Nutrition involves the 3 main components of food: carbohydrates, proteins, and fats. Carbohydrates are the primary source of energy and are found in plants and their seeds. Proteins compose the structural components of living organisms and are found in foods like meats, eggs, milk, and beans. Fats are the preferred form of long term energy storage and are stored in fat cells; they are found in foods like oils. A balanced intake of carbohydrates, proteins, and fats provides the fuel the human body needs to function, while maintaining weight depends on balancing caloric intake with expenditure.