Regardless of physical activity, your body uses up to 70 percent of its daily energy expenditure simply by keeping organs working, replacing cells, repairing damage, and building tissue. Foods have different energy, or caloric, values because they contain different combinations and varying amounts of protein, fat, and carbohydrates. When food is oxidized, or burned, the energy, or heat, that it produces is measured in units called calories. The basic nutrients in food – carbohydrates, protein, and fat – differ in the amount of energy that they supply. A gram of either pure carbohydrate or pure protein contains 4 calories; a gram of pure fate, however, contains 9 calories, or more than twice as many. The other elements in food, water, and fiber, supply no energy. This is why, a 1 ¾ ounce serving of cauliflower, which is high in fiber and water, will supply only 7 calories, whereas a whole-wheat roll of the same weight will provide 135 calories. Everybody needs a certain amount of energy from food simply to maintain basic bodily functions such as breathing, blood circulation, and body temperature when the body is at rest. This called the basal metabolic rate, or BMR. Further calories are necessary for activities. The number of calories each individual requires varies, depending on age, sex, size, metabolic rate, and activity. |
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