The nutrition of man

by R. H. Chittenden

Dietary habits should be brought into conformity with the true needs of the body. Excessive consumption of proteid food, especially, should be avoided on the ground that it is not only unnecessary and wasteful, but is liable to bring penalties of its own, most undesirable and wholly uncalled for. We may, perhaps, accept these statements at their full value, and yet have a shadow of doubt in our minds as to whether, after all, dietary customs do not harmonize sufficiently at least with true nutritive requirements. All the data that we have presented in the preceding chapters, however, have seemingly given a positive answer to such doubts, and indicate quite clearly that the results of scientific study are opposed to the prevailing dietary standards, especially as regards proteid food. As the celebrated physiologist Bunge has expressed it, “The necessity for a daily consumption of 100 grams of proteid is incomprehensible, so long as we do not know of any function of the body in the performance of which the chemical potential energies of the destroyed proteid are used up.”

Perfectly trustworthy evidence is at hand showing that the needs of the body for potential energy can be fully met, and indeed are more advantageously met, by the non-nitrogenous foods, carbohydrates and fats. The energy of muscle work, as we have seen, comes preferably from the breaking down of non-nitrogenous material, so that there is no special call for proteid in connection with increased muscular activity. In fact, it would appear that the need for proteid food by man is limited to the requirements of growth and development, reinforced by the amount called for in that form of tissue exchange which we have emphasized under the term “endogenous proteid metabolism,” or true tissue metabolism. To be sure, there must be a certain reserve of proteid, available in case of emergency, but this is easily established without resorting to excessive feeding.

The peculiar position which proteid foods occupy in man’s dietary naturally make them the central figure, around which the other foods are grouped. No other form of food can take the place of proteid; a certain amount is needed each day to make good the loss of tissue material broken down in endogenous katabolism, and consequently our choice and combination of the varied articles of diet made use of should be regulated by the amount of proteid they contain. But while proteid foods occupy this commanding position, it is not necessary or desirable that they should exceed the other foodstuffs in amount, or indeed approach them in quantity. We must be ever mindful of the fact, so many times expressed, that proteid does not undergo complete oxidation in the body to simple gaseous products like the non-nitrogenous foods, but that there is left behind a residue of non-combustible matter—solid oxidation products—which are not so easily disposed of. In the forceful language of another, “The combustion of proteid within the organism yields a solid ash which must be raked down by the liver and thrown out by the kidneys. Now when this task gets to be over-laborious, the laborers are likely to go on strike. The grate, then, is not properly raked; clinkers form, and slowly the smothered fire glows dull and dies” (Curtis).

Even though no such dire fate overtakes one, the penalties of excessive proteid consumption are found in many ills, for which perhaps the victim seeks in vain a logical explanation; gastro-intestinal disturbance, indigestion, intestinal toxæmia, liver troubles, bilious attacks, gout, rheumatism, to say nothing of many other ailments, some more and some less serious, are associated with the habitual overeating of proteid food. But excessive food consumption is by no means confined to the proteid foodstuffs; general overfeeding is a widespread evil, the marks of which are to be detected on all sides, and in no uncertain fashion. One of the most common signs of excessive food consumption is the tendency toward obesity, a condition which is distinctly undesirable and may prove decidedly injurious. Undue accumulation of fat is not only a mechanical obstacle to the proper activity of the body as a whole, but it interferes with the freedom of movement of such muscular organs as the heart and stomach, thereby interposing obstacles to the normal action of these structures. Further, whenever undue fat formation is going on in the body, there is the ever present danger that the lifeless fat may replace the living protoplasm of the tissue cells and so give rise to a condition known as “fatty degeneration.” While a superabundance of fat in the body is a sure telltale of overeating, the absence of obesity is by no means an indication that excess of food is being avoided. There is here, in man as in animal kind, much idiosyncrasy; some persons, especially those endowed with a long and large frame, tend to keep thin even though they eat excessively, while others grow fat much more readily. As a well-known physician has expressed it, “In the one case, the subject burns, instantly and mercilessly, every stick of fuel delivered at his door, whether or not he needs the resulting hot fire roaring within, while the other, miser-like, hoards the rest in vast piles, filling the house from cellar to garret.”

Temperance in diet, like temperance in other matters, leads to good results, and our physiological evidence points out plainly, like a signpost all can read, that there is no demand on the part of the body for such quantities of food as custom and habit call for. Healthfulness and longevity are the prizes awarded for the successful pursuance of a temperate life, modelled in conformity with Nature’s laws. Intemperance, on the other hand, in diet as in other matters, is equally liable to be followed by disaster. A physician of many years’ experience, with opportunities for observation among different classes of people, has written, “that overeating tends to shrink the span of life in proportion as it expands the liver is demonstrable both directly and indirectly. Let any actuary of life-insurance be asked his experience with heavy-weight risks, where the waist measures more than the chest, and the long-drawn face of the businessman, at memory of lost dollars, will make answer without need of words. Then let be noted the physique of the blessed ones that attain to green old age, and, in nine cases out of ten, spry old boys—no disparagement, but all honor in the phrase—will be found to be modelled after the type of octogenarian Bryant or nonogenarian Bancroft—the whitefaced, wiry, and spare, as contrasted with the red-faced, the pursy, and the stout. It is true, as has already been mentioned, that in old age much of an adventitious obesity is absorbed and disappears, but the Bryant-Bancroft type is that of a subject who never has been fat at all. And just such is preëminently the type that rides easily past the fourscore mark, reins well in hand, and good for many another lap in the race of life.”[75]

With these thoughts before us, we may consider briefly just what is involved in these new dietary standards that aim to conform more closely with actual body needs. Referring at first to proteid food, it may be wise to again emphasize the fact that the weight of the body, i. e., the weight of the proteid-containing tissues, as contrasted with excessive fat accumulation, is one of the important factors not to be overlooked when determining the dietary needs of a given individual. As must be perfectly clear, from all that has been said, the man of 170 pounds’ body-weight has more proteid tissue to nourish than the man of 130 pounds’ weight, and consequently what will satisfy the requirements of the latter individual will not suffice for the former. We must understand distinctly that no general statement can be made applicable to mankind at large, but due consideration must be given to the size and weight of the individual structure. We have found that the average need for proteid food by adults is fully met by a daily metabolism equal to an exchange of 0.12 gram of nitrogen per kilogram of body-weight. This means a katabolism of three-fourths of a gram of proteid matter daily, per kilogram.

Remembering, however, that the intake of proteid food must be somewhat in excess of the actual proteid katabolism, since not all of the proteid of the food is available, and as this is a variable amount depending upon the proportion of animal and vegetable foods with their different degrees of digestibility and availability, we may place the required intake of proteid at 0.85 gram per kilogram of body-weight, still keeping to maximum figures for safety’s sake. Hence, for a man weighing 70 kilograms or 154 pounds, there would be required daily 59.5 grams—say 60 grams—of proteid food to meet the needs of the body. These are perfectly trustworthy figures, with a reasonable margin of safety, and carrying perfect assurance of being really more than sufficient to meet the true wants of the body; adequate to supply all physiological demands for reserve proteid, and able to cope with the erratic requirements of personal idiosyncrasies. It will be observed that such an intake of proteid food daily is equal to one-half the Voit standard for a man of this weight, while it is still further below the Atwater standard and far below the common practices of the majority of mankind in Europe and America, as indicated by the published dietary studies.

It may not be out of place to state at this point that in the writer’s opinion the use of the terms “standard diet” and “dietary standards,” etc., is objectionable, since such usage seems to demand a certain degree of definiteness in the daily diet for which there is no justification. As in the use of the term “normal diet,” there is danger of misinterpretation, and of the assumption that dietary habits should be regulated strictly in accord with certain set principles. This I believe to be altogether wrong; there should be, on the contrary, full latitude for individual freedom, but freedom governed by an intelligence that appreciates the significance of scientific fact and is willing to mould custom and habit into accord with them. What is needed to-day is not so much an acceptance of the view that man requires daily 0.85 gram of proteid per kilogram of body-weight, as a full appreciation of the general principle, which our definite figures have helped to work out, that the requirements of the body for proteid food are far below the customary habits of mankind, and that there is both economy and gain in various directions to be derived by following the general precepts which this view leads to. In other words, there is no advantage, but, on the contrary, much bother and worriment, in attempting to follow out in practice the details of our more or less exact physiological experiments.

The general teaching which they afford, however, can be adopted and put in practice in our daily lives, without striving to follow too closely the so-called standards which our experiments have led to. Again, the sample dietaries adopted in our experiments have no special virtue, aside from the general principle they teach that simple foods are quite adequate for the nourishment of the body, and that the amount of nitrogen or proteid they contain was sufficient to meet the demands of the particular individuals consuming it. Broadening intelligence on matters of food composition is called for on all sides, and as this is acquired together with due appreciation of the relative nutritive values of proteid, fat, and carbohydrate, there is placed at our command the power of intelligent discrimination, with the ability to apply the principles set forth in our own way, in harmony with personal likes and dislikes.

To the majority of us, not very familiar with the percentage composition of ordinary food materials, and unaccustomed to the weighing of food in grams, the figures given from time to time may have failed to convey a very definite impression regarding the actual amounts of the various foods made use of. Further, our ideas concerning the bulk of many of the common articles of food necessary to furnish the 60 grams of proteid required daily by a man of 70 kilograms body-weight may be somewhat hazy. The following table, however, will be of service in this direction: