The nutrition of man

DIETARY HABITS AND TRUE FOOD REQUIREMENTS

Topics: Dietetic customs of mankind. Origin of dietary standards. True food requirements. Arguments based on custom and habit. Relationship between food consumption and prosperity. Erroneous ideas regarding nutrition. Commercial success and national wealth not the result of liberal dietary habits. Instinct and craving not wise guides to follow in choice and quantity of food. Physiological requirements and dietary standards not to be based on habits and cravings. Old-time views regarding temperate use of food. The sayings of Thomas Cogan. The teachings of Cornaro. Experimental results obtained by various physiologists. Work of the writer on true proteid requirements. Studies with professional men. Nitrogen equilibrium with small amounts of food. Sample dietaries. Simplicity in diet. Nitrogen requirement per kilogram of body-weight. Fuel value of the daily food. Experiments with university athletes. Nitrogen balance and food consumption. Sample dietaries. Adequacy of a simple diet.

Having acquired information regarding the principles of metabolism and the general laws governing the nutrition of the body, we may next consider briefly the dietetic habits of mankind, with a view to learning how far such habits coincide with actual nutritive requirements. Eventually, we shall need to ask the questions: What are the true nutritive requirements of the body? How much food and what kinds of food does the ordinary individual doing an average amount of work need each day in order to preserve body equilibrium, and to maintain health, strength, and vigor under the varying conditions of life? What amount of nitrogen or proteid, and what the total calorific value required to supply the physiological needs of the body? How closely do the so-called “normal diets” and “standard diets,” which have met with such general acceptance, conform to a rational conception of true physiological needs? These are vital questions of great physiological and economic importance, and they are not easily answered; but theoretical considerations based on scientific data, and experimental evidence combined with practical experience, should point the way to some very definite conclusions.

Observations made in many countries regarding the dietetic customs and habits of the people have resulted in the establishment of certain dietary standards, which have been more or less generally adopted as representing the requirements of the body. As a prelude to the discussion of this question, let us consider briefly some of the results of these dietary studies. In Sweden, laborers doing hard work were found by Hultgren and Landergren to consume daily, on an average, 189 grams of proteid, 714 grams of carbohydrate, and 110 grams of fat, with a total fuel value for the day’s ration of 4726 large calories. In Russia, workmen at moderately hard labor, having perfect freedom of choice in their food, were found by Erisman to take daily 132 grams of proteid, 584 grams of carbohydrate, and 79 grams of fat, this ration having a fuel value of 3675 calories. In Germany, soldiers in active service consumed daily, according to Voit, 145 grams of proteid, 500 grams of carbohydrate, and 100 grams of fat, with a fuel value of 3574 calories. In Italy, laborers doing a moderate amount of work were found by Lichtenfelt to consume daily 115 grams of proteid, 696 grams of carbohydrate, and 26 grams of fat, with a fuel value of 3655 calories. In France, Gautier states that the ordinary laborer working eight hours a day must have 135 grams of proteid, 700 grams of carbohydrate, and 90 grams of fat daily, with a fuel value of 4260 calories. In England, weavers were found to take daily 151 grams of proteid, with carbohydrates and fats sufficient to make the total fuel value of the day’s ration equal to 3475 calories. In Austria, farm laborers consumed daily 159 grams of proteid, with carbohydrates and fats sufficient to raise the fuel value of the food to 5096 calories.

Observations of this order might be multiplied indefinitely, but the above will suffice to give a general idea of the average food consumption of European peoples doing a moderate amount of work. These data, however, must be supplemented by the observations made in our own country, which have been very extensive, through the “investigations on the nutrition of man in the United States,” carried on by the Office of Experiment Stations in the Department of Agriculture, under the efficient leadership of Atwater. As stated by Messrs. Langworthy and Milner, in an official bulletin issued in 1904, dietary studies of the actual food consumption of people of different classes in different parts of the United States have been made during the years 1894 to 1904 on about 15,000 persons,—men, women, and children,—as a result of which it is indicated that “the actual food requirements of persons under different conditions of life and work” vary from 100 to 175 grams of proteid per day, with a total fuel value ranging from 2700 to 5500 calories. For comparison, the various data may be tabulated as shown on page 155.

