinkers, heavy drinkers have significantly greater risks of dying
from all causes.15 Excessive alcohol consumption is the third lead-
ing preventable cause of death in the United States.16
Personal Strategies
One obvious option available to people attending social gather-
ings is to enjoy the conversation, eat the food, and drink nonalco-
holic beverages. Several nonalcoholic beverages are available that
mimic the look and taste of their alcoholic counterparts. For those
who enjoy champagne or beer, sparkling ciders and beers without
alcohol are available. Instead of drinking a cocktail, a person can
sip tomato juice with a slice of lime and a stalk of celery or just a
plain cola beverage. Any of these drinks can ease conversation.
The person who chooses to drink alcohol should sip each drink
slowly with food. The alcohol should arrive at the liver cells slowly
enough that the enzymes can handle the load. It is best to space
drinks, too, allowing about an hour or so to metabolize each drink.
If you want to help sober up a friend who has had too much to
drink, don’t bother walking arm in arm around the block. Walking
muscles have to work harder, but muscle cells can’t metabolize al-
cohol; only liver cells can. Remember that each person has a lim-
ited amount of the alcohol dehydrogenase enzyme that clears the
blood at a steady rate. Time alone will do the job.
Nor will it help to give your friend a cup of coffee. Caffeine is a
stimulant, but it won’t speed up alcohol metabolism. The police
say ruefully, “If you give a drunk a cup of coffee, you’ll just have a
wide-awake drunk on your hands.” Table H7-6 (p. 246) presents
other alcohol myths.
People who have passed out from drinking need 24 hours to
sober up completely. Let them sleep, but watch over them. En-
courage them to lie on their sides, instead of their backs. That
way, if they vomit, they won’t choke.
Don’t drive too soon after drinking. The lack of glucose for the
brain’s function and the length of time needed to clear the blood
of alcohol make alcohol’s adverse effects linger long after its
blood concentration has fallen. Driving coordination is still im-
paired the morning after a night of drinking, even if the drinking
was moderate. Responsible aircraft pilots know that they must al-
low 24 hours for their bodies to clear alcohol completely, and
they refuse to fly any sooner. The Federal Aviation Administration
and major airlines enforce this rule.
TABLE H7-4 Signs of Alcoholism
• Tolerance—the person needs higher and higher intakes of alcohol to achieve intoxication
• Withdrawal—the person who stops drinking experiences anxiety, agitation, increased blood pressure, or seizures, or seeks alcohol to relieve these symptoms
• Impaired control—the person intends to have 1 or 2 drinks, but has 9 or 10 instead, or the person tries to control or quit drinking, but fails
• Disinterest—the person neglects important social, family, job, or school activities because of drinking
• Time—the person spends a great deal of time obtaining and drinking alcohol or recovering from excessive drinking
• Impaired ability—the person’s intoxication or withdrawal symptoms interfere with work, school, or home
• Problems—the person continues drinking despite physical hazards or medical, legal, psychological, family, employment, or school problems
The presence of three or more of these conditions is required to make a diagnosis.
SOURCE: Adapted from Diagnostic and Statistical Manual of Mental Disorders, 4th ed. (Washington, D.C.: American Psychiatric Association, 1994).

246 • Highlight 7
TABLE H7-6 Myths and Truths Concerning Alcohol
Myth: Hard liquors such as rum, vodka, and tequila are more harmful than wine and beer.
Truth: The damage caused by alcohol depends largely on the amount consumed. Compared with hard liquor, beer and wine have relatively low percentages
of alcohol, but they are often consumed in larger quantities.
Myth: Consuming alcohol with raw seafood diminishes the likelihood of getting hepatitis.
Truth: People have eaten contaminated oysters while drinking alcoholic beverages and not gotten as sick as those who were not drinking. But do not be
misled: hepatitis is too serious an illness for anyone to depend on alcohol for protection.
Myth: Alcohol stimulates the appetite.
Truth: For some people, alcohol may stimulate appetite, but it seems to have the opposite effect in heavy drinkers. Heavy drinkers tend to eat poorly and
suffer malnutrition.
Myth: Drinking alcohol is healthy.
Truth: Moderate alcohol consumption is associated with a lower risk for heart disease (see Chapter 27 for more details). Higher intakes, however, raise the
risks for high blood pressure, stroke, heart disease, some cancers, accidents, violence, suicide, birth defects, and deaths in general. Furthermore,
excessive alcohol consumption damages the liver, pancreas, brain, and heart. No authority recommends that nondrinkers begin drinking alcoholic
beverages to obtain health benefits.
Myth: Wine increases the body’s absorption of minerals.
Truth: Wine may increase the body’s absorption of potassium, calcium, phosphorus, magnesium, and zinc, but the alcohol in wine also promotes the body’s
excretion of these minerals, so no benefit is gained.
Myth: Alcohol is legal and, therefore, not a drug.
Truth: Alcohol is legal for adults 21 years old and older, but it is also a drug—a substance that alters one or more of the body’s functions.
Myth: A shot of alcohol warms you up.
Truth: Alcohol diverts blood flow to the skin making you feel warmer, but it actually cools the body.
Myth: Wine and beer are mild; they do not lead to alcoholism.
Truth: Alcoholism is not related to the kind of beverage, but rather to the quantity and frequency of consumption.
Myth: Mixing different types of drinks gives you a hangover.
Truth: Too much alcohol in any form produces a hangover.
Myth: Alcohol is a stimulant.
Truth: People think alcohol is a stimulant because it seems to relieve inhibitions, but it does so by depressing the activity of the brain. Alcohol is medically
defined as a depressant drug.
Myth: Beer is a great source of carbohydrate, vitamins, minerals, and fluids.
Truth: Beer does provide some carbohydrate, but most of its kcalories come from alcohol. The few vitamins and minerals in beer cannot compete with rich
food sources. And the diuretic effect of alcohol causes the body to lose more fluid in urine than is provided by the beer.
