Other investigators, however, have found no great difficulty in establishing nitrogenous equilibrium in man with much lower quantities of proteid food. Thus, Klemperer[18] found in the case of two young men of 64 and 65.5 kilos body-weight respectively, in an experiment lasting eight days, that nitrogenous equilibrium was established on 4.38 and 3.58 grams of nitrogen per day, but with a daily diet containing in addition to the small amount of proteid 264 grams of fat, 470.4 grams of carbohydrate, and 172 grams of alcohol, with a total fuel value of 5020 large calories.
Peschel,[19] too, has reported experimental results showing that he was able to establish nitrogenous equilibrium for a brief period with 7 grams of nitrogen daily, 5.31 grams appearing in the urine and 1.58 grams in the fæces.
Caspari and Glaessner,[20] in a five-days’ experiment with two vegetarians, found that the wife consumed daily, on an average, 5.33 grams of nitrogen, with fats and carbohydrates to equal 2715 calories, while the man took in 7.82 grams of nitrogen and 4559 calories. Both persons laid on nitrogen in spite of the low intake of proteid food.
Siven’s[21] experiments, however, are perhaps worthy of more careful consideration. Of 60 kilos body-weight and 30½ years of age, his experiments conducted on himself extended through thirty-two days with establishment of nitrogenous equilibrium on 6.26 grams of nitrogen. Moreover, in another experiment he was in nitrogen equilibrium for a day or two at least on 4.5 grams of nitrogen. In Siven’s experiment, the most noticeable feature is the added fact that the total intake of food per day was comparatively low, with a fuel value of only 2444 large calories. In this connection we may call attention to the recent experiments of Landergren,[22] who found with four individuals fed on a daily diet containing only 2.1 to 2.4 grams of nitrogen, but with a large amount of carbohydrate, some fat and alcohol, that on the fourth day of this “specific nitrogen hunger” only 3 to 4 grams of nitrogen were metabolized and appeared in the urine. In other words, a healthy adult man having a sufficient intake of non-nitrogenous food seemingly need not metabolize more proteid than suffices to yield 3 to 4 grams of nitrogen per day.
Such data as these, of which many more might be quoted, surely warrant the question, how far are we justified in assuming the necessity for the rich proteid diet called for by the Voit standard? Voit, however, with many other physiologists would apparently object to any diminution of the daily 118 grams of proteid for the moderate worker, on the ground that an abundance of proteid in the food is a necessity for the maintenance of physical vigor and muscular activity. This view is certainly reinforced by the customs and habits of mankind; but we may well query whether our dietetic habits will bear criticism, and in the light of modern scientific inquiry we may even express doubt as to whether a rich proteid diet adds anything to our muscular energy or bodily strength.
How far can our natural instinct be trusted in the choice of diet? We are all creatures of habit, and our palates are pleasantly excited by the rich animal foods with their high content of proteid, and we may well question whether our dietetic habits are not based more upon the dictates of our palates than upon scientific reasoning or true physiological needs. There is a prevalent opinion that to be well nourished the body must have a large excess of fat deposited throughout the tissues, and that all bodily ills and weaknesses are to be met and combated by increased intake of food. There is constant temptation to increase the daily ration, and there is almost universal belief in the efficacy of a rich and abundant diet to strengthen the body and to increase bodily and mental vigor. Is there any justification for these beliefs? None, apparently, other than that which comes from the customs of generations of high living.
It is self-evident that the smallest amount of food that will serve to keep the body in a state of high efficiency is physiologically the most economical, and hence the best adapted for the needs of the organism. Any excess over and above what is really needed is not only uneconomical, but may be directly injurious. This is especially true of the proteid or albuminous foods. It is, however, quite proper to question whether a brief experiment of a few days in which nitrogenous equilibrium is perhaps established at the low level of 4 to 5 grams of nitrogen, the equivalent of 25 to 35 grams of proteid, is to be accepted as fixing the daily requirements of the healthy man, offsetting the customs or habits of a lifetime. Voit himself, however, has clearly emphasized the general principle that the smallest amount of proteid, with non-nitrogenous food added, that will suffice to keep the body in a state of continual vigor is the ideal diet. Proteid decomposition products are a constant menace to the well-being of the body; any quantity of proteid or albuminous food beyond the real requirements of the body may prove distinctly injurious. We see the evil effects of uric acid in gout, but there are many other nitrogenous waste products of proteid katabolism, which with excess of proteid food are liable to be unduly conspicuous in the fluids and tissues of the body, and may do more or less damage prior to their excretion through the kidneys. Further, it requires no imagination to understand the constant strain upon the liver and kidneys, to say nothing of possible influence upon the central and peripheral parts of the nervous system, by these nitrogenous waste products which the body ordinarily gets rid of as speedily as possible. They are an ever present evil, but why increase them unnecessarily? This question brings us back to the starting-point. What is the minimal proteid requirement for the healthy man, or rather, how far can we safely and advantageously diminish our proteid intake below the commonly accepted standards?