These figures by no means represent maximum food consumption. Thus, studies have been made on fifty Maine lumbermen,53 where the intake of proteid food averaged 185 grams per day, with a total fuel value of 6400 calories. Further, dietary studies of university boat crews54 have shown fairly high results. The Yale University crew, while at Gales Ferry, averaged per man during seven days 171 grams of proteid, 171 grams of fat, and 434 grams of carbohydrate, with a total fuel value of 4070 calories per day. The members of the Harvard University crew showed an average daily consumption of 160 grams of proteid, 170 grams of fat, and 448 grams of carbohydrate, with a total fuel value of 4074 calories. It is also reported that a football team of college students in the University of California consumed daily, per man, 270 grams of proteid, 416 grams of fat, and 710 grams of carbohydrate, with a total fuel value of 7885 calories. These figures may be contrasted, however, with the data obtained in a study of the dietary habits of fourteen professional men’s families, where the average amount of proteid consumed daily was 104 grams, fat 125 grams, and carbohydrate 423 grams, with a total fuel value of 3325 calories.

Leaving out of consideration the extremes given, it is undoubtedly true that, within certain rather wide limits, there is an apparent tendency for people of different nations, having a free choice of food and not restricted by expense, to consume daily approximately the same amounts of nutrients; to use what may be called liberal rather than small amounts of food; and, lastly, to consume food somewhat in proportion to the amount of work done. It is perhaps, therefore, not strange that students of nutrition should have taken these results, obtained by the statistical method, as indicating the actual needs of the body for food, and that so-called “standard diets” and “normal diets” should have been constructed, based upon these and corresponding data. Thus, we have the widely adopted “Voit standard,” composed of proteid 118 grams, carbohydrate 500 grams, and fat 56 grams, with a total fuel value of 3055 calories, as the amount of food required daily by a man of 70 kilos body-weight doing a moderate amount of work. These figures were obtained by Voit as an average of the food consumption of a large number of laboring men in Germany, and they carried additional weight because at that time Voit and others thought they had evidence that nitrogenous equilibrium could not be maintained for any length of time on smaller amounts of proteid.

The figures given in the preceding table under the head of American subjects constitute the “Atwater standards,” and as already indicated, are based upon the dietetic habits of over 15,000 persons under different conditions of life and physical activity. In the words of the official Bulletin, these standards covering the quantities of food per day “are intended to show the actual food requirements of persons under different conditions of life and work.” Here, however, lies an assumption which seems to meet with wide acceptance, but for which it is difficult to conceive any logical reason. The thousands of dietary studies made on peoples all over the world, affording more or less accurate information regarding the average amounts of proteid, fat, and carbohydrate consumed under varying conditions, are indeed most interesting and important, as affording information regarding dietetic customs and habits; but, the writer fails to see any reason why such data need be assumed to throw any light on the actual food requirements of the body. In the words of another, “Food should be ingested in just the proper amount to repair the waste of the body; to furnish it with the energy it needs for work and warmth; to maintain it in vigor; and, in the case of immature animals, to provide the proper excess for normal growth, in order to be of the most advantage to the body” (Benedict).

Any habitual excess of food, over and above what is really needed to meet the actual wants of the body, is not only uneconomical, but may be distinctly disadvantageous. Voit, among others, 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. My own conception of the true food requirements of the body has been expressed in the statement that man needs of proteids, fats, and carbohydrates sufficient to establish and maintain physiological and nitrogen equilibrium; sufficient to keep up that strength of body and mind that is essential to good health, to maintain the highest degree of physical and mental activity with the smallest amount of friction and the least expenditure of energy, and to preserve and heighten, if possible, the ordinary resistance of the body to disease germs. The smallest amount of food that will accomplish these ends is, I think, the ideal diet. There must truly be enough to supply the real needs of the body, but any great surplus over and above what is actually called for may in the long run prove an undesirable addition. With these thoughts in mind, may we not reasonably ask why it should be assumed that there is any tangible connection between the dietetic habits of a people and their true physiological needs?

