Topics

Composition of foods.

Purposes served by the various food elements.

Digestion. Changes occurring in the mouth.

New discoveries in regard to saliva.

The effect of mastication upon the digestive process.

Taste and appetite as stimuli of the digestive secretions.

Other psychic influences in digestion.

Assimilation.

Poisonous properties of the body-waste.

Metabolism.

Quantities of food necessary to the maintenance of physical efficiency.

The old dietary standards.

The new standards.

IN order that the argument that follows can be readily understood, it is desirable that the reader should have a general working knowledge of the chemical composition of his foods, of the several purposes which the various food elements serve in the bodily economy, and of the different processes by which these purposes are accomplished.

All foods, whether animal or vegetable, are made up of three distinct classes of organic compounds known as proteid or nitrogenous or albuminous substances, carbohydrates, and fats; and of some fifteen different inorganic salts.1 Of these the pro-teid substances held the first place. They form the chemical basis of all living cells, and without them, there can be no life. They are the material which builds the body, which insures growth and which repairs tissue broken down by muscular exercise.

"The vital part of all tissue is proteid," says Professor Chittenden, "and only proteid can serve for its growth or renewal. .... Every living cell, whether of heart, muscle, brain or nerve, requires its due allowance of proteid material to maintain its physiological rhythm. No other foodstuff stands in such intimate relationship to the vital process"2

As has been said before, the foods which contain the highest percentages of proteid and which, therefore, are known as "proteid foods," are meat, fish, eggs, nuts, peas, beans, lentils and cheese; but there is no article of human diet except sugar and pure fat, into which it does not enter in a greater or less degree. Other things being equal, proteid seems to serve its purpose in the bodily economy equally well whether derived from the animal or from the vegetable kingdom.

1 Note - Proteid substances are characterized by containing about 16 per cent, of nitrogen. In addition, they contain on an average 52 per cent, of carbon, 7 per cent, of hydrogen, 23 per cent, of oxygen, and 0.5 - 2.0 per cent of sulphur . . . Carbohydrates . . . are entirely free from nitrogen, containing only carbon (44.4 per cent.), hydrogen (6.2 per cent.), and oxygen (49.4 per cent), and hence are classified as non-nitrogenous foods. - "Nutrition of Man," pp. 3-5.

2 Chittenden: "Nutrition of Man," pp. 4-5.

The carbohydrates and fats furnish the fuel for the body. They yield the heat that keeps it warm and the energy that enables it to do its work. While they are incapable of adding to the lean tissue without which the body cannot exist, they are able - when taken in excess of immediate fuel needs - to lay up a store of fat which the body can draw upon for its heat and energy whenever its food supply is cut off.

The carbohydrates are found chiefly in grains; in vegetables (other than peas, beans and lentils); and in fruits. All sweets and all "starchy" foods - of which the sweets are really only a form - belong in this class. For this reason the carbohydrates are frequently called " the starches and sugars."

Fats are found in almost all the proteid foods. There is no meat that is not streaked with them to a greater or less extent, and nuts are generously supplied with them in the form of oil. Of all the vegetables the "fattest" are the "legumes" - peas, beans, lentils and peanuts. Cheese is almost as rich in fat as it is in proteid. About the only foods which are prized primarily for their fats, are butter and vegetable oils.

Inorganic salts are required by the body for the building of bones and teeth, and for the regulation and control of the nutritive processes. They cannot build live tissue or furnish heat and energy, but they are essential as aids to digestion and assimilation. They are contained in all forms of food, but they exist in the vegetables in the greatest number and variety.

The following table, compiled by Professor Chittenden from data given in Bulletin 28 (Revised Edition) of U. S. Department of Agriculture, indicates the relative distribution of the various classes of food elements in some common articles of diet.

The Chemical Composition Of Some Common Food Materials

3 Chittenden: "Nutrition of Man," pp. 7-10.

In using this table, the fact should be borne in mind that foods containing equal quantities of the various food elements are not necessarily, because of their varying degrees of digestibility, of equal food value.

"For example," says Professor Chittenden, "roast mutton, cream cheese and dried peas contain approximately the same amount of proteid. Are we to infer that these three foods have the same nutritive value so far as proteid is concerned? Surely not, since no account is taken of the relative digestibility of the three foods. . . . In a general way it may be stated that with animal foods, such as meats, eggs, and milk, about 97 per cent, of the contained proteid is digested and thereby rendered available for the body. With ordinary vegetable foods, on the other hand, as they are usually prepared for consumption, only about 85 per cent, of the proteid is made available. This is partially due to the presence in the vegetable tissue of cellulose, which in some measure prevents that thorough attack of the proteid juices which occurs with animal foods. With a mixed diet, i e., with a variable admixture of animal and vegetable foods, it is usually considered that about 92 per cent. of the proteid contained therein will undergo digestion.