Passing down to our own times, we find physiologists, by the aid of scientific methods, studying the effects of smaller amounts of food (smaller than custom prescribes) on the condition of the body, thereby evincing a certain degree of skepticism concerning the dietary standards based on habit and usage. This has been especially true regarding the nitrogen requirement, or the need for proteid food. As has been clearly pointed out in other connections, there are two distinct needs which the body has for food; one for proteid or nitrogen, the other for energy-yielding material. According to the Voit standard, a man of average body-weight doing a moderate amount of work requires daily 118 grams of proteid food, or about 16 grams of metabolizable nitrogen, with fat and carbohydrate sufficient to yield a total fuel value of over 3000 large calories. As we have seen, the fuel value of the food must of necessity be a variable quantity because of variations in bodily activity. The more muscular work performed, the greater must be the intake of carbohydrate and fat, if the body is to be kept in equilibrium. With proteid or nitrogen, however, the case is quite different, since with adequate amounts of non-nitrogenous food, proteid is not drawn upon for the energy of muscular work. We can conceive of the nitrogen requirement, therefore, as being a constant factor in the well-nourished individual and dependent primarily upon body-weight, or more exactly, upon the weight of true proteid-containing tissue. Obviously, whatever else happens, there must be enough proteid food taken daily to maintain the body in nitrogen equilibrium. If this can be accomplished only by the ingestion of 16 grams of metabolizable nitrogen, then it is plain that the daily ration must contain at least 118 grams of proteid food; i. e., it must conform approximately at least to ordinary usage.

This question has been studied by many investigators, with very interesting and suggestive results. Thus, in 1887, Hirschfeld[55] reported some experiments on himself, twenty-four years of age and weighing 73 kilos. His ordinary diet contained daily 100 to 130 grams of proteid, and the amount of nitrogen excreted varied from 16 to 20 grams per day, corresponding to a metabolism of proteid equal to the amount ingested. In other words, the body was essentially in nitrogen equilibrium. Then, for a period of fifteen days, during which he was unusually active, he lived on a diet in which the content of proteid corresponded to only 6 grams of nitrogen per day, and yet he remained in nitrogen equilibrium. The diet made use of was composed essentially of milk, eggs, rice, potatoes, bread, butter, sugar, and coffee, with some wine and beer, and on two days a little meat. It is to be observed that the nitrogen or proteid intake per day was only one-third of what he was accustomed to consume. In a second experiment, covering ten days, similar results were obtained. So that evidence was afforded that a young and vigorous man can maintain his body in nitrogen equilibrium, for fifteen consecutive days at least, on an amount of proteid food equal to only one-third of the minimal requirement called for by common usage. Plainly, the difference between a daily consumption of 118 grams of proteid food and 40 grams represents a large percentage saving, both of proteid and in the metabolism of proteid matter with all the attendant transformations. In these experiments, however, the subject consumed relatively large amounts of non-nitrogenous food, notably butter, of which on some days he took as much as 100 grams. The average fuel value of his food ranged from 3750 to 3916 calories per day; a fact of some importance, since it is to be remembered that both fat and carbohydrate tend to protect proteid metabolism.

In an experiment reported in 1889 by Carl Voit[56], on a vegetarian weighing about 57 kilos, it was found that with a purely vegetable diet the subject was able, for a few days at least, to maintain his body in essentially a condition of nitrogen equilibrium on a daily diet containing 8.4 grams of nitrogen, corresponding to 52.5 grams of proteid. In addition, there was a large consumption of starchy food with some fat. Klemperer,[57] experimenting with two young men, having a body-weight of 64 and 65.5 kilos, respectively, was able to keep them in a condition of nitrogenous equilibrium for a period of eight days on 4.38 grams and 3.58 grams of nitrogen per day. The diet, however, had a large fuel value, 5020 calories per day, and contained in addition to the small amount of proteid, 264 grams of fat, 470 grams of carbohydrate, and 172 grams of alcohol. Breisacher,[58] in an experiment on himself, using a mixed diet composed of 67.8 grams of proteid, 494.2 grams of carbohydrate, and 60.5 grams of fat per day, with a total fuel value of 2866 calories, observed a daily excretion of nitrogen during thirty days of 8.23 grams. This corresponds to a metabolism of 51.4 grams of proteid, thus showing that the 67 grams of food-proteid taken was quite sufficient to maintain nitrogen equilibrium for the above length of time.

Caspari and Glässner[59] have reported observations made on two vegetarians, a man and his wife, aged 49 and 48 years respectively, who had lived for some years exclusively on a vegetable diet. The man had a body-weight of 68.8 kilos, while the woman weighed 58 kilos. During five days, the man consumed per day, on an average, 7.83 grams of nitrogen and 4559 calories. This corresponds to 0.114 gram of nitrogen per kilo of body-weight, and 66 calories per kilo. On this diet, the man gained slightly in weight and showed a plus nitrogen balance of 5.2 grams for the five days. In other words, even this low nitrogen or proteid intake was more than sufficient to meet the wants of his body. The wife, during the same period of time, consumed per day 5.33 grams of nitrogen and 2715 calories, corresponding to 0.092 gram of nitrogen per kilo of body-weight and 47 calories per kilo. On this diet, the woman gained 0.9 kilo in weight during the five days, and like the man, she showed a plus nitrogen balance of 2.45 grams for the entire period. The somewhat noted experiments of Sivén have been referred to in another connection, and it will suffice to recall the fact that he was able, with a body-weight of 60 kilos, to establish nitrogen equilibrium on 6.26 grams of nitrogen, and for a day or two on 4.5 grams of nitrogen, with a total fuel value of only 2444 calories in the day’s ration.