Arguments predicated on custom, habit, and usage have no physiological basis that appeals strongly to the impartial observer. Man is a creature of habits; he is quick to acquire new ones when his environment affords the opportunity, and he is prone to cling to old ones when they minister to his sense of taste. The argument that because the people of a country, constituting a given class, eat a certain amount of proteid food daily, the quantity so consumed must be an indication of the amount needed to meet the requirements of the body, is as faulty as the argument that because people of a given community are in the habit of consuming a certain amount of wine each day at dinner their bodies must necessarily be in need of the stimulant, and that consequently alcohol is a true physiological requirement. A large proportion of mankind is addicted to the tobacco habit, and to many persons the after-dinner cigar is as essential to comfort as the dinner itself; but would any one think of arguing that tobacco is one of the physiological needs of the body?

It is said that dietary studies made all over the civilized world “show that a moderately liberal quantity of protein is demanded by communities occupying leading positions in the world. . . . It certainly seems more than a remarkable coincidence that peoples varying so widely in regard to nationality, climatic and geographical conditions, and dietetic habits, should show such agreement in respect to consumption of protein and energy.” Again, we hear it said that “whatever may be true of a few individuals, with communities a generally low condition of mental and physical efficiency, thrift, and commercial success, is coincident with a low proportion of protein in the diet.” The writer, however, fails to find evidence in the results afforded by dietary studies that there is any causal relationship between the amount of proteid food consumed and the mental or physical supremacy of the people of a given nation or community. Cause and effect are liable to become reversed in arguments of this kind. It is certainly just as plausible to assume that increase in the consumption of proteid follows in the footsteps of commercial and other forms of prosperity, as to argue that prosperity or mental and physical development are the result of an increased intake of proteid food.

Proteid foods are usually costly, and the ability of a community to indulge freely in this form of dietetic luxury depends in large measure upon its commercial prosperity. The palate is an extremely sensitive organ, and the average individual properly derives great satisfaction from the pleasurable effects of tasty articles of food. Furthermore, there are many curious and quite unphysiological notions abroad regarding foods, which tend to incite persons to unnecessary excess and extravagance whenever they acquire the means to do so. The latter point is well illustrated by the more or less prevalent opinion that a cut of tenderloin steak is more nutritious than a cut of round steak. It is true that the former is apt to be more tender, to have a little finer flavor; but the round steak, when properly prepared, is just as nutritious, and equally capable of meeting the needs of the body, as the more expensive tenderloin. With increasing prosperity, we turn at once, as a rule, to the more tasty and appetizing viands, partly to satisfy the craving of appetite and palate, and partly because there is an inherent belief that these varied delicacies, accessible to the prosperous community, count as an aid to health and strength. The poor laborer, with his small wage, is restricted to a certain low level of dietary variety, and must likewise be economical as to quantity, but on the first opportunity afforded by a fuller purse he is apt to pass from corned beef to a fresh roast with its more appetizing flavor; to eschew brown bread in favor of the white loaf, and in many other ways to evince his desire for a dietary which, though perhaps no more nutritious, appeals because of its finer flavor, more appetizing appearance, and greater variety. He is in the same position as the smoker who, limited by his purse to a five-cent cigar after dinner, quickly passes to a cigar of better flavor as soon as his finances warrant the indulgence. At the same time, if prosperity continues, our laborer will speedily pass to a higher level of proteid intake and greater fuel value, through increased consumption of meat and butter, together with other articles rich in proteid and fat.

In this connection, we may emphasize a fact of some significance in its bearing on dietetic customs; viz., that ever since Liebig advanced his theory that proteid material is the sole source of muscular energy, there has been a deep-rooted belief that meat is the most efficient kind of food for keeping up the strength of the body, and hence especially demanded by all whose work is mainly physical. Although this view, as we have seen, has been thoroughly disproved, the idea is still more or less generally held that an abundance of meat is a necessary requisite for a good day’s work, a view which undoubtedly accounts in some measure for the tendency toward a high proteid intake, evinced by many of the laboring class whose means will permit the necessary outlay.

