As previously stated, one of the important functions of food is to provide the body with heat and energy. This is accomplished through the process of metabolism that functions in the following manner. In the various cells and tissues of the body, food substances, in combination with oxygen taken into the body through the lungs, are burned or oxidized, producing heat and energy. The heat that is generated is used for the control of body temperature, and the energy that is produced provides for the muscular activity and movements of the body.
The unit of measure of heat production is the calorie (cal). This is the amount of heat energy that is required to raise the temperature of 1 gram (g) of water 1 degree centigrade (C). In food chemistry and metabolism, the large calorie (kcal) is the unit of energy measurement used. One large calorie is 1000 times the size of a standard calorie. The amount of heat energy in terms of calories resulting from oxidation of foodstuffs is the caloric value of the food. By careful analysis, specific caloric values of the basic organic foods have been determined to be the following:
.1 g of PROTEIN yields 4 cal.
.1 g of CARBOHYDRATES yields 4 cal.
.1 g of FAT yields 9 cal.
Most foodstuffs are not pure basic elements, and the exact caloric value of the various compound foods containing more than one of each of the three basic elements cannot be determined precisely. However, laboratory determinations have provided relative caloric values of most representative foods. The following are a few typical examples:
It should be noted that alcoholic beverages provide 7 calories for each g of alcohol, but these calories have no nutritional value.
The basal metabolic rate (BMR) is an index of the energy demand of the body for the maintenance of life and body functions under basic conditions. Increased activity requires more fuel and oxygen in proportion to the degree of heat and energy requirements.
The energy requirements of a normal 150-pound man under situation of varying activity are approximated as follows:
Forms of activity --------- Calories
8 hours of sleep (60 calories per hour) .................480
3 hours of light exercise, going to and from work, etc. (200 calories per hour) ...........................600
8 hours of ward duty (220 calories per hour) ........................ 1,760
5 hours of recreation watching television (90 calories per hour x 5 = 450) swimming (500 calories per hour x 5 = 2,500) ..............4502,500
Total for the day ..... 3,290 5,340