This book is DUE on (he last date stamped below STATE NORMAL HARVARD HEALTH TALKS THE CAKE OF CHILDREN 11V JOHN LOVETT MOUSE I'HF_-EHVATI\ES AND OTHER CHEMICALS IN FOODS: THEM tsE AND A1H>E UV OTTO FOLIN THE CAKE OF THE SKIN IIV CHAHl.E> JAMES WHITE THE ( A HE OF THE r-ICK H(M)M HV F.I.IMI1N.E (.EHH\ Cl II. KH 1HK f'AHE OF 'HIE IKl.lll IIV CHAHI.E> AI.I1KH1 HHACKE'IT ADENOIDS AND TONHl.s nv AI..I:HNO.> < OOI.HM.E AN ADKlJlMi: DIET ItV I'EHi V (.(il.DIHU \1I -lll.l:.- IIOU 1) \\ i 'ill INI li I H >\- IIV < II \HI.E- \ \I.I I. 11 \I'IN HARVARD HEALTH TALKS HARVARD HEALTH TALKS AN ADEQUATE DIET nr PERCY G. STILES, PH.D. ASSISTANT PHOFESSOH Or PHT81OLOOT IN HAHVAIIO CNIVEKITT CAMBRIDGE HARVARD UNIVERSITY PRESS 1916 IIAHVAKl) L'XIVKlt-XITY 1'KKS.H Kirt inipn-v>i<>n. Ort'-lwr. 1U10 >->mil iuii>rrMr>, Jaiiun-. 1BIT HARVARD HEALTH TALKS PRESENTING tin* substance of some * of the public lectures delivered at the Medical School of Harvard Univer- sity, this series aims to provide in easily accessible form modern and authorita- > tive information on medical subjects of general importance. The following committee, composed of members of the Faculty of Medicine, has editorial supervision of the volumes published: EDWARD IIICKLING BRADFORD, Qj A.M., M.I)., Dean of the Faculty of Medicine, and Professor of Orthopedic Surgery, Emeritus. HAROLD CLARENCE ERNST, A.M., M.I)., Professor of Bacteriology. WALTER BRADFORD CANNON, A.M., M.D., George Higginson Professor of Physiology. AN ADKQIATE DIET ACKNOWLEDGMENT Acknowledgments are due to the W. B. Saunders Company of Philadelphia for waiving contract rights in permitting the publication of this material. AN ADEQUATE DIET THE PROBLEM THE past few years have been a period of great and fruitful activity for the biological chemist. When one surveys the results that have been amassed, one feels that the requisites of diet are so numerous as to make failure in nutrition altogether more probable than success; it seems scarcely possible that all the known demands shall be sat- isfied. But as a corrective upon this im- pression, we have before us the fact that the human race, without scientific guid- ance, has maintained through the ages a fair measure of health and power. In view of this one may incline to think that scientific discoveries in the field of dietetics are academic rather than practical. 11 HARVARD HEALTH TALKS A judicial mind will hold to a middle course. '1 here need he no discourage- ment because the requirements are so many; on the other hand, it is not the part of wisdom to discount all that has come from the chemist's patient labor. Kven though mankind has survived, we can concrive that human .standards may he bettered. If this is true of the race, it is much more conspicuously true of ill-nourished individuals. AVe must con- sider in what respects the conditions of modern life have modified habits of diet, and whether, in any instances, the changes have been for the wor>e. The ease is paralleled by that of the man who begins to consider the possibili- ties of disease. 1 here arc M> many mala- dies to be thought of that the retention of health seems like keeping one's balance on a tight-rope. ^et. if the preservation of health is really a tight- rope performance, there is a factor which gives constant .support, the remarkable AN ADEQUATE DIET stability of health in the normal subject - his constitution which is like a gyroscope in its steadying effect. Here, too, it is rational not to ignore the dan- gers, but at the same time to recognize our relative security. THE SERVICE OF FOOD Adequacy of diet is a matter both of quantity and composition. The two phases of the question can be considered to greater advantage, if we first briefly recall the purposes which food subserves. These may be said to be three growth, repair, and operation. It might be thought that repair would prove to be typical growth, offset by disintegration, but we have recent evidence that growth has features distinguishing it quite clearly from the processes of main- tenance. In the child, a moderate part of the diet is incorporated into the increasing mass of the tissues. Later, when these 13 HARVARD HEALTH TALKS are no longer on the increase, a rather small, hut perfectly definite, fraction of the food taken is still devoted to com- pensation for their wear and tear. But. first and last, the major part of the foot! serves for the operation of the mechan- ism, and can be correctly described as fuel. The body may be likened to a jM)\ver-house which had to be built from certain materials, maintained by other supplies, but which is operated, day by day, at the co.st of vast quantities of coal. It is clear that, in the long run, the coal may greatly outweigh the machinery and the structure which hou.M-s it. Our analogy is faulty, of course, par- ticularly in that the