Increased consumption of proteid food may be coincident with thrift and commercial success, but there is no justification for the belief that these are the result of changed dietary conditions. The dietary of our New England forefathers was, according to all accounts, exceedingly limited as compared with that of to-day, but it is doubtful if the present generation is any better developed, physically or mentally, than the stalwart and vigorous people who opened up this country to civilization. To-day, as a nation, we have greater wealth, and our commercial prosperity has become phenomenal; but would any one think for a moment that these characteristics are attributable to the large consumption of proteid food so common to this generation of the American people? No, increased wealth simply paves the way for greater freedom in the choice of food; increased commercial success and business prosperity throw open avenues which formerly were closed; greater variety of animal foods, and vegetable foods as well, rich in proteid, are made easily accessible, and appeal to eye and palate on all sides; appetite and craving for food are abnormally stimulated, and dietetic habits and customs change accordingly. In the words of another, “the one thing that primitive, barbarous, and civilized man alike long for is an abundance of the ‘flesh-pots of Egypt.’ The very first use the latter makes of his increased power and financial resources is to buy new, rare, and expensive kinds of meat.” With these facts before us, it is difficult to accept the assumption that dietetic customs afford any indication of the food requirements of the body. To the physiologist such a view does not appeal, since there is a lack of any scientific evidence that carries conviction.

But it may be asked, is not appetite a safe guide to follow? Do not the cravings of the stomach and the so-called pangs of hunger merit consideration? Is it not the part of wisdom to follow inclination in the choice and quantity of our food? Can we not safely rely upon these factors as an index of the real needs of the body? If these questions are to be answered in the affirmative, then it is plain that a study of dietetic customs will tell us definitely how much food and what kinds of food are required daily to supply the true wants of the body. There are writers who claim that instinct is a perfectly safe guide to follow; that it is far superior to reason; but it is to be noticed that most of these writers, if they have any physiological knowledge to draw upon, are sooner or later prone to admit that the body has certain definite needs which it is the purpose of food to supply, with the added implication that any surplus of food over and above what is necessary to meet these demands is entirely uncalled for. Thus, one such writer states that “the man in the street follows his God-given instincts and plods peacefully along to his three square meals a day, consisting of anything he can find in the market, and just as much of it as he can afford, with special preference for rich meats, fats, and sugars.” Yet this same writer, a little later, emphasizes the fact that “every particle of the energy which sparkles in our eyes, which moves our muscles, which warms our imaginations, is sunlight cunningly woven into our food by the living cell, whether vegetable or animal. Every movement, every word, every thought, every aspiration represents the expenditure of precisely so much energy derived from food.” Why, then, would it not be wise to ascertain how much energy is so expended, on an average, during the day’s activity and govern the intake of food accordingly? Why not apply an intelligent supervision in place of following an instinct which, in the words of the author just quoted, leads one on to consume “anything he can find in the market and just as much of it as he can afford”? Truly, if dietetic customs and the habits of mankind are the results of instinct working in this fashion, there cannot be much value in the data obtained by observing the quantities of food mankind is in the habit of eating. Dietary standards based on such observations must be open to the suspicion of representing values far above the actual needs of the body.

Habits and cravings are certainly very unreliable indices of true physiological requirements. Man is constantly acquiring new habits, and these in time become second nature, forcing him to practise that which he has become accustomed to, regardless of whether it is beneficial or otherwise. The celebrated philosopher, John Locke, in his essay on education, says: “I do not think all people’s appetites are alike . . . but this I think, that many are made gourmands and gluttons by custom, that were not so by nature; and I see in some countries, men as lusty and strong, that eat but two meals a day, as others that have set their stomachs by a constant usage, like Larums, to call on them for four or five.” Again, the so-called cravings of appetite are largely artificial and mainly the result of habit. A habit once acquired and persistently followed soon has us in its grasp, and then any deviation therefrom is very apt to disturb our physiological equilibrium. The system makes complaint, and we experience a craving, it may be, for that to which the body has become accustomed. There has thus come about a sentiment that the cravings of the appetite for food are to be fully satisfied, that this is merely obedience to nature’s laws. In reality, there is no foundation for such a belief; any one with a little persistence can change his or her habits of life, change the whole order of cravings, thereby indicating that the latter are essentially artificial, and that they have no necessary connection with the welfare or needs of the body. The man who for some reason deems it advisable to adopt two meals a day in place of three or four, at first experiences a certain amount of discomfort, but eventually the new habit becomes a part of the daily routine, and the man’s life moves forward as before, with perfect comfort and without a suggestion of craving, or a pang of hunger. Dietetic requirements, and standard dietaries, are not to be founded upon the so-called cravings of appetite and the instinctive demands for food, but upon reason and intelligence, reinforced by definite knowledge of the real necessities of the bodily machinery.

