This section is from the book "The Human Body: An Elementary Text-Book Of Anatomy, Physiology, And Hygiene", by H. Newell Martin. Also available from Amazon: The Human Body.
Since albuminous foods contain carbon, nitrogen, and hydrogen, life may be maintained on them if the necessary salts, water, and oxygen be also supplied; but such a diet would not be economical. Albumens contain in 100 parts about 52 of carbon and 15 of nitrogen, so a man fed on them alone would get about 3 1/2 parts of carbon for every 1 of nitrogen. His daily losses are not in this ratio, but about 13.7 parts of carbon to 1 of nitrogen; and to get enough carbon from albumens far more than the necessary amount of nitrogen must be taken. Of dry albumens 1 pound 2 1/2 ounces (527 grams) would yield the necessary carbon, but would contain 2| ounces (79 grams) of nitrogen, or four times more than is necessary to cover the daily losses of that element from the body. Fed on a purely albuminous diet a man would, therefore, have to digest a vast quantity to get enough carbon, and in eating and absorbing it, and in getting rid of the excess nitrogen (which is useless to him), a great deal of useless labor must be thrust upon the digestive and excretory organs. Were a man to live on bread alone he would force much unnecessary work on his organs. Bread contains little nitrogen in proportion to its carbon, and to get enough nitrogen far more carbon than could be utilized would have to be eaten, digested, and excreted daily.
What is the average daily loss of carbon from the body? Of nitrogen ? Does a man need hydrogen also in his food ? Why ?
On what group of foodstuffs can life be maintained without any others? Why is feeding entirely on albuminous substances not desirable?
The human race has discovered this fact: men use, where they have a choice, richly proteid substances to supply the nitrogen needed, but derive the carbon mainly from non-nitrogenous foods of the fatty or starch and sugary kinds, and so avoid excess of either nitrogen or carbon. For instance, lean beef contains about 1/4 of its weight of dry albumen, which albumen contains 15 per cent of nitrogen. Consequently 1 pound 3 ounces of lean meat Would supply the nitrogen needed to compensate for a day's losses. But the albumen contains 52 per cent of carbon, so the amount of it in the above weight of fatless meat would be 1070 grains (69 grams) or nearly 2 1/2 ounces, leaving 3150 grains (205 grams) or rather more than seven ounces, to be got either from fats or sugary and starchy substances. The necessary amount would be contained in 3940 grains (256 grams) or about 9 ounces of ordinary fats, or in 7080 grains (460 grams), a little over a pound, of starch; hence either of these with the above quantity of lean meat would form a far better diet both for the purse and the system than meat alone.
Explain why bread by itself would afford a bad diet.
Why do men use a mixed diet? Explain why lean meat alone would not be a good food. How could the deficient carbon of lean beef be supplied ?
Give illustrations of the fact that most foods contain more than one foodstuff.
As already pointed out, nearly all common foods contain several foodstuffs. Good butcher's meat, for example, contains nearly half its dry weight of fat: and bread in addition to proteids contains starch, fats, and sugar. In neither of them, however, are the foodstuffs mixed in the physiologically best proportions, and the custom of consuming several of them at each meal, or different ones at different meals during the day, is not only agreeable to the palate but in a high degree advantageous to the body. The strict vegetarians who do not eat even such substances as eggs, cheese, and milk, but confine themselves to a purely vegetable diet, which is always poor in albumens, take daily far more carbon than they require, and are to be congratulated on their excellent digestions which are able to stand the strain. Those so-called vegetarians who use eggs, cheese, etc., can of course get on very well, since such substances are extremely rich in albumens, and supply all the nitrogen needed, without the necessity of swallowing the vast bulk of food which must be eaten in order to get it directly from plants.
Why do we commonly use several foods at one meal? What element do strict vegetarians take in excess? How do nominal vegetarians get their nitrogen ?