Personal hygiene and physical training for women

by Anna M. Galbraith

But to enable the body to continue to perform these functions indefinitely it must be properly fed, and a proper feeding of the body requires a knowledge of its composition and the exchanges which are constantly going on. This knowledge is to be derived from a study of its metabolism, the analysis of foods, and a determination of their heat values.

The Classification of Foods.—Foods are divided into proteins, carbohydrates, fats, mineral salts, and water. The body is composed of materials belonging to the same groups. Proteins form the principal part of muscles, bones, and many other tissues of animal bodies; they also constitute some of the most important vegetable structures.

Proteins are probably the most complex compounds in nature; all contain carbon, hydrogen, oxygen, and nitrogen, generally sulphur, and sometimes phosphorus also. They are, with rare exceptions, colloids, that is, glue-like, non-crystalline bodies, which even in solution cannot pass through animal membranes.

The building stones of the body are the amino-acids. All proteins contain them, but the kinds and proportions are not always the same. It has been shown by biologic experiments that life and growth cannot be maintained when certain amino-acids are deficient.

Proteins are of use to the human body as tissue formers, and, secondly, as producers of energy, but they also have a food value as flavoring agents, rendering the food appetizing, and so are to a certain extent stimulants. The palatability of meats and soups are due to their presence. The amino-acids have decided heat value.

The necessity for proteins in the diet has been abundantly demonstrated. Many investigations have shown that when the food contains no protein the waste of nitrogen continues, no matter how abundant the supply of carbohydrates and fats. In other words, a continuous protein cleavage is demanded by the animal organism, and no other nutriments can serve as a substitute for protein to meet this demand. If the food contains no protein, the body tissues will be depleted. It cannot be said that carbohydrates or fats are an essential part of the diet in the sense that protein is, because it is possible to substitute one for the other to produce energy, or to substitute proteins for both.

In spite of these facts, it is safe to assert that the welfare of the human organism is best promoted by a mixed diet, including all three classes of food. The larger part of man’s food is used for the production of energy, and it is physiologically economic that this energy be supplied by the non-nitrogenous nutrients, particularly the carbohydrates, and to allocate to protein, so far as practicable, its special rôle of building material.

Nitrogenous Waste Products.—The end-product of proteins is urea, which is formed from protein decomposition products in relatively large amounts in the liver cells, and, being readily soluble and diffusible, is easily eliminated by the kidneys. Besides urea there are other smaller quantities of nitrogen compounds, the one most deserving of notice being uric acid.

When the proteins are broken down to supply energy, there is always a definite proportion of urea and uric acid residue that must be eliminated through the kidneys. An excessive protein diet would burden these organs beyond their accustomed habit, and flooding the system with these nitrogenous wastes increases the tendency to rheumatism and gout.

Uric acid is of general interest, and when present in the system in abnormally large amounts, as in gouty persons, has a pathologic significance. It is more complex in its composition, and, what is of particular importance, is that it does not readily dissolve. It forms very insoluble salts which have unpleasant tendencies to settle in the joints, causing great pain. Did its metabolism proceed properly, it should be resolved into urea and carbon dioxid. The quantity of uric acid that appears in the urine is the residue that has escaped this oxidation.