power-house is not operated until it ha> been completed, while the human organism i> active from early embryonic life, burning fuel, and setting the energy free while its construc- tion goes steadily on. There is another re>peet, however, in which our compari- 11 AN ADEQUATE DIET son is entirely justified. For purposes of construction it is necessary to have precisely the right materials; among fuels there is a greater possibility of sub- stitution. Just as the plan of,the builder calls for wood in one place, steel in an- other, and glass in a third, so the devel- opment of the human frame requires a larger number of distinct and specific sup- plies than we realized a short time ago. Plainly, the diet must furnish material adapted, first to make, and always to maintain, the sum of all the tissues. In other words, it must bear a certain like- ness to the body it is to nourish. But it need not be rigidly similar, for the cells have a capacity to transform certain compounds into others. Thus it is pos- sible to make haemoglobin, the valuable red pigment of the blood, from vegetable substances^ which seem quite remote from it in their chemical nature. A hundred years ago physiologists thought that animals had to obtain all their HARVARD HEALTH TALKS necessary constituents, ready-formed, from the plant world. This is by no means the case; many syntheses are carried out by animal tissues. \ et the constructive power has its limits, and sometimes tlioe are unexpectedly mani- fested. TRADITIONAL STANDARDS There arc t \vo standards by which, in the past, diets have been appraised, (hie of these is tin- fuel value. It U clear that this i> one criterion which must be satis- fied, though it dor-, not by itself show that a ration is suilicient; it is merely a measure of quantity, and not an indica- tion of suitable composition. The unit of fuel-value is the larjje calorie, which is primarily a standard quantity of heat. Since one form of elleivy call be eon- Verted into another, the calorie may stand not only for heat but 1 for ii'urk, which is the second LMvat item in the dynamic out|)iit of the body. AN ADEQUATE DIET The heat value of an average diet may be set down as twenty-five hundred calories'per diem. This is for an individ- ual doing hut little physical work. The allowance for such subjects may be scaled down to two thousand but must be increased for those whose labor is heavy. Farmers, the world over, seem to require about thirty-five hundred calories. A maximum in the vicinity of seven thousand has been recorded for the Maine lumberman. It is interesting to note that an alcohol lamp, burning a pint of its proper fuel in twenty-four hours, is as large a source of heat and, poten- tially, of other energy as an average man. PROTEIN The second standard by which diets have been judged is their protein content. Proteins are the compounds in our foods which most nearly resemble the leading constituents in muscles, glands, and liv- ing tissues generally. There is no doubt 17 HARVARD HEALTH TALKS of their peculiar importance for growth and for the upkeep of the organs. l>ut it has proved difficult to fix upon the ideal amount for these services. Most people, choosing their food with no thought of its nature and guided only by appetite, take from two to three ounces (fifty-six to eighty-four grains) daily. It has com- monly been held that a selection so widely concurred in cannot he far wrong. Are we always safe in assuming that the average practice is the best possible ? It may he urged that the lower ani- mal* have no guide but in.stinct. If they are well nourished, cannot man be tru.sted t< choose his food !" This does riot necearily follow. Man " has sought out many inventions," and in- .stinct becomes an uncertain counsellor when in the midst of artificial conditions. It is, in fact, true of domestic animals that the agricult urUt may .select a ration that i.s probably better for them than any of their own choosing. Is AN ADEQUATE DIET We may assume that our remote an- cestors had a restricted choice of food, that they were frequently on short com- mons, and that they were seldom tempted to eat merely to enjoy varied flavors. Appetites adapted to their lot would lead to over-consumption if in- herited by descendants having access to food of many kinds. This argument may he applied either to the question of total quantity or to that of the protein allowance. Sylvester Graham thought that a meal should consist of but one course, and there is, perhaps, no better safeguard against over-eating than this simple principle. If proteins were of no use but for con- struction like the bricks, tiles, and glass brought to our hypothetical power- house, there would evidently be no value in an excess over the current require- ment. They are actually more adapt- able than this; they are more like lum- ber