TABLE H7-5 Health Effects of Heavy Alcohol Consumption
Health Problem Effects of Alcohol
Arthritis Increases the risk of inflamed joints
Cancer Increases the risk of cancer of the liver, pancreas, rectum, and breast; increases the risk of cancer of the lungs, mouth, pharynx,
larynx, and esophagus, where alcohol interacts synergistically with tobacco
Fetal alcohol syndrome Causes physical and behavioral abnormalities in the fetus (see Highlight 14)
Heart disease In heavy drinkers, raises blood pressure, blood lipids, and the risk of stroke and heart disease; when compared with those who
abstain, heart disease risk is generally lower in light-to-moderate drinkers (see Chapter 27)
Hyperglycemia Raises blood glucose
Hypoglycemia Lowers blood glucose, especially in people with diabetes
Infertility Increases the risks of menstrual disorders and spontaneous abortions (in women); suppresses luteinizing hormone (in women) and
testosterone (in men)
Kidney disease Enlarges the kidneys, alters hormone functions, and increases the risk of kidney failure
Liver disease Causes fatty liver, alcoholic hepatitis, and cirrhosis
Malnutrition Increases the risk of protein-energy malnutrition; low intakes of protein, calcium, iron, vitamin A, vitamin C, thiamin, vitamin B6,
and riboflavin; and impaired absorption of calcium, phosphorus, vitamin D, and zinc
Nervous disorders Causes neuropathy and dementia; impairs balance and memory
Obesity Increases energy intake, but is not a primary cause of obesity
Psychological disturbances Causes depression, anxiety, and insomnia
NOTE: This list is by no means all-inclusive. Alcohol has direct toxic effects on all body systems.

Look again at the drawing of the brain in Figure H7-4, and
note that when someone drinks, judgment fails first. Judgment
might tell a person to limit alcohol consumption to two drinks at
a party, but if the first drink takes judgment away, many more
drinks may follow. The failure to stop drinking as planned, on re-
peated occasions, is a danger sign warning that the person
should not drink at all. The accompanying Nutrition on the Net
provides websites for organizations that offer information about
alcohol and alcohol abuse.
Ethanol interferes with a multitude of chemical and hor-
monal reactions in the body—many more than have been enu-
merated here. With heavy alcohol consumption, the potential
for harm is great. The best way to escape the harmful effects of
alcohol is, of course, to refuse alcohol altogether. If you do drink
alcoholic beverages, do so with care, and in moderation.
• Search for “alcohol” at the U.S. Government health site:
www.healthfinder.gov
• Gather information on alcohol and drug abuse from the
National Clearinghouse for Alcohol and Drug Information
(NCADI): ncadi.samhsa.gov
• Learn more about alcoholism and drug dependence from
the National Council on Alcoholism and Drug Depen-
dence (NCADD): www.ncadd.org
• Visit the National Institute on Alcohol Abuse and Alco-
holism: www.collegedrinkingprevention.gov
• Find help for a family alcohol problem from Alateen and
Al-Anon Family support groups:
www.al-anon.alateen.org
• Find help for an alcohol or drug problem from Alcoholics
Anonymous (AA) or Narcotics Anonymous: www.aa.org
or www.wsoinc.com
• Search for “party” to find tips for hosting a safe party from
Mothers Against Drunk Driving (MADD): www.madd.org
1. D. J. Meyerhoff and coauthors, Health risks
of chronic moderate and heavy alcohol
consumption: How much is too much?
Alcoholism, Clinical and Experimental Research
29 (2005): 1334–1340; J. B. Standridge, R. G.
Zylstra, and S. M. Adams, Alcohol consump-
tion: An overview of benefits and risks,
Southern Medical Journal 97 (2004): 664–672.
2. V. Arndt and coauthors, Age, alcohol con-
sumption, and all-cause mortality, Annals of
Epidemiology 14 (2004): 750–753.
3. J. Connor and coauthors, The burden of
death, disease, and disability due to alcohol
in New Zealand, New Zealand Medical Journal
118 (2005): U1412.
4. L. E. Nagy, Molecular aspects of alcohol
metabolism: Transcription factors involved
in early ethanol-induced liver injury, Annual
Review of Nutrition 24 (2004): 55–78.
5. D. Krahn and coauthors, Alcohol use and
cognition at mid-life: The importance of
adjusting for baseline cognitive ability and
educational attainment, Alcoholism: Clinical
and Experimental Research 27 (2003):
1162–1166.
6. R. A. Breslow and B. A. Smothers, Drinking
patterns and body mass index in never
smokers: National Health Interview Survey,
1997–2001, American Journal of Epidemiology
161 (2005): 368–376; M. R. Yeomans, Effects
of alcohol on food and energy intake in
human subjects: Evidence for passive and
active over-consumption of energy, British
Journal of Nutrition 92 (2004): S31–S34; S. G.
Wannamethee and A. G. Shaper, Alcohol,
body weight, and weight gain in middle-
aged men, American Journal of Clinical Nutri-
tion 77 (2003): 1312–1317; E. Jequier,
Pathways to obesity, International Journal of
Obesity and Related Metabolic Disorders 26
(2002): S12–S17.
7. S. G. Wannamethee, A. G. Shaper, and P. H.
Whincup, Alcohol and adiposity: Effects of
quantity and type of drink and time relation
with meals, International Journal of Obesity
and Related Metabolic Disorders 29 (2005):
1436–1444; J. M. Dorn and coauthors,
Alcohol drinking patterns differentially
affect central adiposity as measured by
abdominal height in women and men,
Journal of Nutrition 133 (2003): 2655–2662.
8. Position paper on drug policy: Physician
Leadership on National Drug Policy
(PLNDP), Brown University Center for
Alcohol and Addiction Studies, 2000.
9. A. M. Brower, Are college students alco-
holics? Journal of American College Health 50
(2002): 253–255.