The standards which have been adopted more or less generally throughout the civilized world, based primarily on the assumption that man instinctively and independently selects a diet that is best adapted to his individual needs, are open to grave suspicion. The view that the average food consumption of large numbers of individuals and communities must represent the true nutritive requirements of the people is equally untenable. Naturally, there is general recognition of the principle that food requirements are necessarily modified by a variety of circumstances, such as age, sex, body-weight, bodily activity, etc. It is obvious that the man of 140 pounds body-weight needs less proteid than the man of 170 pounds, and that the man who does a large amount of physical work demands a larger calorific value in his daily diet, i. e., more carbohydrate and fat, than the sedentary individual. The growing child, in proportion to his body-weight, plainly needs more proteid for the upbuilding of tissue, and there are many conditions of disease where special dietetic treatment is undoubtedly called for. Our contention, however, and one which we believe to be perfectly justifiable, is that the true food requirements of the body, under any conditions, cannot be ascertained with any degree of accuracy by observations of what people are in the habit of eating; that customs and habits are not a safe index of true physiological needs. On the contrary, we are inclined to the belief that direct physiological experimentation, covering a sufficient length of time and with an adequate number of individuals, will prove far more efficient in affording a true estimate of the quality and quantity of food best adapted for the maintenance of good health, strength, and vigor.

Before considering these latter points, it is interesting to note, in passing, that during the last four centuries many thoughtful men have called attention to the apparent excessive use of food. There seems to have been in many quarters a more or less prevalent opinion that custom and habit were leading people on to methods of living, which were not in accord with the best interests of the community. It must be remembered, however, that arguments of this kind, even fifty years ago, could have been founded only on general observation and the application of common sense, since there were then no sound physiological data on which to predicate an opinion, or base a conclusion. Still, there were men of authority who attempted to lay before the people a proper conception of the temperate use of food. We have not the time here to consider many of these pleas, but I venture to call attention to the somewhat celebrated book published by the physician Thomas Cogan in 1596, under the title “The Haven of Health,” and dedicated “to the right honorable and my verie good lord, Sir Edward Seymour, Knight and Earl of Hertford.” Under the subject of diet, this old-time writer says: “The second thing that is to be considered of meates is the quantitie, which ought of all men greatly to be regarded, for therein lyeth no small occasion of health or sickness, of life or death. For as want of meate consumeth the very substance of our flesh, so doth excesse and surfet extinguish and suffocate naturall heat wherein life consisteth.” Again, “Use a measure in eating, that thou maist live long: and if thou wilst be in health, then hold thine hands. But the greatest occasion why men passe the measure in eating, is varitie of meats at one meale. Which fault is most common among us in England farre above all other nations. For such is our custome by reason of plentie (as I think) that they which be of abilitie, are served with sundry sortes of meate at one meale. Yea the more we would welcome our friends the more dishes we prepare. And when we are well satisfied with one dish or two, then come other more delicate and procureth us by that meanes, to eate more than nature doth require. Thus varietie bringeth us to excesse, and sometimes to surfet also. But Phisicke teacheth us to faede moderately upon one kinde of meate only at one meale, or at leastwise not upon many of contrarie natures. . . . This disease, (I mean surfet) is verie common: for common is that saying and most true: That more die by surfet than by the sword. And as Georgius Pictorius saith, all surfet is ill, but of bread worst of all. And if nature be so strong in many, and they be not sicke upon a full gorge, yet they are drowsie and heavie, and more desirous to loyter than to labor, according to that old maeter, when the belly is full, the bones would be at rest. Yea the minde and wit is so oppressed and overwhelmed with excesse that it lyeth as it were drowned for a time, and unable to use his force.”

