FOOD VALUE
22. Nearly all foods are complex substances, and they differ from one another in what is known as their value, which is measured by the work the food does in the body either as a tissue builder or as a producer of energy. However, in considering food value, the person who prepares food must not lose sight of the fact that the individual appetite must be appealed to by a sufficient variety of appetizing foods. There would be neither economy nor advantage in serving food that does not please those who are to eat it.
While all foods supply the body with energy, they differ very much in the quantity they yield. If certain ones were chosen solely for that purpose, it would be necessary for any ordinary person to consume a larger quantity of them than could be eaten at any one time. For instance, green vegetables furnish the body with a certain amount of energy, but they cannot be eaten to the exclusion of other things, because no person could eat in a day a sufficient amount of them to give the body all the energy it would need for that day's work. On the other hand, certain foods produce principally building material, and if they were taken for the purpose of yielding only energy, they would be much too expensive. Meats, for example, build up the body, but a person's diet would cost too much if meat alone were depended on to provide the body with all the energy it requires. Many foods, too, contain mineral salts, which, as has been pointed out, are needed for building tissue and keeping the body in a healthy condition.
23. To come to a correct appreciation of the value of different foods, it is necessary to understand the unit employed to measure the amount of work that foods do in the body. This unit is the CALORIE, orcalory, and it is used to measure foods just as the inch, the yard, the pound, the pint, and the quart are the units used to measure materials and liquids; however, instead of measuring the food itself, it determines its food value, or fuel value. To illustrate what is meant, consider, for instance, 1/2 ounce of sugar and 1/2 ounce of butter. As far as the actual weight of these two foods is concerned, they are equal; but with regard to the work they do in the body they differ considerably. Their relative value in the body, however, can be determined if they are measured by some unit that can be applied to both. It is definitely known that both of them produce heat when they are oxidized, that is, when they are combined with oxygen; thus, the logical way of measuring them is to determine the quantity of heat that will be produced when they are eaten and united with oxygen, a process that causes the liberation of heat. The calorie is the unit by which this heat can be measured, it being the quantity of heat required to raise the temperature of 1 pint of water 4 degrees Fahrenheit, which is the name of the thermometer commonly used in the home. When burned as fuel, a square of butter weighing 1/2 ounce produces enough heat to raise 1 pint of water 400 degrees Fahrenheit, and it will yield the same amount of heat when it is eaten and goes through the slow process of oxidation in the body. On the other hand, 1/2 ounce of sugar upon being oxidized will produce only enough heat to raise the temperature of 1 pint of water about 230 degrees Fahrenheit. Thus, as will be seen, 1/2 ounce of butter has a value of approximately 100 calories, whereas 1/2 ounce of sugar contains only about 57-1/2 calories.
Other foods yield heat in varying degrees, and their food value is determined in exactly the same way as that of butter and sugar. To give an idea of the composition of various food materials, as well as the number of calories that 1 pound of these food materials will yield, food charts published by the United States Department of Agriculture are here presented. As an understanding of these charts will prove extremely profitable in the selection of food, a careful study of them at this time is urged. In addition, reference to them should be made from time to time as the various kinds of foods are taken up, as the charts will then be more easily comprehended and their contents of more value.