10. R. D. Brewer and M. H. Swahn, Binge drink-
ing and violence, Journal of the American
Medical Association 294 (2005): 616–618; H.
Wechsler and coauthors, Trends in college
binge drinking during a period of increased
prevention efforts—Findings from Harvard
School of Public Health College Alcohol
Study Surveys: 1993–2001, Journal of Ameri-
can College Health 50 (2002): 203–217.
11. Wechsler and coauthors, 2002.
12. R. W. Hingson and coauthors, Magnitude of
alcohol-related mortality and morbidity
among U.S. college students ages 18–24:
Changes from 1998 to 2001, Annual Review
of Public Health 26 (2005): 259–279.
13. National Center for Health Statistics, Chart-
book on Trends in the Health of Americans,
Alcohol consumption by adults 18 years of
age and over, according to selected charac-
teristics: United States, selected years
1997–2003, (2005): 264–266.
14. A. Ziemelis, R. B. Bucknam, and A. M.
Elfessi, Prevention efforts underlying de-
creases in binge drinking at institutions of
higher learning, Journal of American College
Health 50 (2002): 238–252.
15. A. Y. Strandberg and coauthors, Alcohol
consumption, 29-y total mortality, and
quality of life in men in old age, American
1366–1371; I. R. White, D. R. Altmann, and
K. Nanchahal, Alcohol consumption and
mortality: Modeling risks for men and
women at different ages, British Medical
Journal 325 (2002): 191–197.
16. Centers for Disease Control, Alcohol-attrib-
utable deaths and years of potential life
lost—United States, 2001, Morbidity and
Mortality Weekly Report 53 (2004): 866–870.
REFERENCES

It’s a simple mathematical equation: energy in + energy out = energy balance.
The reality, of course, is much more complex. One day you may devour a
dozen doughnuts at midnight and sleep through your morning workout—
tipping the scales toward weight gain. Another day you may snack on veggies
and train for this weekend’s 10K race—shifting the balance toward weight loss.
Your body weight—especially as it relates to your body fat—and your level of
fitness have consequences for your health. So, how are you doing? Are you
ready to see how your “energy in” and “energy out” balance and whether
your body weight and fat measures are consistent with good health?
The CengageNOW logo
Rosemary Weller/Getty Images

The body’s remarkable machinery can cope with many extremes of diet.
As Chapter 7 explained, both excess carbohydrate (glucose) and excess
protein (amino acids) can contribute to body fat. To some extent, amino
acids can be used to make glucose. To a very limited extent, even fat (the
glycerol portion) can be used to make glucose. But a grossly unbalanced
diet imposes hardships on the body. If energy intake is too low or if too lit-
tle carbohydrate or protein is supplied, the body must degrade its own lean
tissue to meet its glucose and protein needs. If energy intake is too high, the
body stores fat.
Both excessive and deficient body fat result from an energy imbalance.
The simple picture is as follows. People who have consumed more food en-
ergy than they have expended bank the surplus as body fat. To reduce
body fat, they need to expend more energy than they take in from food. In
contrast, people who have consumed too little food energy to support their
bodies’ activities have relied on their bodies’ fat stores and possibly some of
their lean tissues as well. To gain weight, these people need to take in more
food energy than they expend. As you will see, though, the details of the
body’s weight regulation are quite complex.1 This chapter describes energy
balance and body composition and examines the health problems associ-
ated with having too much or too little body fat. The next chapter presents
strategies toward resolving these problems.
Energy Balance
People expend energy continuously and eat periodically to refuel. Ideally, their en-
ergy intakes cover their energy expenditures without too much excess. Excess energy
is stored as fat, and stored fat is used for energy between meals. The amount of body
fat a person deposits in, or withdraws from, “storage” on any given day depends on
the energy balance for that day—the amount consumed (energy in) versus the
amount expended (energy out). When a person is maintaining weight, energy in
equals energy out. When the balance shifts, weight changes. For each 3500 kcalo-
ries eaten in excess, a pound of body fat is stored; similarly, a pound of fat is lost for
249
CHAPTER OUTLINE
Energy Balance
Energy In: The kCalories Foods
Provide • Food Composition • Food
Intake
Energy Out: The kCalories the Body
Expends • Components of Energy
Expenditure • Estimating Energy
Requirements
Body Weight, Body Composition,
and Health • Defining Healthy Body
Weight • Body Fat and Its Distribution •
Health Risks Associated with Body
Weight and Body Fat
HIGHLIGHT 8 Eating Disorders
8
Energy Balance
and Body
Composition
C H A P T E R
IN OUT
ENERGY
When energy in balances with energy out, a
person’s body weight is stable.

250 • CHAPTER 8
each 3500 kcalories expended beyond those consumed. ◆ The fat stores of even a
healthy-weight adult represent an ample reserve of energy—50,000 to 200,000
kcalories.
To maintain body weight in a healthy range, balance kcalories from foods
and beverages with kcalories expended.
Quick changes in body weight are not simple changes in fat stores. Weight
gained or lost rapidly includes some fat, large amounts of fluid, and some lean tis-
sues such as muscle proteins and bone minerals. (Because water constitutes about
60 percent of an adult’s body weight, retention or loss of water can greatly influence
body weight.) Even over the long term, the composition of weight gained or lost is
normally about 75 percent fat and 25 percent lean. During starvation, losses of fat
and lean are about equal. (Recall from Chapter 7 that without adequate carbohy-
drate, protein-rich lean tissues break down to provide glucose.) Invariably, though,
fat gains and losses are gradual. The next two sections examine the two sides of the
energy-balance equation: energy in and energy out.
When the energy consumed equals the energy expended, a person is in energy
balance and body weight is stable. If more energy is taken in than is ex-
pended, a person gains weight. If more energy is expended than is taken in, a
person loses weight.
IN SUMMARY
Energy In: The kCalories Foods
Provide
Foods and beverages provide the “energy in” part of the energy-balance equation.
