The nutrition of man

FURTHER EXPERIMENTS AND OBSERVATIONS BEARING ON TRUE FOOD REQUIREMENTS

Topics: Dietary experiments with a detail of soldiers from the United States army. General character of the army ration. Samples of the daily dietary adopted. Rate of nitrogen metabolism attained. Effect on body-weight. Nitrogen balance with lowered proteid consumption. Influence of low proteid on muscular strength of soldiers and athletes. Effect on fatigue. Effect on physical endurance. Fisher’s experiments on endurance. Dangers of underfeeding. Dietary observations on fruitarians. Observations on Japanese. Recent dietary changes in Japanese army and navy. Observations of Dr. Hunt on resistance of low proteid animals to poisons. Conclusions.

General acceptance of a new theory, or a new point of view, can be expected only when there is an adequate amount of scientific evidence on which the theory can safely rest. Facts cannot be ignored, and the larger the amount of supporting evidence the more certain becomes the general truth of the theory to which it points. Corroborative evidence, therefore, is always desirable, and he who would open up a new point of view must be zealous in accumulating facts to uphold his position. Critics there are without number who are ever ready to pick flaws in an argument or overturn a theory, especially if the one or the other stands opposed to their own point of view. This, however, is highly advantageous for the advance of sound knowledge, since it necessarily prompts the advocate to search in all directions for added data, by which he can build a bulwark of fact sufficient to defy just criticism. Further, the true scientific spirit demands persistent and painstaking effort in the search after truth, that error and misconception may be avoided.

In harmony with these ideas, our attempt to ascertain the real needs of the body for proteid food led us to enlarge our evidence by a series of experiments with still another body of men, i. e., a detail of soldiers from the United States army.61 This was a somewhat more difficult and ambitious undertaking, since the number of subjects involved was larger, and because with this group of men we could not expect quite that high degree of intelligent co-operation afforded by the preceding subjects. Still, this very fact was in a sense an added inducement, since it offered the opportunity of experimenting with a body of men who naturally would not take kindly to anything that looked like deprivation, and whose continued co-operation could be expected only by satisfying their natural demands for food. If this could be accomplished by an intelligent prescription in their daily diet, and the experiment brought to a successful conclusion, with maintenance of body-weight, nitrogen equilibrium, health, strength, and general vigor; with an intake of proteid food essentially equal to that adopted by the preceding subjects, corroborative evidence of the highest value would be obtained.

The detail was composed of a detachment of twenty men from the Hospital Corps of the army, under the command of a first lieutenant and assistant surgeon. They were located in a convenient house near to the laboratory, where they lived during their six months’ stay in New Haven, under military discipline, and subject to the constant surveillance of the commanding officer and the non-commissioned officers. Having well-trained cooks and assistants, with all necessary facilities for preparing and serving their food, with members of the laboratory staff to superintend the weighing of the food as it was placed before the men, and with intelligent clerks to attend to the many details connected with such an undertaking, a somewhat unique physiological experiment was started. Thirteen members of the detachment really took part in the experiment as subjects, and they represented a great variety of types: of different ages, nationalities, temperaments, and degrees of intelligence. They were men accustomed to living an active life under varying conditions, and they naturally had great liking for the pleasures of eating. Further, it should be remembered that, although the men had volunteered for the experiment, they had no personal interest whatever in the principles involved, and it could not be expected that they would willingly incommode themselves, or suffer any great amount of personal inconvenience. Again, there were necessary restrictions placed upon their movements, when relieved from duty, which constituted something of a hardship in the minds of many of the men and added to the irksomeness and monotony of their daily life. Regularity of life was insisted upon, and this was a condition which brought to some of the men a new experience. These facts are mentioned because their recital will help to make clear that, from the standpoint of the men, there were certain depressing influences connected with the experiment which would add to any personal discomfort caused by restriction of diet.

