The degree of energy required by the body depends very largely upon the amount of work or activity it undergoes, hence the amount of food required to supply this activity cannot be accurately prescribed when the degree of required energy is unknown. However, there is a certain amount of work performed by the beating of the heart and in the maintenance of body-heat which can be fairly well estimated. The quantity of energy-yielding food required, each twenty-four hours, for the maintenance of the activities of life is about one vieno for every ten pounds of body-weight. For a man at steady muscular work, such as a carpenter or a farmer, this quantity should be about doubled. The quantity required by a man of sedentary habits, but who takes regular exercise for an hour or two each day, is about half way between these two amounts. Thus, a man weighing one hundred forty pounds would require one and one-half vienos for each ten pounds, or twenty-one vienos of food each day. These weights apply only to people of normal flesh, who desire neither to gain nor to lose.

Quantity of food required for various occupations.

The fact that either fat or carbohydrates can be used as a source of muscular energy may be taken advantage of in prescribing dietaries for persons whose digestive organs are so impaired that they cannot digest a normal quantity of either of these nutrients, but who could digest a small quantity of either. This does not mean, however, that the proportion of fat and of carbohydrates in the food can be disregarded. The digestive processes involved are radically different, hence a suitable proportion of carbohydrates and fats should always be maintained.

With a view to guiding in a general way those who wish to adopt a standard of diet for ordinary use, and who consult tables in which fats and carbohydrates are listed separately, I might state that the fat should form about one-eighth the total source of energy, or one-sixteenth the weight of all water-free (solid) food eaten. Until forty years ago the idea was held by scientists, and is still a matter of popular belief, that nitrogenous foods are the sole source of all muscular energy. This is quite a natural assumption. Lean meat is muscle. If a man eats the muscle of another animal, by the primitive process of reasoning, he should acquire muscle. This belief among people who are not acquainted with physiological chemistry is almost universal, while the facts are, the man who eats the muscle of an ox for the purpose of adding strength to his own biceps is acting no more wisely than the college boy who takes calf's brain for breakfast the day before examination.

Proportion of fat required under ordinary conditions.

Fallacy of lean meat producing muscle.

The fact that nitrogenous foods are not a source of muscular energy has been repeatedly proved by experiments on man and animals too numerous to relate here. The sugar and the fat in the blood are taken into the muscle-cells, and there unite with the oxygen brought from the lungs, producing energy. When the body is fed upon proteids lacking a sufficient quantity of other food elements, a portion of this proteid is converted into glucose or sugar, which maintains body-heat and energy. This is what happens in the case of carnivorous animals that have excretory organs especially adapted to the converting and the eliminating of useless or surplus products.

Nitrogenous foods not a source of muscular energy.

It has been proved that dogs are capable of living for an indefinite period of time upon a diet containing only a small proportion of proteid matter, while maintaining health and increasing in weight. Thus we see that even carnivorous animals require, for the maintenance of the body-functions, a comparatively small amount of nitrogenous material. Their strength and heat-forming elements can be secured from carbohydrates and fats, probably to their actual benefit. It is interesting to note, however, that dogs as a general rule cannot live and thrive on a vegetable diet; a certain amount of animal proteids seems indispensable. The same principle applies to other carnivorous animals. Even ducks and chickens need a small percentage of animal proteids in order to properly thrive and develop.

In order to maintain good health, every person requires a certain amount of nitrogen, the quantity being governed by activity, exposure, age, and temperature of environment. The growing youth needs nitrogen to supply material for the tissue growth of his body; an emaciated person who wishes to increase weight, a person recovering from illness, or a man who is constantly performing strenuous work, would all require a generous quantity of nitrogenous food. The lowest possible nitrogen requirement for one of normal weight has been determined by various methods to be from 40 to 60 decigrams per day. This quantity, however, is the actual amount that is used in the body-processes, and should be increased according to activity or exposure to the open air.

Small amount of proteid matter required by animals.

From the results of numerous experiments under normal activity, the quantity of nitrogenous food estimated to maintain the best bodily condition is about three-fourths of a decigram for each pound of body-weight; less than one-half of a decigram per pound of body-weight would cause nitrogen starvation, while more than one decigram per pound, except in the cases just mentioned, would result only in thrusting needless work upon the liver and the kidneys, whose duties are to guard the body against the results of incorrect eating. There are certain conditions under which this amount of nitrogen may be exceeded in order to gain definite and specific purposes, but in such cases the nature of the proteid is of great importance. In certain occupations, for instance sedative labor, the most soluble proteids, such as egg albumin (white of eggs), milk, and green peas and beans should be selected; while in cases of heavy manual labor, the heavier proteids, such as nuts, cheese, dried legumes, fish and fowl should be selected.

Conditions governing quantity of nitrogen.

Lowest daily amount of nitrogen required.

Amount of nitrogen required by the body.