How much energy a person receives depends on the composition of the foods and
beverages and on the amount the person eats and drinks.
Food Composition
To find out how many kcalories a food provides, a scientist can burn the food in a
bomb calorimeter (see Figure 8-1). When the food burns, energy is released in the
form of heat. The amount of heat given off provides a direct measure of the food’s en-
ergy value (remember that kcalories are units of heat energy). In addition to releas-
ing heat, these reactions generate carbon dioxide and water—just as the body’s cells
do when they metabolize the energy-yielding nutrients. When the food burns and
the chemical bonds break, the carbons (C) and hydrogens (H) combine with oxygens
(O) to form carbon dioxide (CO2) and water (H2O). The amount of oxygen con-
sumed gives an indirect measure ◆ of the amount of energy released.
A bomb calorimeter measures the available energy in foods but overstates the
amount of energy that the human body ◆ derives from foods. The body is less effi-
cient than a calorimeter and cannot metabolize all of the energy-yielding nutrients
in a food completely. Researchers can correct for this discrepancy mathematically
to create useful tables of the energy values of foods (such as Appendix H). These
Thermometer measures
temperature changes
Insulated
container
keeps
heat from
escaping
Food is
burned
Water in which temperature
increase from burning food
is measured
Heating
element
Reaction
chamber
(bomb)
Motorized
stirrer
FIGURE 8-1 Bomb Calorimeter
When food is burned, energy is released
in the form of heat. Heat energy is mea-
sured in kcalories.
◆ Food energy values can be determined by:
• Direct calorimetry, which measures
the amount of heat released
• Indirect calorimetry, which measures
the amount of oxygen consumed
◆ The number of kcalories that the body
derives from a food, in contrast to the
number of kcalories determined by
calorimetry, is the physiological fuel
value.
bomb calorimeter (KAL-oh-RIM-eh-ter): an
instrument that measures the heat energy
released when foods are burned, thus provid-
ing an estimate of the potential energy of the
foods.
• calor = heat
• metron = measure
◆ 1 lb body fat 3500 kcal
Body fat, or adipose tissue, is composed of
a mixture of mostly fat, some protein, and
water. A pound of body fat (454 g) is
approximately 87% fat, or (454 0.87) 395
g, and 395 g 9 kcal/g 3555 kcal.

ENERGY BALANCE AND BODY COMPOSITION • 251
values provide reasonable estimates, but they do not reflect the precise amount of
energy a person will derive from the foods consumed.
The energy values of foods can also be computed from the amounts of carbohy-
drate, fat, and protein (and alcohol, if present) in the foods.* For example, a food
◆ containing 12 grams of carbohydrate, 5 grams of fat, and 8 grams of protein will
provide 48 carbohydrate kcalories, 45 fat kcalories, and 32 protein kcalories, for a
total of 125 kcalories. (To review how to calculate the energy available from foods,
turn to p. 9.)
Food Intake
To achieve energy balance, the body must meet its needs without taking in too
much or too little energy. Somehow the body decides how much and how often to
eat—when to start eating and when to stop. As you will see, many signals initiate or
delay eating. Appetite refers to the sensations of hunger, satiation, and satiety that
prompt a person to eat or not eat.2
Hunger People eat for a variety of reasons, most obviously (although not necessar-
ily most commonly) because they are hungry. Most people recognize hunger as an
irritating feeling that prompts thoughts of food and motivates them to start eating.
In the body, hunger is the physiological response to a need for food triggered by
chemical messengers originating and acting in the brain, primarily in the hypo-
thalamus.3 Hunger can be influenced by the presence or absence of nutrients in
the bloodstream, the size and composition of the preceding meal, customary eating
patterns, climate (heat reduces food intake; cold increases it), exercise, hormones,
and physical and mental illnesses. Hunger determines what to eat, when to eat, and
how much to eat.
The stomach is ideally designed to handle periodic batches of food, and people
typically eat meals at roughly four-hour intervals. Four hours after a meal, most, if
not all, of the food has left the stomach. Most people do not feel like eating again
until the stomach is either empty or almost so. Even then, a person may not feel
hungry for quite a while.
Satiation During the course of a meal, as food enters the GI tract and hunger di-
minishes, satiation develops. As receptors in the stomach stretch and hormones
such as cholecystokinin increase, the person begins to feel full.4 The response: satia-
tion occurs and the person stops eating.
Satiety After a meal, the feeling of satiety continues to suppress hunger and al-
lows a person to not eat again for a while. Whereas satiation tells us to “stop eating,”
satiety reminds us to “not start eating again.” Figure 8-2 (p. 252) summarizes the re-
lationships among hunger, satiation, and satiety. Of course, people can override
these signals, especially when presented with stressful situations or favorite foods.
Overriding Hunger and Satiety Not surprisingly, eating can be triggered by
signals other than hunger, even when the body does not need food. Some people ex-
perience food cravings when they are bored or anxious. In fact, they may eat in re-
sponse to any kind of stress, ◆ negative or positive. (“What do I do when I’m
grieving? Eat. What do I do when I’m celebrating? Eat!”) Many people respond to
external cues such as the time of day (“It’s time to eat”) or the availability, sight, and
taste of food (“I’d love a piece of chocolate even though I’m stuffed”). Environmen-
tal influences such as large portion sizes, favorite foods, or an abundance or variety
of foods stimulate eating and increase energy intake.5 These cognitive influences ◆
can easily lead to weight gain.
Eating can also be suppressed by signals other than satiety, even when a person
is hungry. People with the eating disorder anorexia nervosa, for example, use
* Some of the food energy values in the table of food composition in Appendix H were derived by
bomb calorimetry, and many were calculated from their energy-yielding nutrient contents.
◆ Reminder:
• 1 g carbohydrate = 4 kcal
• 1 g fat = 9 kcal
• 1 g protein = 4 kcal
• 1 g alcohol = 7 kcal
As Chapter 1 mentioned, many scientists
measure food energy in kilojoules instead.
