The energy the body uses is stored within the chemical bonds of certain nutrients. A calorie (kal′ ō-rē; heat) (cal) is the amount of energy (heat) necessary to raise the temperature of 1 gram (g) of water 1°C. A kilocalorie (kil′ ō-kal-ō-rē) (kcal) is 1000 cal and is used to express the larger amounts of energy supplied by foods and released through metabolism. For example, one slice of white bread contains about 75 kcal, 1 cup of whole milk contains 150 kcal, a banana contains 100 kcal, a hot dog contains 170 kcal (not counting the bun and dressings), a McDonald’s Big Mac has 540 kcal, and a soft drink adds another 145 kcal. For each gram of carbohydrate or protein metabolized by the body, about 4 kcal of energy are released. Fats contain more energy per unit of weight than carbohydrates and proteins, and they yield about 9 kcal/g. Table 17.1 lists the kilocalories supplied by some typi-cal foods. A typical diet in the United States consists of 50–60% carbohydrates, 35–45% fats, and 10–15% proteins. Table 17.1 also lists the carbohydrate, fat, and protein composition of some foods.
A kilocalorie is often called a Calorie (with a capital C). Unfortunately, this usage has resulted in confusion of the term calorie (with a lowercase c) with Calorie (with a capital C). Itis common practice on food labels to use the term calorie whenCalorie (kilocalorie) is the proper term.
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