which can be turned to account as a HARVARD HEALTH TALKS furl supply if not needed for building material. A strong .suggestion is con- veyed that such use of proteins is some- what extravagant, and this is probably just. The objections to the consumption of much protein food may be concisely stated. AVTO-lNTOXICATION These objections fall into two classes. First, we have to reckon with certain peculiarities of proteins when they are acted upon in the alimentary canal. All types of food undergo decomposition - a.s distinguished from digestion while in the intestine. The extent of the changes is probably greatest in the case of the .sugars, and least with the fats. 1'roleins are intermediate in the degree of their decomposition, but it is well established that the products arising are peculiarly harmful, ('ertain of the pro- ducts, carried far and wide by the cir- culation, have power to injure thegeneral 20 AN ADEQUATE DIET health. Any form of disturbance due to them may be called a symptom of auto-intoxication . Certain mild effects have long been referred to this source. Among them have been headache, drowsiness, and quick susceptibility to fatigue. It is now believed that much graver ills may originate from abnormal decomposition in the tract, and the entry of poisons into the system. Troubles with the joints, anaemia, and serious nervous disorders may be mentioned. It is clearly important in all such cases to keep down the protein of the ration. The decom- positions which do so much harm result from the activities of the swarming micro-organisms of the intestine. Our natural defense is the prompt absorption of the products of digestion and the consequent absence of a lagging surplus. In addition to the drawbacks of a protein excess in the canal, we must recognize that bad effects may arise HARVARD IIKALTH TALKS from Mich excess, even though the protein l>e perfectly di^oted and al>- sorled. In the normal course of events, all the starch, and the several sugars, which \ve eat will lie offered to the tissues in the form of .simple sugars < two or three varieties i. All the fat of our food will figure a^'ain as fat when transferred to the Mood. 'NMien. later, sugars and fats are hurried oxidi/ed) under the usual conditions of life, only two products arise. The>e are carbon dioxid and water. Their removal is a >ini|)le mat- ter: the carlxm dioxid passe- out in the breath; tin- water l>l-nds \\ith a much larger voluiiu* which i> always passing through the lody, and is cared for ly all the channels of excretion. It i^ otherwise \\hen protein is treated as a fuel, ('arl)on ul>ject . Tin: V.M.ri-: <>r MINOR C<>\- STITfKXTS There are l>ut few articles of human con- sumption which do not prove, upon chemical investigation, to lie mixtures of many compounds. Kven our drink- ing water contains >alts and other bodies in solution. ( 'anc-sugar comes as near l>eing a single pure compound as anything we eat. and this it is our prac- tice to comliine with other foods. Sugar ha> heen condemned for the very reason that it is a purified and homogeneous compound, and therefore not a " natu- r;il " food. This does mil scnn an im- I>res^ive argument, so lon.i; a> there are many contracting fd<)(U in the diet, luit it is certain that we cannot ^ f o on indefinitely reducing the numlier of com- AN ADEQUATE DIET pounds without sooner or later exclud- ing something essential to nutrition. The minor constituents, in which there is so much interest at this time, are partly organic, and partly mineral. The belief that mineral supplies in a certain variety are necessary to health is not new. During growth it is as truly re- quisite to provide these as to furnish the proteins themselves. The ash left he- hind when milk is first evaporated and then burned has been shown to be mar- vellously adapted to its special service, the production of standard tissue. The organic ingredients of the accessory class deserve rather full treatment. They are useful, first of all, because to a great extent they determine the pala- tability of food. This is very far from being merely an aesthetic consideration. iMeals must be relished if they are to be well digested. Proteins, starch, and fats in pure condition are tasteless, and aside from the sweetness of the sugars, all the 27 HARVARD HEALTH TALKS numberless flavors we enjoy are due to the accessories, mineral and organic.' The latter are much the more important, for the salts are odorless. Some of the extractives, notably those in meat, directly stimulate the lining of the stomach so as to promote the secretion of the gastric juice. But the accessories are not significant for digestion alone; they have a most striking relation to nutrition. Their presence in suitable assortment is im- perative. The recognition of this fact is clearing up many matters that have been