Conversion factors for these and other
measures are in the Aids to Calculation sec-
tion on the last two pages of the book.
◆ Eating in response to arousal is called
stress eating.
◆ Cognitive influences include perceptions,
memories, intellect, and social interactions.
appetite: the integrated response to the
sight, smell, thought, or taste of food that
initiates or delays eating.
hunger: the painful sensation caused by
a lack of food that initiates food-seeking
behavior.
hypothalamus (high-po-THAL-ah-mus): a
brain center that controls activities such as
maintenance of water balance, regulation of
body temperature, and control of appetite.
satiation (say-she-AY-shun): the feeling of
satisfaction and fullness that occurs during a
meal and halts eating. Satiation determines
how much food is consumed during a meal.
satiety: the feeling of fullness and satisfaction
that occurs after a meal and inhibits eating
until the next meal. Satiety determines how
much time passes between meals.

252 • CHAPTER 8
tremendous discipline to ignore the pangs of hunger. Some people simply cannot
eat during times of stress, negative or positive. (“I’m too sad to eat.” “I’m too ex-
cited to eat!”) Why some people overeat in response to stress and others cannot eat
at all remains a bit of a mystery, although researchers are beginning to understand
the connections between stress hormones, brain activity, and “comfort foods.”6 Fac-
tors that appear to be involved include how the person perceives the stress and
whether usual eating behaviors are restrained. (Highlight 8 features anorexia ner-
vosa and other eating disorders.)
Sustaining Satiation and Satiety The extent to which foods produce satiation and
sustain satiety depends in part on the nutrient composition of a meal.7 Of the three
energy-yielding nutrients, protein is considered the most satiating. Foods low in en-
ergy density are also more satiating.8 High-fiber foods effectively provide satiation by
filling the stomach and delaying the absorption of nutrients. For this reason, eating
a large salad as a first course helps a person eat less during the meal.9 In contrast, fat
has a weak effect on satiation; consequently, eating high-fat foods may lead to pas-
sive overconsumption. High-fat foods are flavorful, which stimulates the appetite
and entices people to eat more. High-fat foods are also energy dense; consequently,
they deliver more kcalories per bite. (Chapter 1 introduced the concept of energy den-
sity, and Chapter 9 describes how considering a food’s energy density can help with
weight management.) Although fat provides little satiation during a meal, it pro-
duces strong satiety signals once it enters the intestine. Fat in the intestine triggers the
release of cholecystokinin—a hormone that signals satiety and inhibits food intake.10
Eating high-fat foods while trying to limit energy intake requires small portion
sizes, which can leave a person feeling unsatisfied. Portion size correlates directly
with a food’s satiety. Instead of eating small portions of high-fat foods and feeling
Physiological influences
• Empty stomach
• Gastric contractions
• Absence of nutrients in small intestine
• GI hormones
• Endorphins (the brain’s pleasure chemicals)
are triggered by the smell, sight, or taste of foods,
enhancing the desire for them
Postingestive influences
(after food enters the digestive tract)
• Food in stomach triggers
stretch receptors
• Nutrients in small intestine
elicit hormones (for example, fat
elicits cholecystokinin, which slows
gastric emptying)
Postabsorptive influences
(after nutrients enter the blood)
• Nutrients in the blood signal the brain (via
nerves and hormones) about their availability,
use, and storage
• As nutrients dwindle, satiety diminishes.
• Hunger develops
Sensory influences
• Thought, sight, smell,
sound, taste of food
Cognitive influences
• Presence of others,
social stimulation
• Perception of hunger,
awareness of fullness
• Favorite foods, foods
with special meanings
• Time of day
• Abundance of
available food
Hunger
1
1
2
2
3
3
4
4
5
5 Satiety: Several
hours later
Keep eating
Satiation:
End meal
Seek food
and start meal
© Banana Stock, Ltd./Jupiter Images
©
Creatas/Jupiter
Images
©
Creatas/Jupiter
Images
©
Benefox
Press/Corbis
FIGURE 8-2 Hunger, Satiation, and Satiety
satiating: having the power to suppress
hunger and inhibit eating.

deprived, a person can feel satisfied by eating large portions of high-protein and
high-fiber foods. Figure 8-3 illustrates how fat influences portion size.
Message Central—The Hypothalamus As you can see, eating is a complex be-
havior controlled by a variety of psychological, social, metabolic, and physiological
factors. The hypothalamus appears to be the control center, integrating messages
about energy intake, expenditure, and storage from other parts of the brain and
from the mouth, GI tract, and liver. Some of these messages influence satiation,
which helps control the size of a meal; others influence satiety, which helps deter-
mine the frequency of meals.
Dozens of chemicals in the brain participate in appetite control and energy bal-
ance. By understanding the action of these brain chemicals, researchers may one day
be able to control appetite. The greatest challenge now is to sort out the many actions
of these brain chemicals. For example, one of these chemicals, neuropeptide Y,
causes carbohydrate cravings, initiates eating, decreases energy expenditure, and in-
creases fat storage—all factors favoring a positive energy balance and weight gain.
Regardless of hunger, people typically overeat
when offered the abundance and variety of an
“all you can eat” buffet.
For the same size portion, peanuts deliver more than 15 times the
kcalories and 20 times the fat of popcorn.
For the same number of kcalories, a person can have a few
high-fat peanuts or almost 2 cups of high-fiber popcorn. (This
comparison used oil-based popcorn; using air-popped popcorn
would double the amount of popcorn in this example.)
837 kcal
71 g fat
55 kcal
3 g fat
100 kcal
9 g fat
100 kcal
5 g fat
FIGURE 8-3 How Fat Influences Portion Sizes
A mixture of signals governs a person’s eating behaviors. Hunger and appetite
initiate eating, whereas satiation and satiety stop and delay eating, respec-
tively. Each responds to messages from the nervous and hormonal systems.
