257. Object.—Rational feeding of man has for its object the regulation of the food supply in accord with the demands of the body. It is based upon the same principles as the rational feeding of animals; in each, the best results in the way of health, amount of labor performed, and economy are secured when the body receives nutrients sufficient for the production of heat and energy and for the repair of worn-out tissues. Rational feeding is simply regulation of the food, both as to kind and amount, to meet the needs of the body.^[72]

258. Standard Rations.—In human feeding, as in animal feeding, it is not possible to lay down hard and fast rules as to the quantity of nutrients required for a standard ration.^[85] As stated in the chapter on Dietary Studies, such standards have been proposed, but they are to be considered as tentative rather than absolute, for the amount of food required by different persons must necessarily vary with the individuality. While it is impossible to establish absolute standards, any large variation from the provisional standards usually results in lessened ability to accomplish work, ill health, or increased expense.

259. Amounts of Food Consumed.—The approximate amounts of some food articles consumed per day are as follows:

In the calculation of rations it is desirable that the amount of any food article should not exceed that designated, unless for some special reason it has been found the food can consistently be increased. The amount of nutrients given in dietary standards is for one day, and the nutrients may be divided among the three meals as desired. It is to be noted that, ordinarily, the foods which supply carbohydrates are flour, corn meal, cereal products, potatoes, beans, sugar, and milk; those which supply fat are milk, butter, lard, and meats; and those which supply protein in liberal amounts are beans, cheese, meats, oatmeal, cereals, bread, and milk.

260. Average Composition of Foods.—The amounts of nutrients in foods are determined from the average composition of the foods. These figures for average composition are based upon analyses of a large number of samples of food materials.^[7] In individual cases it will be found that foods may vary from the standards given; as for example, milk may contain from 2.5 to 5 per cent of fat, while the protein and fat of meats vary appreciably from the figures given for average composition. With the cereals and vegetable foods, variations from the standards are small. In the table, the composition of the food as purchased represents all of the nutrients in the food, including those in the refuse, trimmings, or waste, while the figures for the edible portion represent the nutrients in the food after deducting what is lost as refuse. In making calculations, the student should use the figures given for the foods as purchased, unless the weights are of the edible portion only. The figures in the table are on the basis of percentage amounts, or nutrients in 100 pounds of food. By moving the decimal point two places to the left, the figures will represent the nutrients in one pound, and if this is multiplied by the number of pounds or fraction of a pound used, the quantity of nutrients is secured. For example, suppose bread contains 9.5 per cent of protein and 56 per cent of carbohydrates, 1 pound would contain 0.095 pound of protein, 0.56 pound of carbohydrates; and 0.5 of a pound would contain approximately 0.05 pound of protein and 0.28 pound of carbohydrates. In calculating rations, it is not necessary to carry the figures to the third decimal place.

Fig. 60.—Food Articles for a Human Ration.

261. Example of a Ration.—Suppose it is desired to calculate a ration for a man at light muscular work. First, note the requirements in the way of nutrients in the table "Dietary Standards," Section 246. Such a ration should supply approximately 0.22 pound each of protein and fat, and 0.77 pound of carbohydrates, and should yield 2800 calories. A trial ration is made by combining the following:

The quantities of nutrients in these food materials are approximately as follows:

Ration for Man at Moderate Work

It is to be noted that this ration contains approximately the amount of protein called for in the standard ration, while the fat is slightly more and the carbohydrates are less. The food value of the ration is practically that called for in the standard. This ration is sufficiently near the standard to supply the nutrient requirements of a man at light muscular work. To supply palatability, some fruit and vegetables should be added to the ration. These will contribute but little to the nutrient content, but are necessary in order to secure health and the best returns from the other foods, and as previously stated, they are not to be estimated entirely upon the basis of nutrient content. A number of food articles could be substituted in this ration, if desired, either in the interests of economy, palatability, or personal preference.

262. Requisites of a Balanced Ration.—Reasonable combinations of foods should be made to form balanced rations.^[2] A number of foods slow of digestion, or which require a large amount of intestinal work, should not be combined; neither should foods which are easily digested and which leave but little indigestible residue. After a ration has been calculated and found to contain the requisite amount of nutrients, it should be critically examined to see whether or not it fulfills the following requirements:

As explained in the chapter on Dietary Studies, the nutrients should be supplied from a number of foods rather than from a few, because it is believed the various nutrients, particularly the proteins, are not absolutely identical from all sources, or equal in nutritive value.

EXAMPLES

1. Calculate a ration for a man with little physical exercise.

2. Calculate a ration for a man at hard muscular labor, and give the approximate cost of the ration.

3. Calculate the amounts of food and the nutrient requirements for a family of seven for 10 days; five of the family to consume 0.8 as much as an adult. Calculate the cost of the food; then calculate on the same basis the probable cost of food for one year, adding 20 per cent for fluctuation in market price and additional foods not included in the list.

4. Weigh out the food articles used in problem No. 2, and apportion them among three meals.