These few illustrations will serve to indicate that, so far as the maintenance of nitrogen equilibrium is concerned during short periods of time, there is no necessity for the consumption of proteid food in such amounts as common usage dictates. The high proteid intake called for by the “standard dietaries,” and the ordinary practices of mankind, is not needed to establish a condition of nitrogen equilibrium. It would seem, however, as if results of this nature, presented from time to time by various investigators, have been considered more in the light of scientific curiosities than as data having an important bearing on physiological processes. So strong has been the hold upon the medical and physiological mind of the necessity of high proteid that such figures as the above have merely excited comment, without weakening in any measure the prevalent conviction that health, strength, and the power to work necessitate a high rate of proteid exchange.

To one willing to accept the data as having possible significance there arises at once the question, How long can the body be maintained in nitrogen equilibrium on such relatively small quantities of proteid food? In other words, can experiments of this nature, extending over comparatively short periods of time, be safely accepted as a reliable means of measuring the proteid requirements of the body for indefinite periods? Suppose, says the critic, we grant that the body can maintain itself in nitrogen equilibrium for a week or two on a very small amount of proteid food, what proof have we that in the long run the body will be benefited thereby, or even able to exist in a condition of normal strength and vigor? In other words, is a low proteid diet, one that seems sufficient to maintain the body in nitrogen equilibrium, a wholly safe one to follow? May there not be other elements to be considered, aside from nitrogen equilibrium, which, if fully understood, would satisfactorily account for the customs of mankind, in which perhaps man’s instincts have been followed for the betterment of the race? It was with a view to learning more concerning these questions that five years ago the writer commenced systematic, experimental, work upon the nutrition of man, with special reference to his nitrogen requirements. The experiments and observations have been continued up to the present time, with many suggestive results, some of which will now be referred to.[60]

One group of subjects was composed of professional men, professors and instructors in the university, whose work was mainly mental rather than physical, though by no means excluding the latter. Of this group, two cases will be referred to with some regard for detail, since in no other way can so striking a picture be presented of the effects produced. The first subject weighed 65 kilos in the fall of 1902, and at that time was nearly 47 years of age. His dietetic habits were in accord with common practice, and his daily consumption of proteid food averaged close to 118 grams. With a clear recognition of the principle that the habits of a lifetime should not be too suddenly changed, a very gradual reduction in the total amount of food, and especially of proteid matter, was made. This finally resulted, with this particular subject, in the complete abolition of breakfast, with the exception of a small cup of coffee. A light lunch was taken at noontime, followed by a more substantial dinner at night. There was no change to a vegetable diet, but naturally any attempt to cut off largely the amount of proteid food necessarily results in a marked diminution in the quantity of animal food or meats. It is a somewhat singular though suggestive fact, that a change of this order gradually results in a stronger liking for simple foods, with their more delicate flavor, accompanied by a diminished desire for the heavier animal foods.

As the day’s ration was gradually reduced in amount, the body-weight began to fall off, until after some months it became stationary at 57 kilos, at which point it has remained practically constant for over three years. The sixteen pounds of weight lost was composed, mainly at least, of superfluous fat. For a period of nine months, from October, 1903, to the end of June, 1904, the amount of proteid material broken down in the body was determined each day. The average daily metabolism of nitrogen for the entire period of nearly nine months amounted to 5.69 grams. For the last two months, it averaged 5.4 grams per day. Analyses made from time to time since these figures were obtained show that the subject is still living at the same low level of nitrogen metabolism. In fact, the data available afford satisfactory proof that for a period covering over three years this particular person has subsisted on an amount of proteid food equal to a metabolism of not more than 5.8 grams of nitrogen per day. It may be asked why the subject should have continued such a low proteid diet after the nine months’ period was completed? In reply, it may be said that the new habit has taken a firm hold, and entirely supplanted the dietetic desires and cravings of the preceding years. Further, the improved condition of health, freedom from minor ailments that formerly caused inconvenience and discomfort, and the greater ability to work without fatigue, have all combined to place the new habit on a firm basis, from which there is no desire to change.

Consider for a moment what this lowered consumption of proteid food really amounts to, as compared with ordinary usage and the so-called dietary standards. The latter call for at least 118 grams of proteid or albuminous food daily, of which 105 grams should be absorbable, in order to maintain the body in a condition of nitrogen equilibrium, and in a state of physical vigor and general tone. This would mean a daily metabolism and excretion of at least 16 grams of nitrogen. Our subject, however, excreted per day, during nine months, only 5.69 grams of nitrogen, which means a metabolism of 35.6 grams of proteid; i. e., about one-third the amount ordinarily deemed necessary to meet man’s requirement for proteid food. But was our subject in nitrogen equilibrium on this small amount of proteid food? We answer yes, as the following balance period shows:

Output.

Nitrogen in
Food.

Nitrogen through
Kidneys.

Weight of Excre-
ment (dry).

March 20

 6.989 grams. 5.91 grams. 3.6 grams.

21

 6.621 5.52 . .

22

 6.082 5.9412.0

23

 6.793 5.6118.5

24

 5.057 4.3123.0

25

 6.966 5.3916.9
──── ──────
74.0 grams contain
  6.42% N.
38.50832.68  +4.75 grams nitrogen.
──────────────────
38.508 grams nitrogen. 37.43 grams nitrogen.

Nitrogen balance for six days  =  +1.078 grams.

Nitrogen balance per day     =  +0.179 gram.