Cogan likewise makes some interesting statements regarding the effects of custom on the consumption of proteid food, especially meats. Quoting further from this author: “The fourth thing that is to be considered in meats is custome. Which is of such force in man’s bodie both in sicknesse and in health, that it countervaileth nature itselfe, and is therefore called of Galen in sundry places, an other nature. Whereof he giveth a notable example, where he sheweth that an olde woman of Athens used a long time, to eate Hemlocke (which is a ranke poison) first a little quantitie, and afterwarde more, till at length she could eate so much without hurt as would presently poison another. . . . So that custome in processe of time may alter nature.” Finally, we may quote one last saying of Cogan’s, because of the good sense and wisdom displayed in the sentiment, as true to-day as when it was written more than three hundred years ago: “Neither is it good for any man that is in perfect health, to observe any custome in dyet precisely, as Arnoldus teacheth upon the same verses in these wordes: Every man should so order himselfe, that he might be able to suffer heate and cold, and all motions, and meats necessary, so as he might change the houres of sleeping and waking, and his dwelling and lodging without harme: which thing may be done if we be not too precise in keeping custome, but otherwise use things unwonted. Which sentence of Arnoldus agraeth verie well to that of Cornelius Celsus: He that is sound and in good health, and at libertie, should bind himselfe to no rules of dyet. To need neither Phisition or Chirurgion, he must use a diverse order of life, and be sometimes in the countrie, sometime in the towne, sometimes hunt, and sometime hawke. But some man may demand of me how this may agree with that saying of the scholar of Salernus ‘if you would be free from physicians, let these three be your physician, a cheerful mind, rest, and a moderate diet.’ Whereunto I answer, that a moderate dyet is alwaies good, but not a precise dyet: for a moderate diet is, as Terence speaketh in Andria: To take nothing too much: which alwaies is to be observed. But if a man accustome himselfe to such meats and drinks as at length will breed some inconvenience in his bodie, or to sleepe or to watch, or any other thing concerning the order of his life, such custome must naedes be amended and changed, yet with good discretion, and not upon the sudden: because sudden changes bring harme and weaknesse, as Hippocrates teacheth. He therefore that will alter any custome in dyet rightly, must do it with three conditions, which are expressed by Hippocrates. Change is profitable, if it be rightly used, that is, if it be done in the time of health, and at leisure, and not upon the sudden.”

This noteworthy book written by Cogan was preceded by the writings of Louis Cornaro, the Venetian, who forty years before had published the first edition of his celebrated book, “The Temperate Life,” and who was a most ardent advocate of the benefits to be derived by living temperately, especially in matters of diet. The simple diet which served for the nourishment of the oldest peoples of Syria, Greece, Egypt, and of the Romans when they were at the height of their prosperity and culture, was advocated by Cornaro as conducing to longevity, better health, and greater comfort of mind and body. Himself a striking example of the effects of a reasonable abstinence in diet (the last edition of his book having been written at the age of ninety-five), his teachings have continued to attract attention down to the present day; and although we have no values in grams or calories expressive of his average food consumption, it is quite evident that Cornaro lived a very abstemious life, eating little of the heavier articles of diet common to his time and country. It is perhaps not strictly physiological to refer to these cases, yet they have value as representing a sentiment, common to the centuries now passed, that benefit was to be derived by mankind from greater care in the taking of food; that prevalent customs and habits were leading the people into intemperate modes of life, and that these were surely tending toward the physical and mental deterioration of the nation. We may attach much or little weight to these conclusions, but there is a certain degree of significance in the views, current then as now, that dietetic customs and habits have no real connection with bodily requirements.

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, Hirschfeld55 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 Voit56, 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 Glässner59 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: