The fact that the energy requirement of the boy from 10 to 17 years is greater than that of the girl of equal age is due probably to the greater restlessness or muscular activity of the boy.
DAILY PROTEIN REQUIREMENT.—If a person's energy requirement were 2500 Calories, sufficient energy might be supplied by using butter or beef steak for a day's ration. Yet this would be extremely unpalatable and would not meet the needs of the body. The body should be nourished by all the combustible foodstuffs,—carbohydrates, fat, and protein. Now the question arises: How many of the required Calories shall be supplied by each of these foodstuffs?
Too much or too little protein is often harmful and produces serious results. As mentioned previously, too much protein may cause intestinal disturbances, and an overtaxing of the excretory organs. On the other hand, the use of too little protein may produce imperfect nourishment. Concerning the quantity of protein used in diet, there has been much difference of opinion. Atwater, an American authority, thought that there should be a generous supply, i.e. a surplus of protein, to supply the demands of body-building. Chittenden, another American authority, believes in just enough protein to meet the demands of the body. However, the use of sufficient protein food to produce from ten to fifteen per cent of the total Calories has been found both practical and satisfactory.
Daily Carbohydrate and Fat Requirement.—Although protein may furnish the body with energy, it should not serve as the principal source of fuel. Its more essential function is to help build the body. If carbohydrates and fat are present with protein, the former supply energy and allow the protein to perform its more important function of body-building. There should always be enough carbohydrates and fat to furnish energy to the body, so that the protein can be used chiefly for body-building. In the growing period of youth or after a wasting disease, it might seem that "flesh" could be "put on" by increasing the quantity of bodybuilding food. But such is not the case. The most effective work in building the body can be accomplished by using a normal amount of food rich in protein and a generous supply of foods rich in ash, carbohydrates, fat, and vitamines. With such a combination, the protein can be used to best advantage for body-building.
For practical purposes, the following general statement concerning the carbohydrates and fat requirement is believed to be adequate: If the total Calories and the number of Calories yielded by protein meet the requirement of a dietary standard and the food composing the diet is varied in composition, the carbohydrates and fat will exist in satisfactory proportion.
DAILY ASH REQUIREMENT.—Since ash is not a combustible foodstuff, it cannot be included in the foodstuffs whose energy requirement can be measured. Although ash exists in small quantity in food, the use of certain ash constituents is considered as necessary as the use of protein. A diet may meet the total energy, the protein, the carbohydrate, and the fat requirements, yet may be lacking in certain essential mineral materials. It is especially necessary to include food containing phosphorus, iron, and calcium in one's diet.
THE APPETITE AND FOOD REQUIREMENT.—The appetite is the most common measure of daily food requirement. If one relies upon his appetite as an index of the quantity of food he should consume, and if his health and weight remain normal, the appetite may serve as a guide for daily food requirement. But one may be a little over weight or under weight, and yet have normal body functions.
There can be no doubt, however, that the whims of the appetite often lead to unwise selection of food. A study of food composition is absolutely essential in overcoming this fault. Lack of energy or loss of flesh may be due to improper feeding. If the needs of the body and the kind and quantity of food that will supply these needs are understood by the home- keeper, she may do much in maintaining the health, happiness, and usefulness of the members of the family.
WEIGHT AS AN INDEX TO PROPER NOURISHMENT.—It has been found that the diet of an individual has a most decided effect upon his weight. Dr. Thomas D. Wood has prepared tables showing the normal height and weight of girls and boys of various ages. These tables are most valuable in determining whether or not a girl or boy is of the proper weight for his height. If the weight of a girl or boy is less than it should be, he is likely to be malnourished.