In conclusion, the facts here presented bearing on food requirements, especially those that relate to the need for proteid food, are seemingly harmonious in indicating that the physiological necessities of the body are fully met by a much more temperate use of food than is commonly practised. Dietary standards based on the habits and usages of prosperous communities are not in accord with the data furnished by exact physiological experimentation. Nitrogen equilibrium can be maintained on quantities of proteid food fully fifty per cent less than the every-day habits of mankind imply to be necessary, and this without increasing unduly the consumption of non-nitrogenous food. A daily metabolism of proteid matter equal to an exchange of 0.10–0.12 gram of nitrogen per kilogram of body-weight is quite adequate for physiological needs, provided a sufficient amount of non-nitrogenous foods—fats and carbohydrates—is taken to meet the energy requirements of the body.
The long-continued experiments on many individuals, representing different types and degrees of activity, all agree in indicating that equilibrium can be maintained indefinitely on these smaller quantities of food, and that health and strength can be equally well preserved, to say nothing of possible improvement. The lifelong experience of individuals and of communities affords sufficient corroborative evidence that there is perfect safety in a closer adherence to physiological needs in the nutrition of the body, and that these needs, so far as proteid food is concerned, are in harmony with the theory of an endogenous metabolism, or true tissue metabolism, in which the necessary proteid exchange is exceedingly limited in quantity. There are many suggestions of improvement in bodily health, of greater efficiency in working power, and of greater freedom from disease, in a system of dietetics which aims to meet the physiological needs of the body without undue waste of energy and unnecessary drain upon the functions of digestion, absorption, excretion, and metabolism in general; a system which recognizes that the smooth running of man’s bodily machinery calls for the exercise of reason and intelligence, and is not to be intrusted solely to the dictates of blind instinct or to the leadings of a capricious appetite.
CHAPTER VII
THE EFFECT OF LOW PROTEID DIET ON HIGH PROTEID ANIMALS
Topics: A wide variety of foods quite consistent with temperance in diet. Safety of low proteid standards considered. Arguments based on the alleged effects of low proteid diet on high proteid animals. Experiments of Immanuel Munk with dogs. Experiments of Rosenheim. Experiments of Jägerroos. Comments on the above experiments. The experiments of Watson and Hunter on rats. The writer’s experiments with dogs. Details of the results obtained with six dogs. Comparison of the results with those of previous investigators. Effect of a purely vegetable diet on dogs. Different nutritive value of specific proteids considered. Possible influence of difference in chemical constitution of individual proteids. Effect of low proteid diet on the absorption and utilization of food materials in the intestine of dogs. General conclusions from the results of experiments with animals.
Man is by choice an omnivorous creature; he reaches out ordinarily in all directions for as wide a variety of foods as his circumstances and surroundings will allow. He rightly cultivates a taste for foods that have individuality of flavor, and derives pleasure and satisfaction from the eating of delicacies that appeal to palate and to reason. All this he can do without becoming an epicure or a glutton, and without violation of physiological laws or disregard of the teachings of temperance. As a being endowed with reason and intelligence he is, however, necessarily mindful of the possible deleterious effect of undue quantities of food, as he is likewise mindful of the desirability of avoiding certain varieties of food which personal experience has taught him are fraught with possible danger. Care and prudence in diet are legitimate outcomes of a reasonable interest in the welfare of the body, upon which so largely depend the happiness and working power of the individual.
The adoption of dietary habits that aim to accord with the physiological requirements of the body does not compel a crucifying of the flesh or a disregard of personal likes and dislikes. A reasonable intelligence combined with a disposition to exercise the same degree of judgment and care in the nutrition of the body as is expended on other matters, of no greater importance, pertaining to the individual, to the household, or to business interests, are all that is needed to bring about harmony between every-day dietary habits and the nutritive requirements of the body. There is no occasion, unless one finds pleasure and satisfaction in so doing, to resort to a limited dietary of nuts and fruits, to become an ardent disciple of vegetarianism, to adopt a cereal diet, to abjure meats entirely, or to follow in an intensive fashion any particular dietary hobby, except so far as may be necessary to insure an adequate amount of non-nitrogenous foods to meet the energy requirements of the body without unduly increasing the intake of proteid or nitrogenous food. Naturally, a man leading a life of great physical activity with the consequent demand for a large energy-yielding intake will be compelled to resort largely to vegetable foods, rich in starch and poor in proteid, or to eat largely of fatty foods. Reliance on meats and animal foods in general, under such conditions, would plainly involve a high proteid intake with a consequent high nitrogen metabolism, with the chance that even then the energy requirement would not be fully met.
In view of all that has been said, reinforced by the various facts brought forward as evidence, we must recognize the value of the non-nitrogenous foods as a source of energy, and this means plainly food from the plant kingdom. In any rational diet, vegetable foods of low nitrogen-content must predominate, while animal foods with their higher nitrogen values must be greatly subordinate in amount, if the nitrogen or proteid metabolism of the body is to be maintained at a level commensurate with true physiological requirements. But there comes the ever-recurring question, Are the lower proteid standards quite safe to follow? Are we warranted in turning aside from the teachings based on the habits and customs of mankind? Many reasons have already been presented which seemingly justify an affirmative answer, while the experimental results and the observations on various groups of people, covering years of time, speak with no uncertainty regarding the element of safety, and indicate clearly that the absolute proteid requirement of the body is quite small; much smaller indeed than the amount of proteid food consumed by the average individual would seemingly imply.
Probably the most striking evidence, certainly of an experimental nature, so far presented against the safety of a relatively low proteid diet for man is that based on the results of several studies made to ascertain the effect of a reduced proteid intake on so-called high proteid animals. Animal kind may be divided into three groups according to the nature of their food, viz., high proteid feeders, such as carnivorous animals in general, of which the dog is a good type; omnivorous or moderate proteid consumers, to which class man belongs; and low proteid consumers, such as herbivorous animals. Three series of experiments have been reported by independent workers on the effects of reducing the amount of proteid food in the diet of dogs. The results of these experiments were of such a character that it has come to be understood that animals of this type cannot exist for any great length of time on a low proteid diet. It is affirmed that in a relatively short period the animals reach such a state that they either die, or are in such poor condition that they must be fed a more liberal amount of proteid to maintain them alive. The explanation offered is that the low proteid diet results “in a loss of the power of absorption from the intestinal tract, caused apparently by a change in the condition of the epithelial cells, as well as by a diminished secretion of the digestive juices.”
The argument based on this evidence is that while a high proteid animal feels at once, or almost immediately, the deleterious effect of a reduction in the amount of proteid food, an omnivorous animal may be more tardy in manifesting the injurious action, which, however, is sure to follow sooner or later from any material reduction of proteid below the customary standards. In other words, man as a moderate proteid consumer can endure for a time even large reductions in the amount of proteid food, but eventually there will be manifested some of the disastrous results obtained with dogs. Here, we have a somewhat serious indictment, one that merits careful consideration. To be sure, it may be objected that between dog and man there is a wide gulf, and that there is no justification for assuming that these two types of animal life have anything in common. Still, the experience of many years has taught the physiologist that much light can be thrown upon the processes of higher types of life by a study of what occurs in lower forms, and on the subject of nutrition any one of experience would hesitate to cast out of court the evidence gathered from observation of what occurs among the higher animals. It will be the part of wisdom, therefore, to scrutinize somewhat carefully the character of this evidence obtained from a study of the behavior of dogs toward a low proteid diet.