Superimposed on these signals are complex factors involving emotions,
habits, and other aspects of human behavior.
IN SUMMARY
Energy Out: The kCalories the Body
Expends
Chapter 7 explained that heat is released whenever the body breaks down carbohy-
drate, fat, or protein for energy and again when that energy is used to do work. The
generation of heat, known as thermogenesis, can be measured to determine the
amount of energy expended. ◆ The total energy a body expends reflects three main
categories of thermogenesis:
• Energy expended for basal metabolism
• Energy expended for physical activity
◆ Energy expenditure, like food energy, can
be determined by:
• Direct calorimetry, which measures
the amount of heat released
• Indirect calorimetry, which measures
the amount of oxygen consumed and
carbon dioxide expelled
neuropeptide Y: a chemical produced in the
brain that stimulates appetite, diminishes
energy expenditure, and increases fat
storage.
thermogenesis: the generation of heat; used
in physiology and nutrition studies as an
index of how much energy the body is
expending.
©
Owen
Franken/CORBIS
©
Polara
Studios
Inc.
(both)

254 • CHAPTER 8
• Energy expended for food consumption
A fourth category is sometimes involved:
• Energy expended for adaptation
Components of Energy Expenditure
People expend energy when they are physically active, of course, but they also ex-
pend energy when they are resting quietly. In fact, quiet metabolic activities account
for the lion’s share of most people’s energy expenditures, as Figure 8-4 shows.
Basal Metabolism About two-thirds of the energy the average person expends in
a day supports the body’s basal metabolism. Metabolic activities maintain the
body temperature, keep the lungs inhaling and exhaling air, the bone marrow mak-
ing new red blood cells, the heart beating 100,000 times a day, and the kidneys fil-
tering wastes—in short, they support all the basic processes of life.
The basal metabolic rate (BMR) is the rate at which the body expends en-
ergy for these maintenance activities. ◆ The rate may vary dramatically from per-
son to person and may vary for the same individual with a change in circumstance
or physical condition. The rate is slowest when a person is sleeping undisturbed,
but it is usually measured in a room with a comfortable temperature when the per-
son is awake, but lying still, after a restful sleep and an overnight (12 to 14 hour)
fast. A similar measure of energy output—called the resting metabolic rate
(RMR)—is slightly higher than the BMR because its criteria for recent food intake
and physical activity are not as strict.
In general, the more a person weighs, the more total energy is expended on
basal metabolism, but the amount of energy per pound of body weight may be
lower. For example, an adult’s BMR might be 1500 kcalories per day and an in-
fant’s only 500, but compared to body weight, the infant’s BMR is more than twice
as fast. Similarly, a normal-weight adult may have a metabolic rate one and a half
times that of an obese adult when compared to body weight because lean tissue is
metabolically more active than body fat.
Table 8-1 summarizes the factors that raise and lower the BMR. For the most
part, the BMR is highest in people who are growing (children, adolescents, and
pregnant women) and in those with considerable lean body mass (physically fit
people and males). One way to increase the BMR then is to participate in en-
durance and strength-training activities regularly to maximize lean body mass.
The BMR is also high in people with fever or under stress and in people with highly
active thyroid glands. The BMR slows down with a loss of lean body mass and dur-
ing fasting and malnutrition.
Physical Activity The second component of a person’s energy output is physical
activity: voluntary movement of the skeletal muscles and support systems. Physi-
cal activity is the most variable—and the most changeable—component of energy
expenditure. Consequently, its influence on both weight gain and weight loss can
be significant.
During physical activity, the muscles need extra energy to move, and the heart
and lungs need extra energy to deliver nutrients and oxygen and dispose of
wastes. The amount of energy needed for any activity, whether playing tennis or
studying for an exam, depends on three factors: muscle mass, body weight, and
activity. The larger the muscle mass and the heavier the weight of the body part
being moved, the more energy is expended. Table 8-2 gives average energy expen-
ditures for various activities. The activity’s duration, frequency, and intensity also
influence energy expenditure: the longer, the more frequent, and the more intense
the activity, the more kcalories expended. (An activity’s duration, frequency, and
intensity also influence the body’s use of the energy-yielding nutrients.)
Thermic Effect of Food When a person eats, the GI tract muscles speed up their
rhythmic contractions, the cells that manufacture and secrete digestive juices
basal metabolism: the energy needed to
maintain life when a body is at complete
digestive, physical, and emotional rest.
basal metabolic rate (BMR): the rate of
energy use for metabolism under specified
conditions: after a 12-hour fast and restful
sleep, without any physical activity or
emotional excitement, and in a comfortable
setting. It is usually expressed as kcalories per
kilogram body weight per hour.
resting metabolic rate (RMR): similar to the
basal metabolic rate (BMR), a measure of the
energy use of a person at rest in a comfortable
setting, but with less stringent criteria for
recent food intake and physical activity.
Consequently, the RMR is slightly higher
than the BMR.
lean body mass: the body minus its fat
content.
30-50%
Physical
activities
10%
Thermic effect
of food 50-65%
Basal metabolism
FIGURE 8-4 Components of Energy
Expenditure
The amount of energy spent in a day
differs for each individual, but in gen-
eral, basal metabolism is the largest
component of energy expenditure and
the thermic effect of food is the small-
est. The amount spent in voluntary
physical activities has the greatest vari-
ability, depending on a person’s activity
patterns. For a sedentary person, physi-
cal activities may account for less than
half as much energy as basal metabo-
lism, whereas an extremely active per-
son may expend as much on activity as
for basal metabolism.
◆ Quick and easy estimates for basal energy
needs:
• Men: Slightly 1 kcal/min (1.1 to 1.3
kcal/min) or 24 kcal/kg/day
• Women: Slightly 1 kcal/min (0.8 to 1.0
kcal/min) or 23 kcal/kg/day
For perspective, a burning candle or a 75-
watt light bulb releases about 1 kcal/min.