The question of safety is a pertinent one. Thus, Munk[23] some years ago (1893) sounded a warning on this point which was later confirmed by Rosenheim.[24] Both of these observers reported that in dogs fed for some time on a low proteid diet, but with an abundance of carbohydrate and fat, there was after some weeks (6-8) a loss of the power of absorption from the alimentary tract, dependent not alone upon a changed condition of the epithelial cells of the intestine, but also upon a diminished secretion of the digestive juices, loss of body-weight, strength, and vigor, followed speedily by death. If these results were really due to the low proteid diet, they suggest a grave danger which must not be lightly passed by. Jägerroos[25] has likewise observed, experimenting on dogs, that there was, after some months, a striking disturbance of the intestines on a low proteid intake, which, however, was eventually traced to a distinct infection, and probably in no manner connected with the diminished amount of proteid in the diet. In these various experiments on dogs carried out by Munk, Rosenheim, and by Jägerroos, there was of necessity great monotony in the diet, and in Munk’s experiments no fresh meat at all was fed, but simply dried food. In other words, if the diet was in any sense responsible for the poor health of the animals, it is fully as plausible to attribute the results to the abnormal conditions under which the animals were kept as to any specific effect due to the low proteid intake. It is very essential that the food of dogs, as of men, shall fulfil all ordinary hygienic conditions. It must be not only of sufficient quantity for the true needs of the body, but it should also have the necessary variety with reasonable degree of digestibility, and proper volume or bulk. When these qualities are lacking, it is not strange if deviations from the normal gradually develop. That the low intake of proteid food could be responsible for the condition existing in Munk’s and Rosenheim’s experiments is not plausible; a view which is strongly reinforced by many observations, notably those of Albu[26] on a woman thirty-seven years old and weighing 37.5 kilos, who had followed a vegetarian diet for six years, and who while under Albu’s care for two years consumed only 34 grams of proteid per day, the total fuel value of the food being only 1400 calories per day. This woman was in nitrogenous equilibrium on 5.4 grams of nitrogen, and on this diet had freed herself from the illness to which she had long been subject.
Voit’s[27] vegetarian is described by Voit himself as a man twenty-eight years old, weighing 57 kilos, well nourished, with well developed muscles, etc. He had lived on a purely vegetable diet for three years, and was found to be in nitrogenous equilibrium on 8.2 grams of nitrogen. No mention is made of any disagreeable effects connected with this low proteid ration, although persisted in for several years. Jaffa’s[28] experiments and observations on the fruitarians and nutarians of California “showed in every case (two women and three children) that though the diet had a low protein and energy value, the subjects were apparently in excellent health and had been so during the five to eight years they had been living in this manner.” In comparing the income and outgo of nitrogen on a diet composed mainly of nuts and fruits, it was observed in two subjects that 8 grams of nitrogen were sufficient to bring about nitrogen equilibrium, while with two other subjects on a like diet the nitrogen required daily for equilibrium was about 10 grams. The diet used in these experiments, however, was of necessity more or less restricted in variety, and was without doubt somewhat monotonous. Jaffa appears to agree with Caspari that the minimum amount of proteid required daily varies with the individual, and may even vary with the same individual at different times. Further, Jaffa, in harmony with Siven, believes that after the body has suffered a loss of nitrogen, there is at once an effort to attain nitrogenous equilibrium, and that any gain of nitrogenous body material is a comparatively slow process. If this is true, it is obvious that the living substance of the tissue protoplasm must be slowly formed from the proteid of the diet. This, says Jaffa, should serve as a warning to anyone contemplating any appreciable decrease in the proteid of the daily diet.