The property whereby a food produces heat and energy within the body may be expressed in terms of energy value. The unit customarily used by nutritionists for measuring human energy needs and expenditures and the energy value of foods is the kilocalorie, which is the amount of heat required to raise the temperature of 1 kg of water 1°C. (A calorie is the amount of heat required to warm 1 g of water 1°C.) Watt and Merrill (1963) cite the Atwater system (Atwater and Bryant, 1900), reviewed by a committee of the Food and Agriculture Organization of the United Nations, as being a satisfactory system for determining energy values of foods when correctly used. The system was developed working with human subjects to determine the available energy values for a wide variety of foods. The procedure is to adjust the heats of combustion of the fat, protein, and carbohydrates in a food to allow for the losses in digestion and metabolism found for human subjects, and to apply the adjusted calorie factors to the amounts of protein, fat, and carbohydrates in the food. The quantities of proteins and fat are determined by chemical analysis, and the percentage of carbohydrates is obtained by difference, the remainder after the sum of the fat, protein, ash and moisture has been subtracted from 100. (The U.S. Department of Agriculture (USDA) has published and makes available the details on derivation of the calorie factors.) The energy value of foods then represents the energy available after deductions have been made for losses in metabolism and digestion. The traditional method of evaluating the nutritive value of a food is to express its components in terms of nutrients, i.e., water, carbohydrates, fats, protein, minerals, and vitamins.
KeywordsMilk Protein Night Blindness Recommend Daily Allowance Invert Sugar Milk Sugar
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