The ordinary army ration to which these men were accustomed was rich in proteid, especially in meat, and during the first few days they were allowed to follow their usual dietary habits, in order that data might be obtained bearing on their average food consumption. The details of one day’s food intake will suffice to show the average character and amount of the food eaten per man:

It is not necessary to comment upon the large proportion of proteid matter in the day’s ration; the three large portions of meat testify clearly enough to that fact, while the three equally large volumes of coffee indicate a natural disposition toward generous consumption of anything available. Habit, reinforced by inclination, had evidently placed these men on a high plane of food consumption.

For a period of six months, a daily dietary was prescribed for the subjects; the food for each meal and for every man being of known composition, each article being carefully weighed, while the content of nitrogen in the day’s ration was so graded as to bring about a gradual reduction in the amount of proteid ingested. The rate of proteid katabolism was likewise determined each day by careful estimation of the excreted nitrogen, balance experiments being made from time to time in order to ascertain if the men were in a condition of nitrogen equilibrium. Finally, it should be mentioned that the subjects lived a fairly active life, having each day a certain amount of prescribed exercise in the university gymnasium, in addition to the regular drill and other duties associated with their usual work.

As just stated, the amount of proteid food was gradually reduced, three weeks being taken to bring the amount down to a level somewhat commensurate with the estimated needs of the body. This naturally resulted in diminishing largely the intake of meat, though by no means entirely excluding it. Effort was constantly made to introduce as much variety as was possible with simple foods, though the main problem with this group of men was to keep the volume of the food up to such a point as would dispel any notion that they were not having enough to eat. A second problem, which at first threatened trouble, was the fear of the men, as they saw the proportion of meat gradually drop off, that they were destined to lose their strength; but fortunately, they very soon began to realize that their fears in this direction were groundless, and a little later their personal experience opened their eyes to possible advantages which quickly drove away all further thought of danger, and made them quite content to continue the experiment. We may introduce here a few samples of the daily food given to the men after they had reached their lower level of proteid intake:

January 15.

January 16.

March 1.

March 3.

March 6.

March 30.

March 31.

April 1.

These dietaries are fair samples of the daily food given the men during the last five months of the experiment. If we place the intake of nitrogen at 8.5 grams per day, or even 9 grams daily, it would mean at the most an average daily consumption of 56 grams of proteid; viz., about one-third the amount they were accustomed to take under their ordinary modes of life. Of greater interest, however, is the rate of proteid katabolism shown by these men under the above conditions of diet, during the five months’ period. The average daily output of metabolized nitrogen for each man ranged from 7.03 grams—the lowest—to 8.91 grams—the highest. An excretion of 7.03 grams of nitrogen per day means a katabolism, or breaking down, of 43.9 grams of proteid matter; while the excretion of 8.91 grams of nitrogen corresponds to a katabolism of 55.6 grams of proteid. The grand average, i. e., the average daily output of nitrogen of all the men for the five months’ period amounted to 7.8 grams per man, corresponding to an average daily katabolism of 48.75 grams of proteid. The heaviest man of the group had a body-weight of 74 kilograms, while his average daily output of metabolized nitrogen amounted to 7.84 grams. This corresponds to 0.106 gram of metabolized nitrogen per kilo of body-weight; a figure which agrees quite closely with the lowest figures obtained with the preceding subjects when calculated to the same unit of weight. Many of the men, however, metabolized considerably more nitrogen or proteid in proportion to their body-weight, due in a measure at least to the fact that they were being fed more liberally with proteid food than was really necessary for the needs of the body. In this group, we have a body of men doing a reasonable amount of physical work, who lived without discomfort for five consecutive months on a daily consumption of proteid food not much, if any, greater than one-third the amount called for by common usage, and the average fuel value of which certainly did not exceed 3000 calories per day. Indeed, so far as could be determined on the basis of chemical composition, the heat value of the food was quite a little less than this figure would imply.

If the relatively small amount of proteid food made use of in this trial was inadequate for the real necessities of the body, some indication of it would be expected to reveal itself, with at least some of the men, by the end of the period. One criticism frequently made is that the subject draws in some measure upon his store of body material. Should this be the case, it is evident that body-weight—in such a long experiment as this—will gradually but surely diminish. Further, the subject will show a minus nitrogen balance, i. e., there will be a constant tendency for the body to give off more nitrogen than it takes in. As bearing on the first point, the following table showing the body-weights of the men at the commencement of the experiment in October, and at the close of the experiment in April will be of interest:

As is readily seen, five of the men practically retained their weight or made a slight gain. Of the others, Coffman, Loewenthal, Sliney, and Cohn lost somewhat, but the amount was very small. Further, the loss occurred during the first few weeks of the experiment, after which their weight remained practically stationary. Fritz and Oakman lost weight somewhat more noticeably, but this loss likewise occurred during the earlier part of the trial. The accompanying photographs of Fritz, taken at the close of the experiment, show plainly that such loss of weight as he suffered did not detract from the appearance of his well-developed musculature. Certainly, the photographs do not show any signs of nitrogen starvation, or suggest the lack of any kind of food.

Of all the men, Bates was the only one who underwent any great loss of weight. He, however, was quite stout, and the work in the gymnasium, reinforced by the change in diet, brought about what was for him a very desirable loss of body-weight. It is evident, therefore, that there was no marked or prolonged loss of body-weight as a result of the continued use of the low proteid diet. Regarding the second point, viz., nitrogen equilibrium, the following illustrations will suffice to indicate the relationship existing between the income and outgo of nitrogen. A balance experiment with each of the men, lasting seven days, February 29 to March 6, is here shown, the figures given being the daily averages for the period:

With one exception, all of the men were plainly having more proteid food than was necessary to maintain the body in nitrogen equilibrium, the plus nitrogen balance in most cases being fairly large. It is only necessary to remember that a gain to the body of 1 gram of nitrogen means a laying by of 6.25 grams of proteid, and with such a gain per day it is apparent that the men were really being supplied with an excess of proteid food. This view is supported by the fact that a later balance experiment, when considerably less proteid food was being given, still showed many of the men in a condition of plus balance, or with a minus balance so small as to indicate essentially nitrogen equilibrium. The following figures, being daily averages of a balance period about the first of April, may be offered in evidence:

A daily intake of 8.5 grams of nitrogen means the consumption of 53 grams of proteid. Under these conditions of diet, the average daily amount of nitrogen metabolized was 6.45 grams, corresponding to 40.3 grams of proteid. The men were practically in a condition of nitrogen equilibrium, so that we are apparently justified in the general statement that the simple dietary followed with these men during the six months’ experiment, and which was accompanied by an average daily metabolism, after the first three weeks, of 7.8 grams of nitrogen, was certainly sufficient to maintain both body-weight and nitrogen equilibrium. Lastly, emphasis may be laid upon the fact that these values for nitrogen do not necessarily represent the minimal proteid requirement of the human body, since it is a well-established physiological principle that by increase of non-nitrogenous food the rate of proteid katabolism can always be further diminished; a principle which is plainly in harmony with the view that a high rate of proteid exchange is not a necessary requisite for the welfare of the body.

The experimental results presented afford very convincing proof that so far as body-weight and nitrogen equilibrium are concerned, the needs of the body are fully met by a consumption of proteid food far below the fixed dietary standards, and still further below the amounts called for by the recorded habits of mankind. General health is equally well maintained, and with suggestions of improvement that are frequently so marked as to challenge attention. Most conspicuous, however, though something that was entirely unlooked for, was the effect observed on the muscular strength of the various subjects. When the experiments were planned, it was deemed important to arrange for careful quantitative tests of the more conspicuous muscles of the body, with a view to measuring any loss of strength that might occur from the proposed reduction in proteid food. The thought that prompted this action was a result of the latent feeling that somehow muscular strength must be dependent more or less upon the proteid constituents of the muscles, and that consequently the cutting down of proteid food would inevitably be felt in some degree. The most that could be hoped for was that muscle tone and muscular strength might be maintained unimpaired. Hence, we were at first quite astonished at what was actually observed.

With the soldier detail, fifteen distinct strength tests were made with each man during the six months’ period, by means of appropriate dynamometer tests applied to the muscles of the back, legs, chest, upper arms, and forearms, reinforced by quarter-mile run, vault, and ladder tests, etc. The so-called “total strength” of the man was computed by multiplying the weight of the body by the number of times the subject was able to push up (strength of triceps muscles) and pull up (strength of biceps muscles) his body while upon the parallel bars, to this product being added the strength (dynamometer tests) of hands, legs, back, and chest. It should be added that all of these tests were made quite independently in the university gymnasium by the medical assistants and others in charge of the work there. It will suffice for our purpose to give here the strength tests of the various members of the soldier detail at the beginning and close of the experiment.

Without exception, we note with all of the men a phenomenal gain in strength, which demands explanation. Was it all due to the change in diet? Probably not, for these men at the beginning of the experiment were untrained, and it is not to be assumed that months of practical work in the gymnasium would not result in a certain amount of physical development, with corresponding gain in muscular skill and power. Putting this question aside for the moment, however, it is surely proper to emphasize this fact; viz., that although the men for a period of five months were restricted to a daily diet containing only one-third to one-half the amount of proteid food they had been accustomed to, there was no loss of physical strength; no indication of any physical deterioration that could be detected. In other words, the men were certainly not being weakened by the lowered intake of proteid food. This is in harmony with the principle, already discussed, that the energy of muscle work comes primarily from the breaking down of non-nitrogenous material, and consequently a diminished intake of proteid food can have no inhibitory effect, provided, of course, there is an adequate amount of proteid ingested to satisfy the endogenous requirements of the tissues.

On the other hand, recalling the large number of nitrogenous cleavage products which result from the breaking down of proteid material, we can conceive of an exaggerated exogenous proteid katabolism which may flood the tissues and the surrounding lymph with a variety of nitrogenous waste products, having an inhibitory effect upon the muscle fibres themselves, or upon the peripheral endings of the motor nerves, by which the muscles are prevented, directly or indirectly, from working at their highest degree of efficiency. This being true, a reduction of the exogenous katabolism to a level more nearly commensurate with the real needs of the body might result in a marked increase in the functional power of the tissue. However this may be, the fact remains that all of the subjects showed this great gain in strength; and furthermore, there was a noticeable gain in self-reliance and courage in their athletic work, both of which are likewise indicative of an improved condition of the body. How far these improvements are attributable to training and to the more regular life the men were leading, and how far to the change in diet, cannot be definitely determined. We may venture the opinion, however, for reasons to be made clear shortly, that the change in diet was in a measure at least responsible for the increased efficiency. As the writer has already expressed it, there must be enough food to make good the daily waste of tissue, enough food to furnish the energy of muscular contraction, but any surplus over and above what is necessary to supply these needs is not only a waste, but may prove an incubus, retarding the smooth working of the machinery and detracting from the power of the organism to do its best work.

Let us now turn our attention for a moment to the group of university athletes, remembering that these men had been in training for many months, and some of them for several years, prior to the commencement of the trial with a reduced proteid intake. In the words of the director of the gymnasium, “These eight men were in constant practice and in the pink of condition; they were in ‘training form’ when they began the changed diet.” Some of them had gained marked distinction for their athletic work; one during the early months of the test won the Collegiate and All-around Inter-collegiate Championship of America. Compare now the strength tests of these men as taken at the beginning and end of the five months’ experiment, during which they reduced their daily intake of proteid food more than fifty per cent:

It is to be observed that the majority of these trained men showed at the first trial in January a total strength test approximately equal to that of the soldier detail at the close of their experiment. This by no means implies that the latter men owed their gain in strength wholly to the systematic training they had undergone, but it is certainly plausible to assume that in a measure this was the case. In any event, it is plain that the long-continued low proteid diet of the soldiers had not interfered with a progressive muscular development, and the attainment of a high degree of muscular strength.