perplexing. It has been hard to account for the obvious inequality in nutritive value which is often demon- strated for diets equivalent iii calories and protein content. It has been clearly shown that of two such diets one may be ample for all purposes, and the other inadequate, simply because the first con- tains minute quantities of substances not found in the second. AN ADEQUATE DIET Reference has been made to Sylvester Graham. We shall do well to examine one of his chief doctrines which is enjoy- ing something of a revival in our day. The flour which bears the name of (Ira- ham contains all parts of the wheat kernel, the husk as well as the interior. This reformer taught that by rejecting the husk we might fail to obtain some essential fraction of the food. This was a shrewd induction. It has been defi- nitely proved that when the envelope or pericarp of rice is discarded, the grain ceases to be a complete food for pigeons. An active principle can be prepared from the pericarp which will perfectly remedy the deficiency when supplied in minute quantities. What goes wrong in the economy of the pigeon which is restricted to a diet of polished rice ? The question can be answered with some precision. The compound which the ration fails to furnish is needed most urgently by the 21) HARVARD HEALTH TALKS nerves. If it is not afforded by the food, a limited supply can l>e had from other tissues of the body, luit at a heavy cost: the structures levied upon disintegrate. It is as though holts were removed from one machine to repair another with the result that the lir>t fell to pieces. 'When the nerves can no longer he sustained. even ly this ruinous process, they he- come definitel diseased. The failure of nutrition in the pigeon is believed to correspond rather closely with the (li>ease of man known in the Kast as beri-beri. People restricted by habitat and poverty to a monotonoii> diet are sometimes observed to lose rapidly in weight and >| ivni:th. and then to develop acute nervous lesions (poly- neuritis). Ileri-heri lias always been banished from communities in \\hich the food-supply has become more ample and inclusive. AN ADEQUATE DIET SCURVY Similarly, it has been believed that scurvy is a deficiency disease. The chronicles of explorers abound in in- stances of this distressing malady. The victims have been prostrated, have suf- fered intensely from sore mouths, have had haemorrhages under the skin, friable bones, and a long list of other symptoms. Various articles, such as lime-juice and potatoes, have seemed to be efficacious in warding off and relieving scurvy. Some have contended that scurvy is a form of poisoning due to products of decomposi- tion developing in the food. It seems more in accord with the facts, however, to assume, not that the food has come to contain a poison, but that some valu- able constituent has disintegrated. The lime-juice or the potato, then, does not convey the antidote to a poison, but rather an ingredient similar to that one which has been lost. 31 HARVARD HEALTH TALKS VlTAMINES It has been proposed to call the valuable substances for want of which beri-beri, scurvy, and other disorders arise, by the name of ritanrine.i. An uininc is a nitro- genous compound of a certain type, while the prefix suggests that a vitamine is such a coni]X)iiiul as is necessary to life. The objection has been raised that the term is too .specific; we do not know that all such bodies are amines, nor even that they are nitrogenous; it is probable that .some of them are neither. Hence it seems better to call them acces- sory substances, and not to insist on a chemical classification. Let us now consider quite fully in what ways the human system may fail to re- ceive any of the .supplies necessary to its welfare. The suggestion from beri-beri is to the effect that this may happen when the selection of food is too re- stricted. Furthermore, we recogni/e .TJ AN ADEQUATE DIET the possible impairment of food-values by refining. But we may repeat that there can be no serious objection to this refining when it is applied only to a moderate part of the diet. A condition which many hold to be analogous to beri-beri is the grave dis- order, pellagra. This is a disease of grad- ual development. The early symptoms are confined to the skin; later, the manifestations are widespread, and at the last violent insanity may supervene. Pellagra has long been recognized in Mediterranean countries, and its pres- ence in our own Southern States is now frequently reported. It is generally found to have attacked those whose food is of but few kinds. Like beri-beri, it is usually arrested if the diet is enriched. Meat and milk are especially beneficial. It is, however, not yet certain that pel- lagra is a deficiency disease. When a number of people closely associated suffer from a disorder, the first impres- 33 HARVARD HEALTH TALKS sion is that it has spread among them as an infection; hut we have also to con- sider that it may he the uniformity of their environment and diet, rather than their contact, which has led to like effects in many individuals. These alternatives in the case of pellagra are still heing debated. ( 'OOKIM; So far we have dwelt upon two concep- tions: first, that nutrition may suffer from a narrow selection of food; .second, that long keeping may re>ult in a loss of accessories. Are there still other condi- tions to he reckoned with ? It may prop- erly he asked whether cooking may not have some damaging influence. There are those who actively advocate un- cooked rations, and who themselves live on fruits, nuts, and greens, perhaps making use also of milk. Here, as in many another extreme teaching, we can discover a measure of truth. Some AN ADEQUATE DIET valuable substances in food may very probably be destroyed by strong heating. But we need not hasten to join such a cult. The most that we are required to concede is that we ought to eat a fair amount of raw food. \Ve need not forego the great advantages which, in the case of many articles, are secured by cooking. These include development of flavor, the breaking open of vegetable cells to per- mit the digestion of their contents, and, above all, the destruction of disease- producing germs. Cooking greatly ex- tends the range of our choice, and w r e have been urging all along that safety is found in inclusiveness. FAULTY ASSIMILATION When nutrition, in spite of the best and most varied fare, falls short of success, we may think of still another possibility. Just as foods may be impaired by radical or gradual decomposition before they are eaten, so they may deteriorate in a dis- 35 HARVARD HEALTH TALKS ast rous inaniHT before being absorbed. The slip may not come between the cup and the lip, but between the lip and the circulation. We have often to remind ourselves that what is within the intes- tine is not yet within the body; it is merely in contact with its surface, and subject still to accidental alterations. Finally, it is possible that all the ma- terials needed for the nutrition of the body may be presented to the cells whose duty is to absorb them, and the la.st step may fail to be taken. In other words, there may be faulty assimilation. When a baby does not do well, this is probably the case. The fact that the milk was originally adequate may be shown by the successful nutrition of other infants having the same supply. Non-success, in a particular instance, may be due either to an unfortunate type of intestinal decomposition or to deficient absorption. While we have to admit this possi- bility, we ought at the same time to 30 AN ADEQUATE DIET point out how loose art 1 many statements commonly made regarding variations in assimilation. It is often suggested that one person gets " more of the goodness of his food " than does another. In this way the attempt is made to explain why reputed large eaters sometimes remain thin. But the evidence goes to show that individual differences between persons in fair health are never striking. That is to say, they are not large in a quantitative sense. PERCENTILE ABSORPTION The alimentary canal, even when seri- ously mistreated, usually retains a high degree of efficiency. Unless food is of a very intractable character, not more than ten per cent goes to waste. Some- times the loss by imperfect absorption is as little as five per cent. It is therefore absurd to talk of improving absorption by fifty or a hundred per cent. Little absolute gain, in this respect, can be HARVARD HEALTH TALKS hoped for as a result of prolonged masti- cation or any other special practice. Nevertheless, as we have implied above, a slight improvement as measured by percentage may have a material in- fluence on nutrition, some accessory which previously escaped the organ- ism being secured for its service. It would not be wise, however, to make much of this suggestion, which is frankly speculative. St M.MAKY It will be well now to recapitulate the points which have gone before. The diet must satisfy the fuel requirement of the body. It must furnish suitable pro- teins, and it is better that these should be derived from numerous, rather than u few sources. (This does not mean that a single meal should be complex, but that there should be variety from day U> day.) Mineral matter is a definite need. An unknown number of accessories are AN ADEQUATE DIET required if all is to go well through long periods of time. It may not at present be possible to know in every instance whether a given food possesses virtue by reason of its organic or its mineral composition. Perhaps we need not add further to the list of absolute requirements; but there are other desiderata. Some of these are so obvious that they may be passed over with a word. The importance to us of food which appeals to the appetite should be plain without an argument. It may be said that we should eat what we like. Our liking is, as a rule, the guarantee of digestion. Yet, recalling our plea for inclusiveness, we are bound to add at once that they are fortunate who like a great many kinds of food. ROUGHAGE We speak of certain foods as relatively indigestible. What we usually mean is 39 HARVARD HEALTH TALKS that tlif articles in question cause discomfort or downright disturbances. Many people have perhaps never re- flected that a certain amount of totally indigestible matter may be harmless, if not advantageous. The distinct useful- ness of a moderate quantity of husk and woody fibre is generally affirmed. (Grant- ing that we may extract certain acces- sories from such a source, we must still admit that the mass of the material makes no contribution to the body. It has been spoken of as " ballast," and also as " roughage." In what ways can indigestible matter be helpful ? The assumption is com- monly made that it stimulates the intes- tinal lining by direct contact and pro- vokes a vigorous muscular reaction. This may not be precisely the way in which roughage corrects tin- evil> of con- stipation, but there i> little doubt that the general influence is good. \\ e may suppose that such material, as it is 10 AN ADEQUATE DIET moved along the alimentary canal, catches and takes with it accumulations which might not otherwise have the necessary bulk to be acted upon. Its function would thus be amusingly like that of the saw-dust which the janitor throws upon the floor before sweeping. It may be possible to include too much roughage in the ration, but the opposite practice is probably more common. The principal substance which can figure in this role is cellulose, an indigestible com- pound furnished most abundantly by fruits and coarse vegetables. The agar- agar preparations often used to over- come constipation are substitutes for cellulose, or, in its presence, may supple- ment and reinforce it. In this connection it should be pointed out that the deliberate choice of foods containing a maximum of innutritions matter is favorable to weight reduction, for rations distinguished by bulk rather than actual food value may fairly well 41 HARVARD HEALTH TALKS appease the appetite, while failing to meet the full needs of the tissues. The fat man can replace his bread and butter, potato, pastry, and candy with salads, greens, and fruits, but he may be obliged to continue his new regimen as long as he lives. FIKI. FOODS What .shall we say of the fuel foods ? These enter the body, not to become an enduring part of it, but to be oxidi/.ed to .supply current need>. \N e have im- plied that when this is the service to be performed the substitution of one type of food for another can be quite freely practised. The obvious question is as to whether ;my fixed proportion between fats and carbo-hydrates can be decisively recommended; but about this matter it seems impossible to make dogmatic statements; the ratio has to be deter- mined largely by individual tastes and the capacity of the subject to assimilate 42 AN ADEQUATE DIET one kind or the other. There is also an economic consideration; carbo-hydrates are, in general, much cheaper than fats. The fact is familiar to the dietitian that fats and carbo-hydrates have very different fuel values. If an ounce of fat is to be replaced with carbo-hydrate, it will not answer to supply an ounce of the latter; it will take more than twice as much to provide equivalent energy. The technical statement is that a given weight of fat is isodynamic with about two and a quarter times as much starch. STARCH AND SUGAR A word may be said about the differences between starch and sugar. These two orders of carbo-hydrates are nearly re- lated; in the plant world the change of one into the other is continually taking place. The starches are relatively in- soluble; the sugars dissolve freely. In the course of digestion, starch is changed to sugar. The student, on learning this, 43 HARVARD HEALTH TALKS naturally asks why the sugar might not have been eaten instead of the starch, and the digestive transformation omit- ted, but reasons for preferring to use a good deal of starch are not difficult to find. Highly soluble bodies are always irri- tating to living membranes. This is readily recognized in the case of salts. In the case of the sugars, it is really demonstrated by their sweetness; for the stimulation of the organs of taste is an example of irritation. Starch, which does not give rise to sensations of taste, is correspondingly unstimulating to the cells in general. The formation of sugar from starch in the canal is a relatively gradual process and cannot produce a concentrated solution, provided absorp- tion fairly keeps pace with it. The ad- vantages of .starch over sugar as the chief carbo-hydrate of the diet .should be apparent. 41 AN ADEQUATE DIET ALCOHOL Is regularly consumed by millions of human beings in quantities which give il a material importance in the diet. A recent writer (Dodge) points out that alcohol makes a larger contribution to the fuel value in multitudes of cases than protein does. This is likely to be true whenever the daily consumption of al- cohol is in excess of two ounces. People who use alcohol to this extent presum- ably eat less carbo-hydrate and fat than they would if abstaining; otherwise, they would become corpulent. To admit that alcohol may bear its part among the other fuels, is not to ignore the drawbacks and possible dangers of its inclusion. OVER- AXD UNDER-FEEDING Finally, we may give some attention to the results of general over- and under- feeding. "NYe have already discussed high and low protein standards. It 4.-) HARVARD HEALTH TALKS remains to compare the effects of exces- sive and deficient calorific supply. Cer- tain persons are reputed to he large eaters and others to get along with u little. No doubt, we usually exaggerate the degree of contrast, but moderate differences appear to exi>t. One person may live upon a scale of twenty-five hundred calories, while another, with similar " build " and occupation, may find two thousand sufficient. Numerous experiments have shown that what is called the " ba>al metabol- ism " the energy requirement during rot and fa>ting- does not vary much among healthy Mihjeets. There are probably more di>tinet personal differ- ences when work is performed or low temperatures are encountered. Some organisms may be more economical and efficient than other>. \\lieii we M e a florid man, we are apt to gue>> that he !> a heavy eater. It i> po^ihle that he ha> inherited a >y>tem \\hieh is prodigal Hi AN ADEQUATE DIET in dispersing heat, and that his dietetic habits are necessary to its upkeep. If it is true that such conditions occur, they may remind us of the poorly built and draughty houses which call for such a great consumption of coal to warm them. If we grant that some people need more food than others under like cir- cumstances we have still one important indication to consider, namely, body- weight. The reliability of appetite is impressively shown, in the great ma- jority of cases, by the constancy of the weight through long terms of years. A very small surplus of income over oxida- tion, day by day, will soon result in obesity, while an equally small deficit will lead to emaciation. It is not strange that these imperfect adjust- ments should be frequently observed. The most common instance is the per- sistence of an appetite suited to an active life into years of lessening oxida- 47 HARVARD HEALTH TALKS tion. The resulting increase of weight is in every way undesirable. What are the characteristics of the over-fed and thr under-fed? While there are probably exceptions to the rule, the two types may be expected to appear somewhat as follows. The fir>t is heavy, and of a high color. The man of this class is a deep sleeper, and di>likes to get up; he U an optimist, but not remarkably persevering. The sparingly fed individual is consistently opposed to the liberally nourished at every point. Ife is under weight, and often deficient in color; a light sleeper, if not actually troubled by insomnia; and sensitive to cold. As a worker he may be diligent and efficient, though the temperament exhibited is likely to be eon-eieii 1 1< ills rather than enthusiastic. The high degree of endurance often noted in men ;md \\omen \\lio eat lightly affords the strongest argument m favor of Mich .self-denial. It is probably to be AN ADEQUATE DIET explained l>y two circumstances. First, the intestine is to an exceptional degree free from injurious residues. Seeond, the blood and other body-fluids are corre- spondingly free from avoidable by-pro- ducts of metabolism. The resistance to fatigue secured is greatly to be coveted, but it is not unlikely that the cutting down of the food is often too rigorous. Depression of spirits is a common sign that the diet should be made more generous. 49 HARVARD HEALTH TALKS A FEW REFERENCES Lusk, The Fundamental Baft in of Nutri- tion. Yale University Press, 1014. Mendel, Change* in Food Supply. Yale University Press, 1015. Sherman, Food Products. Macmillan, New York, 1914. Bailey, Source, Chemistry, and Use of Food Products. Blakiston, Philadel- phia, 1014. Meltzer, " The Factors of Safety in the Animal Structure and Economy," Jour, of Amer. Med. Assoc., 1007, vol. xlviii, p. 655. Chittenden, Physiological Economy in Xutrition. Stokes, New York, 1004. Lusk, Elements of the Science of Nutrition. Saunders, Philadelphia, 1000. ol TIIF IIAEVARD I'NlVKBilTY PfctSS MASS , f . S A.