PHYSIOLOGICAL ECONOMYIN NUTRITIONINTRODUCTORYNote.—For the benefit of lay readers,metabolism, a word frequently made use of, may be defined as a term applied to the collective chemical changes taking place in living matter. When these metabolic changes are constructive, as in the building up of tissue protoplasm from the absorbed food material, they are termedanabolic; when they are destructive, as in the breaking down of living matter or in the decomposition of the materials stored up in the tissues and organs, they are termedkatabolic. Proteid metabolism, or more exactly proteid katabolism, therefore, means the destructive decomposition of proteid or albuminous matter in the living body and is practically synonymous with nitrogenous metabolism, since the entire nitrogen income is mainly supplied by the proteids or albuminous matters of the food. The chief carbon income, on the other hand, is supplied by fats and carbohydrates, such as starches and sugars.
Note.—For the benefit of lay readers,metabolism, a word frequently made use of, may be defined as a term applied to the collective chemical changes taking place in living matter. When these metabolic changes are constructive, as in the building up of tissue protoplasm from the absorbed food material, they are termedanabolic; when they are destructive, as in the breaking down of living matter or in the decomposition of the materials stored up in the tissues and organs, they are termedkatabolic. Proteid metabolism, or more exactly proteid katabolism, therefore, means the destructive decomposition of proteid or albuminous matter in the living body and is practically synonymous with nitrogenous metabolism, since the entire nitrogen income is mainly supplied by the proteids or albuminous matters of the food. The chief carbon income, on the other hand, is supplied by fats and carbohydrates, such as starches and sugars.
As the result of many years of observation and experiment certain general conclusions have been arrived at regarding the requisite amounts of food necessary for the maintenance of health and strength. Certain dietary standards have been set up which have found more or less general acceptance in most parts of the civilized world; standards which have been reinforced and added to by man’s aptitude for self-indulgence. Carl Voit, of Munich, whose long and successful life as a student of Nutrition renders his conclusions of great value, considers that an adult man of average body-weight (70-75 kilos) doing moderate muscular work requires daily 118 grams of proteid or albuminous food, of which 105 grams should be absorbable, 56 grams of fat, and 500 grams of carbohydrate, with a total fuel value of over 3000 large calories, in order to maintain the body in equilibrium. The Voit standard or daily diet is accepted more or less generally as representing the needs of the body under normal conditions of life, andthe conclusions arrived at by other investigators along these same lines have been more or less in accord with Voit’s figures. In confirmation of this statement the following data may be quoted:
AVERAGE DIETS.
In many of these diets it is to be noted that the proteid requirement is placed at even a higher figure than Voit’s standard. Similarly, Erisman, studying the diets of Russian workmen having a free choice of food and doing moderately hard work, found the daily diet to be composed of 131.8 grams of proteid, 79.7 grams of fat, and 583.8 grams of carbohydrate, with a total fuel value of 3675 large calories. Further, Hultgren and Landergren[6]found that Swedish laborers doing hard work had as their daily diet 189 grams of proteid, 110 grams of fat, and 714 grams of carbohydrate, with a total fuel value of 4726 large calories. Voit found that German soldiers on active service consumed daily 145 grams of proteid, 100 grams of fat, and 500 grams of carbohydrate, with a total fuel valueof 3574 large calories. Lichtenfelt,[7]studying the nutrition of Italians, states that an Italian laborer doing a moderate amount of work requires 110.5 grams of proteid and a total fuel value for the daily food of 2698 calories, while at hard labor he needs 146 grams of proteid daily, with carbohydrates and fat sufficient to give 3088 large calories. In our own country Atwater,[8]who has made many valuable observations upon the dietetic habits of different classes of people and under different conditions of life, has stated that a somewhat more liberal allowance of proteid would seem desirable, say 125 grams, with a total fuel value of 3500 large calories for a man doing severe muscular labor.
In what is perhaps the latest book on alimentation, Armand Gautier,[9]writing of the French people, states that the ordinary man in that climate needs daily 110 grams of albuminous food, 68 grams of fat, and about 423 grams of amylaceous or saccharine food. It is possible, however, says Gautier, that the quantity of albuminous food can be reduced, if necessary, to 78 grams per day in case a man is not doing work and takes in addition at least 50 grams of fat and 485 grams of carbohydrate food. Where, however, an individual works eight to ten hours a day, the ration, says Gautier, must be increased to at least 135 grams of albuminous food, with 85 to 100 grams of fat, and with from 500 to 900 grams of starchy food.
While these figures may be taken as showing quite conclusively the dietetic standards adopted by mankind, there is no evidence whatever that they represent the real needs or requirements of the body. We may even question whether simple observation of the kinds and amounts of food consumed by different classes of people under different conditions of life have any very important bearing upon this question. Theythrow light upon dietetic habits, it is true, but such observations give no information as to how far the diets in question serve the real needs of the body. We may find, for example, that under certain given conditions of diet the people in question have the appearance of being well nourished, and that they do their work with apparent ease and comfort; but might not these same results follow with smaller amounts of food? If so, there must of necessity be a certain amount of physiological economy under the more restricted diet, and a consequent ultimate gain to the body through diminished wear and tear of the bodily machinery.
Indeed, experimental work and observations scattered through the last few years have suggested the possibility of much lower standards of diet sufficing to meet the real physiological needs of the body. Thus, Hirschfeld,[10]in 1887, found in experimenting on himself (24 years of age and weighing 73 kilos) that it was possible to maintain nitrogen equilibrium on a diet containing only 5 to 7.5 grams of nitrogen per day, or 35 to 45 grams of proteid, for a period of ten to fifteen days. The amount of non-nitrogenous food consumed, however, was fairly large, especially the amount of butter,—frequently 100 grams a day—the average fuel value ranging from 3750 to 3916 large calories daily. In 1888 Hirschfeld,[11]again experimenting on himself, maintained nitrogen equilibrium for several days on 7.5 grams of nitrogen per day, with fats and carbohydrate sufficient to yield a total fuel value of 3462 large calories as the daily average. The chief criticism of Hirschfeld’s experiments is that he failed to obtain in all cases definite analytical data of the food-stuffs employed and failed to determine the nitrogen of the fæces. Still his results are of value as indicating the possibility of maintaining nitrogenous equilibrium for a brief time at least on a low proteid intake.
Kumagawa,[12]studying especially the diet of the Japanese and experimenting on himself (27 years old and weighing 48 kilos), found with a purely vegetable diet, containing per day 54.7 grams of proteid, 2.5 grams of fat, and 569.8 grams of carbohydrate, that he showed for a period of nine days a plus balance of nitrogen, indicating that his body was laying on about 4 grams of proteid per day. The nitrogen excreted per urine and fæces amounted to 8.09 grams per day, while the nitrogen in the daily food amounted to 8.75 grams. It is interesting to observe in these experiments, as indicating the degree of absorption of the vegetable food (composed in large measure of rice) that the daily average of nitrogen in the urine amounted to 6.069 grams and in the fæces 2.029 grams. In other words, of the 54.7 grams of nitrogen-containing food only 37.8 grams were absorbed, 12.69 grams passing out with the fæces. The total fuel value of the absorbed food per day was 2478 large calories. Similarly, Hirschfeld[13]has called attention to the fact that with many vegetable foods especially, not more than 75 per cent of the ingested proteid can be digested and absorbed, thus emphasizing the necessity of paying heed to thecharacterof the proteid food in considering the nutritive value of a given diet.
In some experiments reported by C. Voit[14]in 1889, on the diet of vegetarians, E. Voit and Constantinidi found that nitrogenous equilibrium was established in one man with about 8 grams of nitrogen, corresponding to 48.5 grams of proteid as the daily diet, with large amounts of starchy foods and some fat. Similarly, Nakahama[15]in the same year, studying the diet (mostly vegetable) and nutritive condition of thirteen German laborers in Leipzig, found that their dailyfood contained on an average 85 grams of proteid, but Carl Voit criticising these results states that the men were of comparatively light body-weight—about 60 kilos—and not well nourished.
Kellner and Mori,[16]studying the nutrition of a Japanese (weighing 52 kilos and 23 years of age) state that on a purely vegetable diet containing 11.34 grams of nitrogen, of which only 8.58 grams were digested, there was a distinct loss of body-weight, with a daily loss to the body of 1.16 grams of nitrogen. On a mixed diet, however, containing fish, it was possible to establish nitrogenous equilibrium with a daily diet containing 17.48 grams of nitrogen, of which 15.27 grams were digested and utilized. Similarly, Caspari,[17]29 years old and weighing 66.2 kilos, found that while he could maintain his body in nitrogenous equilibrium on 13.26 grams of nitrogen per day, he could not accomplish it on 10.1 grams of nitrogen, though his daily food contained 3200 large calories.
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 abrief 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 physiologistswould 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. Ifthese 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 beslowlyformed 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.
Another statement made by Jaffa may be quoted in thisconnection, since it illustrates the attitude taken by many physiologists on this question. “Even if it could be proved,” says Jaffa, “by a large number of experiments that nitrogen equilibrium can be maintained on a small amount of protein, it would still be a great question whether or not it would be wise to do so. There must certainly be a constant effort on the part of the human organism to attain this condition, and with a low protein supply it might be forced to do so under conditions of strain. In such a case the bad results might be slow in manifesting themselves, but might also be serious and lasting. It has also been suggested that when living at a fairly high protein level the body is more resistant to disease and other strains than when the protein level is low.” While these suggestions demand careful consideration, it is equally evident that there is another side to the question, viz., the possible danger to the body from the physiological action of the larger amounts of nitrogenous waste products which result from an excess of proteid food, and which float about through the system prior to their excretion. In addition, we must not overlook the great loss of energy to the body in handling and getting rid of the surplus of unnecessary food of whatever kind introduced into the alimentary tract, to say nothing of the danger of intestinal putrefaction and toxæmia when from any cause the system loses its ability to digest and absorb the excess of food consumed. Further, the possible strain on the kidneys and other organs must not be overlooked. Hence we may well query on which side lies the greater danger. To an unprejudiced observer, one not wedded to old-time tradition, it would seem as if great effort was being made to sustain the claims of a high-proteid intake. It is surely well to be careful, but it is certainly not necessary to magnify imaginary dangers to the extent of suppressing all efforts toward the establishment of possible physiological economy.
In a paper read before the Physiological Section of the British Medical Association in 1901 by Dr. van Someren, claim is made of the existence of a reflex of deglutition, the proper working of which protects from the results of malnutritionby preventing the intake of any excess of food. Thorough mastication and insalivation aid in the more complete utilization of the food and render possible great economy, so that body-weight and nitrogen equilibrium are both maintained on an exceptionally small amount of food. This principle had been worked out by Mr. Horace Fletcher on himself in an attempt to restore his health to a normal condition, with such beneficial results that he was speedily restored to a state of exceptional vigor and well-being. Deliberation in eating, necessitated by the habit of thorough insalivation, it is claimed results in the occurrence of satiety on the ingestion of comparatively small amounts of food, and hence all excess of food is avoided.
In the autumn of 1901, Mr. Fletcher and Dr. van Someren visited the physiological laboratories of Cambridge University, and as stated by Sir Michael Foster[29]the matter was more closely inquired into with the assistance of physiological experts. Observations were carried out on various individuals, and as stated by Professor Foster “the adoption of the habit of thorough insalivation of the food was found in a consensus of opinion to have an immediate and very striking effect upon appetite, making this more discriminating, and leading to the choice of a simple dietary, and in particular reducing the craving for flesh food. The appetite, too, is beyond all question fully satisfied with a dietary considerably less in amount than with ordinary habits is demanded.”... “In two individuals who pushed the method to its limits it was found that complete bodily efficiency was maintained for some weeks upon a dietary which had a total energy value of less than one-half of that usually taken, and comprised little more than one-third of the proteid consumed by the average man.” Finally, says Foster, “it may be doubted if continued efficiency could be maintained with such low values as these, and very prolonged observations would be necessary to establish the facts. But all subjects of the experiments who applied the principlesintelligently agreed in finding a very marked reduction in their needs, and experienced an increase in their sense of well-being and an increase in their working powers.”
In the autumn of 1902 and in the early part of 1903, Mr. Fletcher spent several months with the writer, thereby giving an opportunity for studying his habits of life. For a period of thirteen days in January he was under constant observation in the writer’s laboratory, when it was found that the average daily amount of proteid metabolised was 41.25 grams, his body-weight (75 kilos) remaining practically constant. Later, a more thorough series of observations was made, involving a careful analysis of the daily diet, together with analysis of the excreta. For a period of six days the daily diet averaged 44.9 grams of proteid, 38.0 grams of fat, and 253 grams of carbohydrate, the total fuel value amounting to only 1606 large calories per day. The daily intake of nitrogen averaged 7.19 grams, while the daily output through the urine was 6.30 grams and in the fæces 0.6 gram;i. e., a daily intake of 7.19 grams of nitrogen, with a total output of 6.90 grams, showing a daily gain to the body of 0.29 gram of nitrogen, and this on a diet containing less than half the proteid required by the Voit standard and having only half the fuel value of the Voit diet. Further, it was found by careful and thorough tests made at the Yale Gymnasium that Mr. Fletcher, in spite of this comparatively low ration was in prime physical condition. In the words of Dr. Anderson, the Director of the Gymnasium, “the case is unusual, and I am surprised that Mr. Fletcher can do the work of trained athletes and not give marked evidences of over-exertion.... Mr. Fletcher performs this work with greater ease and with fewer noticeable bad results than any man of his age and condition I have ever worked with.”[30]It is not our purpose here to discuss how far these results are due to insalivation, or the more thorough mastication of food. The main point for us is that we have here a striking illustration of the establishment of nitrogenequilibrium on a low proteid diet and great physiological economy as shown by the low fuel value of the food consumed, coupled with remarkable physical strength and endurance.
With data such as these before us we see the possible importance of a fuller and more exact knowledge of true dietary standards. We find here questions suggested, the answers to which are of primary importance in our understanding of the nutritive processes of the body; greater ease in the maintenance of health, increased power of resistance to disease germs, duration of life increased beyond the present average, greater physiological economy and greater efficiency, increased mental and physical vigor with less expenditure of energy on the part of the body. All these questions rise before us in connection with the possibility of maintaining equilibrium on a lowered intake of food, especially nitrogenous equilibrium, with a diminished consumption of proteid or albuminous food. Is it not possible that the accepted dietary standards are altogether too high?
It is of course understood that there can be no fixed dietary standard suitable for all people, ages, and conditions of life. Dietary standards at the best are merely an approximate indication of the amounts of food needed by the body, but these needs are obviously changeable, varying with the degree of activity of the body, especially the amount of physical work performed, to say nothing of differences in body-weight, sex, etc. Further, it is doubtless true that there is what may be called a specific coefficient of nutrition characteristic of the individual, a kind of personal idiosyncrasy which exercises in some degree a modifying influence upon the character and extent of the changes going on in the body. Still, with due recognition of the general influence exerted by these various factors the main question remains, viz., how far the usually accepted standards of diet are correct; or, in other words, is there any real scientific ground for the assumption that the average individual doing an average amount of work requires any such quantity of proteid, or of total nutrients, as the ordinary dietetic standards call for? Cannot all the real physiologicalneeds of the body be met by a greatly reduced proteid intake, with establishment of continued nitrogenous equilibrium on a far smaller amount of proteid food than the ordinary dietary standards call for, and with actual gain to the body?
Just here we may emphasize why prominence is given to the establishment ofnitrogenousequilibrium, and why the proteid intake assumes a greater importance than the daily amounts of fat and carbohydrate consumed. Fats and carbohydrates when oxidized in the body are ultimately burned to simple gaseous products, viz., carbonic acid and water. Hence, these waste products are easily and quickly eliminated and cannot exercise much deleterious influence even when formed in excess. To be sure, there is waste of energy in digesting, absorbing, and oxidizing the fats and carbohydrates when they are taken in excessive amounts. Once introduced into the alimentary canal they must be digested, otherwise they will clog the intestine or undergo fermentation, and so cause trouble. Further, when absorbed they may be transformed into fat and deposited in the various tissues and organs of the body; a process desirable up to a certain point, but undesirable when such accumulation renders the body gross and unwieldy. With proteid foods, on the other hand, the story is quite different. These substances, when oxidized, yield a row of crystalline nitrogenous products which ultimately pass out of the body through the kidneys. Prior to their excretion, however, these products—frequently spoken of as toxins—float about through the body and may exercise more or less of a deleterious influence upon the system, or, being temporarily deposited, may exert some specific or local influence that calls for their speedy removal. Hence, the importance of restricting the production of these bodies to the minimal amount, owing to their possible physiological effect and the part they are liable to play in the causation of many diseased conditions. Further, the elimination of excessive amounts of these crystalline nitrogenous bodies through the kidneys places upon these organs an unnecessary burden whichis liable to endanger their integrity and possibly result in serious injury, to say nothing of an early impairment of function.
The present experiments were undertaken to throw light upon this broad question of a possible physiological economy in nutrition, and with special reference to the minimal proteid requirement of the healthy man under ordinary conditions of life. The writer as a student of physiology has always maintained that man is disposed to eat far more than the needs of the body require, but his active interest in this problem was aroused especially by his observations of Mr. Fletcher and the marked physiological economy the latter was able to practice, not only without detriment, but apparently with great gain to the body as regards strength, vigor, and endurance, coupled with an apparent resistance to disease. While Mr. Fletcher and Dr. Van Someren would doubtless emphasize the importance of insalivation as a means of controlling the appetite and thereby regulating the consumption of food in harmony with the real needs of the body, it is of primary importance for the physiologist and for mankind to know definitely how far it is possible to reduce the intake of food with perfect safety and without loss of that strength, mental and physical, vigor, and endurance which are characteristic of good health. Further, it is equally plain that if there is possible gain to the body from a practice of physiological economy in diet, we should know how far this can be accomplished by simple restriction in the amount of food without complicating the problem by other factors.
In planning the conduct of this series of experiments the writer has clearly recognized that, while it may be possible, as previous experiments have shown, to maintain body equilibrium and nitrogen equilibrium on a low proteid diet for a brief period, this fact does not, as Munk has previously pointed out, by any means establish the view that such a diet will prove efficient in maintaining equilibrium for a long period, or that bodily strength and vigor can be kept up and the proper resistance to disease secured. Hence, it seemednecessary to so arrange the experiments that they should continue not for a few days or weeks merely, but through months and years. Further, it is very questionable whether the restricted diet (restricted in variety) frequently made use of for convenience in ordinary metabolism experiments is well adapted for bringing out the best results. Hence, it was decided to avoid so far as possible any monotony of diet, giving due recognition to the psychical influences liable to affect secretion, digestion, etc., so admirably worked out by Pawlow in his classical experiments on these subjects; influences which are unquestionably of great importance in controlling and modifying, in some measure at least, the nutritive changes in the body. Again, it is evident that to have experiments of this character broadly useful, they must be tried upon a large number of people and under different conditions of life, in order to avoid so far as possible the influence of personal idiosyncrasy and thereby escape misleading conclusions.
The experiments have been conducted with three distinct types or classes of individuals:
1st. A group of five men of varying ages, connected with the University as professors and instructors; men who while leading active lives have not engaged in very active muscular work. They were selected as representatives of the mental worker rather than the physical worker, although several of them in the performance of their daily duties had to be on their feet in the laboratory a good portion of the day.
2d. A detail of thirteen men, volunteers from the Hospital Corps of the United States Army and representatives of the moderate worker; men who for a period of six months took each week day a vigorous amount of systematic exercise in the gymnasium, in addition to the routine work connected with their daily life as members of the United States Hospital Corps. These men were of different nationalities, ages, and temperaments.
3d. A group of eight young men, students in the University, all thoroughly trained athletes, and some of them with exceptional records in athletic events.