The noticeable feature in the figures obtained with the athletes, however, is the striking difference between the January and June results. Every man, without exception, showed a decided gain in his muscular power as measured by the strength tests. This improvement, to be sure, was not so marked as with the soldiers; a fact to be expected, since with these men the element of training and the acquisition of proficiency in athletic work could have played no part in the observed gain. Further, most of the tests indicated that the gain was progressive, each month showing an improvement, in harmony with the growing effect of the diminished proteid intake. With these subjects, the only tangible change in their mode of life which could in any sense be considered as responsible for their gain in strength was the change in diet. Consequently, it seems perfectly justifiable to conclude that the observations presented afford reasonable proof of the beneficial effects of a lowered proteid intake upon the muscular strength of man.

The significance of such a conclusion is manifestly obvious. It confirms and gives added force to the observations that man can profitably maintain nitrogen equilibrium, and body-weight, upon a much smaller amount of proteid food than he is accustomed to consume. It harmonizes with the view that the normal requirements of the body for food, under which health, strength, and maximum efficiency are best maintained, are on a far lower level than the ordinary practices of mankind would lead one to believe. The widespread opinion that a rich proteid diet, with the correspondingly high rate of proteid metabolism, is a necessity for the preservation of bodily strength and vigor, is seen to be without foundation; for even the most conservative estimate of the real value of these strength tests must carry with it the conviction that lowering the consumption of proteid food does not at least result in any weakening of the body. This is a fact of vital importance, for it needs no argument to convince even the most optimistic that while it might be possible to maintain body-weight and nitrogen equilibrium on a small amount of proteid food, such a form of physiological economy would not only be of no advantage to the individual, but would be positively injurious if there was a gradual weakening of the muscles of the body with decrease of physical strength, vigor, and endurance.

Another fact to be emphasized in this connection was the conviction, gradually acquired by many of the subjects, that they suffered less from fatigue after vigorous muscular effort than formerly. This was especially conspicuous in the case of Donahue, whose work on the Varsity basket-ball team called for vigorous exercise. It is interesting to note that this athlete, of 63 kilos body-weight, for the last four months of the experiment showed an average daily katabolism of 7.45 grams of nitrogen, corresponding to a breaking down of 46.5 grams of proteid material daily. Yet, with this low rate of proteid exchange, he maintained his position on the team with satisfaction to all, and with the consciousness of improved physical condition and greater freedom from fatigue. Other subjects, as the laboratory workers of the professional group, observed that the customary late afternoon fatigue, coincident with the continued walking and standing about the laboratory, gradually became far less conspicuous than usual; so that there seemed to be a consensus of opinion that in some way the change in diet was conducive to greater freedom from muscular weariness.

It is well understood by physiologists that the ability of a muscle to do work is inhibited by any condition that tends to depress the general nutritive state of the body, or that interferes with the local nutrition of the muscle or muscles involved. On the other hand, there are certain well-recognized conditions that tend to augment the power of the muscle, notably an increased circulation of blood through the tissue, the taking of food, and especially the introduction of sugar. Further, experiments have shown that when a given set of muscles has been made to work excessively, other muscles of the body quite remote will share in the fatigue, thus implying that muscular weariness and the diminished power to do work are connected with what may be termed fatigue products, which are distributed by means of the circulation. In this way, muscles and nerve endings alike are exposed to the inhibitory influence of waste products of unknown composition, formed in the muscle, and as previously stated, we may conceive of an exaggerated exogenous katabolism, with excessive proteid intake, by which muscular fatigue and weariness may be augmented; hence, the beneficial effect in this direction of a more rational food consumption, by which proteid katabolism shall be reduced to a true physiological level.

With these marked effects on strength and fatigue, it is reasonable to assume that some corresponding action may be exerted on physical endurance. As is well known, strength and endurance, though related, are quite distinct and can be separately measured. Strength tests, however, as usually carried out in gymnasium work, do involve in considerable degree the question of endurance, since it is customary to use as one of the factors in estimating total strength the number of times the man can pull up, or push up, his body on the parallel bars. Strictly speaking, however, the strength of a muscle is measured by the maximum force it can exert in a single contraction, while its endurance is estimated from the number of times it can contract well within the limit of its strength.

