Protein in the Diet

For the past ten years the Health Organization of the League of Nations has been engaged in the study of nutrition in relation to public health. Reports on this work are now being published in the Quarterly Bulletin of the Health Organization. There is no doubt that nutrition is an important factor in any scheme of preventive medicine. It is not only a physiological but an economic problem.

Body Needs Determined

The requirements of the human body have been carefully analyzed, but it is to the protein element to which attention may here be directed. It has been found that the adult protein intake should never be below 1 gramme of protein intake should never be below 1 gramme of protein per kilogramme of body-weight. Moreover, the protein should be derived from a variety of sources, and a portion of it should certainly always be of animal origin. A study of the nutritive value of the various available protein is, therefore, necessary in this connection.

It is found on investigation that the natural foods all contain more or less proteins on the other hand are proteins. The pure proteins on the other hand are often incapable of sustaining the growth of the body or maintaining its nutrition. A pure protein such as gelatin comes within this category. Two common products are stated to consist of protein mixtures which are capable of providing for body maintenance, but do not permit of body growth.

These two protein mixtures are carrots and cocoa. It is pointed out that most of the studies carried out have been in connection with animals other than man, that is “on species in which development is swift.” It is, therefore, necessary to argue by analogy and comparison, that is from animals to man. “There is nothing to show that we are entitled to apply direct to man, without first introducing a coefficient of correction, quantitative data obtained on the other animal species.”

Most foods, by virtue of their mixed composition, satisfy both the energy requirements and the specific nitrogen requirements of the body. The nutritive value of a protein is stated to be the resultant of two factors. One of these is the proportion which gains access to the organism as a result of the process of digestion, while the other factor is the proportion of such materials taken in as is actually utilized by the body in satisfying its needs.

The findings are as follows: “Taken as a whole, animal proteins (meat, viscera, milk, eggs) are unquestionably superior to all vegetable proteins (cereals, legumes, green vegtables). The values of the former lie between 70 and 100, and those of the latter between 50 and 70. Must it be inferred from this that the former should, in some proportions at least, enter into the adult diet? By no means. The difference between one group and the other is much too small for nitrogen needs ever to remain unsatisfied as long as the food intake is adequate in the matter of energy yield; and this is true even of an unvaried and monotonous diet consisting of those foods which are quantitatively or qualitatively poor in proteins.”

This statement will prove very satisfactorily to vegetarians for it seems to prove that animal food is not absolutely essential or even necessary for the bodily maintenance. It may be pointed out however, it is not merely necessary to maintain the nitrogen equilibrium of the body in order to keep it in good health. We must supply more protein in the diet than that required to satisfy the specified nitrogen needs of the body. Probably, therefore, we require more than mere vegetable protein in order to accomplish this, unless we are to be compelled to partake of more vegetable material than the digestive organs can deal with without injuring them and upsetting digestion.

It is pointed out that the need for protein in man is always very small. Among the substances of animal origin, the superiority of the total proteins of milk is unquestionable. Unfortunately these prove to be quite indigestible in the case of some persons. The proteins of most viscera are equal to or superior to those of meat. There seems, too, to be a kind of synergic action achieved by combining various proteins in the diet, that is by supplementing a foodstuff which is poor in protein by one which contains more of this material.

It has been concluded that the “old dietary of the working and peasant classes of our country, of which bread, potatoes, legumes, green vegetables, fruit and milk products form the bulk, in which meat is rarely used, and then only as an appetizer, is the most reasonable of practices.” This is in closest accord with the rational guiding principles of modern physiological knowledge.

Small Amount of Meat Required

With meat the nitrogenous equilibrium is secured by a very small daily nitrogen intake. It is, therefore, not as all necessary for bodily requirements to consume much meat. In fact if too much meat is eaten, harmful effects usually result. So with milk, for it is a mistake to drink too much of it for the same reason. It is otherwise with bread and other cereal products. It is otherwise with bread and other cereal products. Their proteins possess a much lower biological values, and so much more must be eaten to secure the necessary nitrogenous equilibrium.

Here, again, one may suffer if too much bread is eaten. This is one of the reasons why a mixed diet is best, and why food “stunts,” of which milk and bread seem to be the most prominent at the present time, should be avoided. Our protein requirements in the diet are really very small. This fact is of fundamental importance, and should never be lost right of.

As regards the ability of food proteins to satisfy growth requirements. Professor Terroine of Strasburg has made some observations gained from feeding rats with a 10 per cent protein content in the diet over a period of 28 to 30 days. The foods used which such as could be partaken of by man. The figures arrived at express the weight increase in grammes per gramme of protein intake. Of food stuffs of vegetable origin, whole-grain barley heads the list with the figure of 1.2 to 1.9 Wheaten flour also investigated. Of these veal muscle gives that highest figure, namely, 3.88. Pig’s liver yields 3.54; beef muscle 3.15, and milk 2.89. As regards wheat Professor Terroine found that the total proteins (whole flour) are quite definitely superior to those remaining in the refined flour, with a miling yield of 74 per cent.

Protein Production in Man Less than Animals

He points out that, per unit of weight and of time, protein production is eleven times as great in the pig as in man, and eight times as great as in the rat. It would thus seem that, whereas in the case of man, requirements of growth scarcely count at all in his total needs, the inverse is true for both the pig and the rat. Thus measurements on other animal species, and especially on rats, cannot be applied to man without correction. Moreover, the distribution of the built-up proteins is substantially different. Professor Terroine readily admits these facts.

It has been definitely pointed out that “there is absolutely no advantage to be gained by increasing the protein intake above the amount necessary to meet total specific endogenous expenditure and the needs of protein production for growth,” Summing up the general principles which should govern the composition of the human diet throughout the period of growth, Professor Terroine maintains that the use of proteins for the satisfaction of energy requirements is to be deprecated.

An over-abundance of protein material is of no advantage to development, and may even prove harmful to it. Therefore, the basis of the diet should always consist of foods rich in carbohydrate material, especially cereals and after them potatoes. If these do not yield an adequate supply of protein, when they are given in quantities sufficient to fulfill energy requirements, then they should be supplemented either by substituting leguminous foods or by adding foods of animal origin. Of the latter he says that fresh skim-milk is by far the most economical, while amongst animal foods the viscera are cheap.

There is not doubt that this study of dietetic requirements is very helpful. At the present time the food of the working classes and of the poor fall far below the necessary requirements for the maintenance of nutrition and of health. If is not so much a case of expense as of the selection of the proper foodstuffs. A fresh herring costs less than a meat pie or sausages, or even tinned meat, and yet it contains as much, if not more, nourishment.

Oatmeal, a Nutritious Food

Oatmeal contains much nutrient material, a although it has recently been condemned as prejudicial to the preservation of children’s teeth. It is, however, not much in use amongst the poorer classes who prefer white bread. A thorough knowledge of the relative value of various foodstuffs is often of much advantage in practice. Meantime the Health Organization is doing good work which may bear much fruit if only their observations and conclusions are attentively studied by the public and by those engaged in the supply of foodstuffs.

Medical World (London)

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