TABLE 8-1 Factors that Affect the BMR
Factor Effect on BMR
Age Lean body mass diminishes with age, slowing the BMR.a
Height In tall, thin people, the BMR is higher.b
Growth In children and pregnant women, the BMR is higher.
Body composition (gender) The more lean tissue, the higher the BMR (which is why males
usually have a higher BMR than females). The more fat tissue, the
lower the BMR.
Fever Fever raises the BMR.c
Stresses Stresses (including many diseases and certain drugs) raise the BMR.
Environmental Both heat and cold raise the BMR.
temperature
Fasting/starvation Fasting/starvation lowers the BMR.d
Malnutrition Malnutrition lowers the BMR.
Hormones (gender) The thyroid hormone thyroxin, for example, can speed up or slow
down the BMR.e Premenstrual hormones slightly raise the BMR.
Smoking Nicotine increases energy expenditure.
Caffeine Caffeine increases energy expenditure.
Sleep BMR is lowest when sleeping.
aThe BMR begins to decrease in early adulthood (after growth and development cease) at a rate of about 2 percent/decade. A
reduction in voluntary activity as well brings the total decline in energy expenditure to 5 percent/decade.
bIf two people weigh the same, the taller, thinner person will have the faster metabolic rate, reflecting the greater skin surface,
through which heat is lost by radiation, in proportion to the body’s volume (see the margin drawing on p. 256).
cFever raises the BMR by 7 percent for each degree Fahrenheit.
dProlonged starvation reduces the total amount of metabolically active lean tissue in the body, although the decline occurs
sooner and to a greater extent than body losses alone can explain. More likely, the neural and hormonal changes that accom-
pany fasting are responsible for changes in the BMR.
eThe thyroid gland releases hormones that travel to the cells and influence cellular metabolism. Thyroid hormone activity can
speed up or slow down the rate of metabolism by as much as 50 percent.
TABLE 8-2 Energy Expended on Various Activities
The values listed in this table reflect both the energy expended in physical activity and the amount used for BMR.
To calculate kcalories spent per minute of activity for your own body weight, multiply kcal/lb/min (or
kcal/kg/min) by your exact weight and then multiply that number by the number of minutes spent in the
activity. For example, if you weigh 142 pounds, and you want to know how many kcalories you spent doing
30 minutes of vigorous aerobic dance: 0.062 142 8.8 kcalories per minute; 8.8 30 minutes 264
total kcalories spent.
kCal/lb kCal/kg
Activity min min
Aerobic dance
(vigorous) .062 .136
Basketball
(vigorous,
full court) .097 .213
Bicycling
13 mph .045 .099
15 mph .049 .108
17 mph .057 .125
19 mph .076 .167
21 mph .090 .198
23 mph .109 .240
25 mph .139 .306
Canoeing, flat
water, moderate
pace .045 .099
Cross-country skiing
8 mph .104 .229
Gardening .045 .099
Golf (carrying
clubs) .045 .099
kCal/lb kCal/kg
Activity min min
Handball .078 .172
Horseback
riding (trot) .052 .114
Rowing
(vigorous) .097 .213
Running
5 mph .061 .134
6 mph .074 .163
7.5 mph .094 .207
9 mph .103 .227
10 mph .114 .251
11 mph .131 .288
Soccer (vigorous) .097 .213
Studying .011 .024
Swimming
20 yd/min .032 .070
45 yd/min .058 .128
50 yd/min .070 .154
kCal/lb kCal/kg
Activity min min
Table tennis
(skilled) .045 .099
Tennis (beginner) .032 .070
Vacuuming and
other household
tasks .030 .066
Walking (brisk pace)
3.5 mph .035 .077
4.5 mph .048 .106
Weight lifting
light-to-moderate
effort .024 .053
vigorous effort .048 .106
Wheelchair
basketball .084 .185
Wheeling self in
wheelchair .030 .066

256 • CHAPTER 8
begin their tasks, and some nutrients are absorbed by active transport. This accel-
eration of activity requires energy and produces heat; it is known as the thermic
effect of food (TEF).
The thermic effect of food is proportional to the food energy taken in and is usu-
ally estimated at 10 percent of energy intake. Thus a person who ingests 2000
kcalories probably expends about 200 kcalories on the thermic effect of food. The
proportions vary for different foods, however, and are also influenced by factors
such as meal size and frequency. In general, the thermic effect of food is greater for
high-protein foods than for high-fat foods ◆ and for a meal eaten all at once
rather than spread out over a couple of hours. Some research suggests that the
thermic effect of food is reduced in obese people and may contribute to their effi-
cient storage of fat.11 For most purposes, however, the thermic effect of food can be
ignored when estimating energy expenditure because its contribution to total en-
ergy output is smaller than the probable errors involved in estimating overall en-
ergy intake and output.
Adaptive Thermogenesis Some additional energy is spent when a person must
adapt to dramatically changed circumstances (adaptive thermogenesis). When
the body has to adapt to physical conditioning, extreme cold, overfeeding, starva-
tion, trauma, or other types of stress, it has extra work to do, building the tissues and
producing the enzymes and hormones necessary to cope with the demand. In some
circumstances, this energy makes a considerable difference in the total energy ex-
pended. Because this component of energy expenditure is so variable and specific to
individuals, it is not included when calculating energy requirements.
Estimating Energy Requirements
In estimating energy requirements, the DRI Committee developed equations that
consider how the following factors influence energy expenditure: ◆
• Gender. In general, women have a lower BMR than men, in large part be-
cause men typically have more lean body mass. Two sets of energy equa-
tions—one for men and one for women—were developed to accommodate
the influence of gender on energy expenditure.
• Growth. The BMR is high in people who are growing. For this reason, preg-
nant and lactating women, infants, children, and adolescents have their
own sets of energy equations (see Appendix F).
• Age. The BMR declines during adulthood as lean body mass diminishes. This
change in body composition occurs, in part, because some hormones that
influence appetite, body weight, and metabolism become more, or less, ac-
tive with age.12 Physical activities tend to decline as well, bringing the aver-
age reduction in energy expenditure to about 5 percent per decade. The
decline in the BMR that occurs when a person becomes less active reflects the
loss of lean body mass and may be minimized with ongoing physical activ-
ity. Because age influences energy expenditure, it is also factored into the en-
ergy equations.
• Physical activity. Using individual values for various physical activities (as in
Table 8-2) is time-consuming and impractical for estimating the energy
needs of a population. Instead, various activities are clustered according to
the typical intensity of a day’s efforts. Energy equations include a physical
activity factor for various levels of intensity for each gender.
• Body composition and body size. The BMR is high in people who are tall and
so have a large surface area. ◆ Similarly, the more a person weighs, the
more energy is expended on basal metabolism. For these reasons, the energy
equations include a factor for both height and weight.
As just explained, energy needs vary between individuals depending on such
factors as gender, growth, age, physical activity, and body size and composition.
◆ Each of these structures is made of 8 blocks.
They weigh the same, but they are arranged
differently. The short, wide structure has 24
sides and the tall, thin one has 34. Because
the tall, thin structure has a greater surface
area, it will lose more heat (expend more
energy) than the short, wide one. Similarly,
two people of different heights might weigh
the same, but the taller, thin one will have a
higher BMR (expending more energy)
because of the greater skin surface.
thermic effect of food (TEF): an estimation
of the energy required to process food (digest,
absorb, transport, metabolize, and store
ingested nutrients); also called the specific
dynamic effect (SDE) of food or the
specific dynamic activity (SDA) of food.
The sum of the TEF and any increase in the
metabolic rate due to overeating is known as
diet-induced thermogenesis (DIT).
adaptive thermogenesis: adjustments in
energy expenditure related to changes in
environment such as extreme cold and to
physiological events such as overfeeding,
trauma, and changes in hormone status.
◆ Thermic effect of foods:
• Carbohydrate: 5–10%
• Fat: 0–5%
• Protein: 20–30%
• Alcohol: 15–20%
The percentages are calculated by dividing
the energy expended during digestion and
absorption (above basal) by the energy con-
tent of the food.
◆ Note that Table 8-1 (p. 255) lists these fac-
tors among those that influence BMR and
consequently energy expenditure.

A person in energy balance takes in energy from food and expends much of it
on basal metabolic activities, some of it on physical activities, and a little on
the thermic effect of food. Because energy requirements vary from person to
person, such factors as gender, age, weight, and height as well as the intensity
and duration of physical activity must be considered when estimating energy
requirements.
IN SUMMARY
To determine your estimated energy require-
ments (EER), use the appropriate equation,
inserting your age in years, weight (wt) in
kilograms, height (ht) in meters, and physi-
cal activity (PA) factor from the accompany-
ing table. (To convert pounds to kilograms,
divide by 2.2; to convert inches to meters,
divide by 39.37.)
• For men 19 years and older:
EER [662 (9.53 age)] PA
[(15.91 wt) (539.6 ht)]
• For women 19 years and older:
EER [354 (6.91 age)] PA
[(9.36 wt) (726 ht)]
For example, consider an active 30-year-
old male who is 5 feet 11 inches tall and
weighs 178 pounds. First, he converts his
weight from pounds to kilograms and his
height from inches to meters, if necessary:
178 lb 2.2 80.9 kg
71 in 39.37 1.8 m
Next, he considers his level of daily physical
activity and selects the appropriate PA factor
from the accompanying table. (In this exam-
ple, 1.25 for an active male.) Then, he inserts
his age, PA factor, weight, and height into the
appropriate equation:
EER [662 (9.53 30)] 1.25
[(15.91 80.9) (539.6 1.8)]
(A reminder: Do calculations within the paren-
theses first.) He calculates:
EER [662 286] 1.25 [1287 971]
(Another reminder: Do calculations within the
brackets next.)
EER = 376 1.25 2258
(One more reminder: Do multiplication
before addition.)
EER 376 2823
EER 3199
The estimated energy requirement for an
active 30-year-old male who is 5 feet 11
inches tall and weighs 178 pounds is about
3200 kcalories/day. His actual requirement
probably falls within a range ◆ of 200 kcalo-
ries above and below this estimate.
NOTE: Appendix F provides EER equations for
infants, children, adolescents, and pregnant
women.
HOW TO Estimate Energy Requirements
Physical Activity (PA) Factors for EER Equations
Men Women Physical Activity
Sedentary 1.0 1.0 Typical daily living activities
Low active 1.11 1.12 Plus 30–60 min moderate activity
Active 1.25 1.27 Plus 60 min moderate activity
Very active 1.48 1.45 Plus 60 min moderate activity and 60 min
vigorous or 120 min moderate activity
NOTE: Moderate activity is equivalent to walking at 3 to 41/2 mph.
It feels like work and it may make you tired,
but studying requires only one or two kcalories
per minute.
©
Bob
Torrez/Stone/Getty
Images
Even when two people are similarly matched, however, their energy needs still dif-
fer because of genetic differences. Perhaps one day genetic research will reveal how
to estimate requirements for each individual. For now, the accompanying “How to”
provides instructions on calculating your estimated energy requirements using the
DRI equations and physical activity factors. ◆
◆ For most people, the actual energy require-
ment falls within these ranges:
• For men, EER ± 200 kcal
• For women, EER ± 160 kcal
For almost all people, the actual energy
requirement falls within these ranges:
• For men, EER ± 400 kcal
• For women, EER ± 320 kcal
To practice estimating energy requirements, log on
to academic.cengage.com/login, go to Chapter 8,
then go to How To.
◆ Appendix F presents DRI tables that pro-
vide

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