It is well known that endurance, both physical and mental, is one of the most variable of the human faculties, and it is usually considered that exercise or training is the chief cause of the differences so frequently seen. The Maine guide will row a boat or paddle a canoe for the entire day without undue fatigue, while the novice, though he may have the necessary strength, lacks the endurance to continue the task longer than a few hours. As expressed by Professor Fisher, “Some persons are tired by climbing a flight of stairs, whereas the Swiss guides, throughout the summer season, day after day spend the entire time in climbing the Matterhorn and other peaks; some persons are ‘winded’ by running a block for a street car, whereas a Chinese coolie will run for hours on end; in mental work, some persons are unable to apply themselves more than an hour at a time, whereas others, like Humboldt, can work almost continuously through eighteen hours of the day.” Again, Fisher states that “among some 75 tests of different persons holding their arms horizontal, many were found whose arms actually dropped against their will inside of 10 minutes, whereas several were able to hold them up over 1 hour, and one man held them 3 hours and 20 minutes, or a round 200 minutes, and then dropped them voluntarily. Similarly with deep knee-bending, some persons were found physically unable to rise again from the stooping posture after accomplishing less than 500 bendings, whereas several succeeded in stooping 1000 times, and in one case, 2400.” Here, we have inherent differences in endurance not associated with training or exercise, and the question may well be asked, What is the cause of these radical variations in the ability to repeat a simple muscular exertion?

Hitherto, little attention has been paid to the possible influence of diet upon this faculty. It has always been assumed that endurance, like physical strength, is augmented by a rich proteid diet, but it has never been considered that diet by itself was a factor of any great moment as compared with training or persistent exercise. It is true that claims have been advanced from time to time concerning the beneficial effects on endurance of a vegetable diet, and vegetarians have frequently presented glowing reports of the great increase in endurance they have experienced, but little attention has been given to such statements, and the matter has remained more or less in obscurity.

Recently, Professor Irving Fisher,63 of Yale, has conducted an interesting experiment on the influence of a change in diet on endurance, having the co-operation of nine healthy students as subjects. The experiment extended through five months, with endurance tests at the beginning, middle, and end of the period. At the outset, the men consumed daily an average of 2830 calories, of which 210 were in the form of flesh foods, such as meats, poultry, fish and shell-fish; 2.6 calories of proteid being ingested for each pound of body-weight. At the close of the experiment, the per capita calories had fallen to 2220, of which only 30 were in flesh foods, and the proteid had fallen to 1.4 calories per pound of body-weight. In other words, the total calories of the daily ration had dropped off about 25 per cent, the proteid about 40 per cent, and the flesh foods over 80 per cent, or to about one-sixth of their original amount.

To determine the endurance of the subjects, six simple gymnastic tests were employed, and one of mental endurance. The physical tests consisted of (1) in rising on the toes as often as possible; (2) deep knee-bending, or stooping as far as possible and rising to the standing posture, repeating as often as possible; (3) while lying on the back, raising the legs from the floor to a vertical position and lowering them again, repeating to the point of physical exhaustion; (4) raising a 5-lb. dumb-bell (with the triceps) in each hand from the shoulder up to the highest point above the head, repeating to the point of physical exhaustion; (5) holding the arms from the sides horizontally for as long a time as possible; (6) raising a dumb-bell (with the biceps) in one hand from a position in which the arm hangs free, to the shoulder and back, repeating to the point of physical exhaustion. This test was taken with four successive dumb-bells of decreasing weight, viz., 50, 25, 10, and 5 pounds respectively. The mental test consisted in adding specified columns of figures as rapidly as possible, the object being to find out whether the rapidity of performing such work tended to improve during the experiment.

The following table shows the results of the three sets of physical tests made in January, March, and June: