Protein

Meat as a Food 

Meat is one of the most important foods. It is usually the item around which the balanced meal is built. In studying the composition and the chemical constituents of meat, the role it plays in the diet will be understood. 

Protein. 

Meat is undoubtedly the most widely used of all animal proteins. This use of meat as a source of protein is scientifically sound because of the high biological value of its protein. The belief is no longer held that proteins from whatever source are of equal value in the diet. 

Dr. H. H. Mitchell makes this point clear in the following statement: "Even vegetable foods such as dried (navy) beans and cocoa, which are relatively rich in crude protein are unimportant as sources of protein in nutrition because of the enormous losses of nitrogen in the course of their utilization in digestion, or in metabolism, or both. Their high content of protein is deceptive and the conclusion that such foods are 'meat substitutes/ though frequently stated, must be considered erroneous. "Among the animal foods it is evident that meats and meat products are preeminent as sources of protein. Although the biological value of animal tissue proteins (nitrogen) is appreciably lower than those of eggs or of milk, the higher content of protein in animal tissues, either on the fresh or dry basis, offsets or more than offsets their greater losses in metabolism.''1

McCollum and Simmonds emphasize the same point: "It is surprising that proteins of all peas and beans are of low biological value. This means that they are not well utilized when they form the sole source of protein in the diet. This fact compels a revision of views formerly held concerning the importance of seeds of the leguminous plants. A few years ago it was generally taught that peas and beans were excellent substitutes for meats. . . . Proteins from one source, rich in certain digestion products which were furnished in but small amounts by proteins from another source might be combined, and each protein would enhance the value of the other. Unfortunately, the proteins of peas, beans and soy beans do not enhance to any marked degree the quality of the cereal grain proteins. In this respect these proteins are distinctly inferior to meat proteins."2 

Dr. Casimer Funk and Dr. Benjamin Harrow make the following statement about the use of meat as protein food: "Meat is the most popular protein food, but at the same time contains other food constituents. We find proteins in peas, beans, and cereals, though as a rule the proteins found in the plant world are not as 'complete' as those found in the animal world. This is a strong argument against the adoption of a strictly vegetarian diet."3

A survey of Table 3 will disclose the marked superiority of animal foods over vegetable foods as sources of protein. Another angle from which protein study is approached is the supplementary relations which exist between proteins from different sources. Proteins with the same amino-acid deficiencies will not supplement each other. Proteins from meats are decidedly valuable in enhancing the proteins of the cereal grains. This is due not only to the fact that meats and cereal grains do not have the same amino-acid deficiencies but also to the fact that the proteins from both of these sources are highly assimilable. 

Fat. 

Fat is a valuable constituent of food. It is used in the body to form fatty tissue and to furnish energy. Fat has a greater fuel value than any other food constituent. One pound of fat will yield two and one-fourth times as much heat as do proteins or carbohydrates. Meats, especially the fat meats, such as bacon and salt pork, are splendid energy foods.

EARLY in the history of the science of nutrition meat was regarded just as one of the several protein foods. As knowledge of protein values increased greater stress was placed on the fact that animal proteins, namely, meat, milk, eggs, and cheese must be differentiated from vegetable proteins because of the higher biologic value of the former class of proteins. You learned this in Lesson One; also that meat is an excellent source of two essential minerals, iron and phosphorus; that meat contains copper; that meat furnishes energy; and that meat is a source of vitamins, especially the glandular tissue. Lesson Nine presents some of the more recent findings of research on the value of meat in the diet. 

Meat in the Normal Diet 

Protein requirement. 

The question of minimum and optimum protein intake has long been a battleground in the science of nutrition. There is a wide difference of opinion concerning the minimum amount of protein which will maintain health and vigor, although the higher protein standard is more generally accepted. The human race instinctively has chosen the high level of protein intake. Voit, a pioneer in the field, concluded from observation of the amount of protein taken by persons generally that 118 grams was the proper amount for the average man engaged in ordinary activities. Atwater advocated about the same amount, 120 grams. This estimate was generally accepted. 

Chittenden, from experiments on himself and a group of students and soldiers, concluded that the accepted protein intake was too high and that about 50 grams daily will assure the best results. McCollum favors a more liberal allowance and points out that Chittenden's experiment represented too short a part of the life span to be conclusive. Muller tells of the decrease in mental and body efficiency and decreased resistance to disease which was experienced in Germany during the war, when one of the chief characteristics of the war-time ration was protein deprivation. McLester sums up the discussion of the relative value of high and low protein diets: 

"Thus it would appear that the terms optimum and minimum as applied to diet are not synonymous, and that the smallest permissible intake is not necessarily the best. Meltzer understood this when he said that as an engineer adds the factor of safety when he builds a bridge, a similar factor should be added in the diet. We may be able to get along happily and well, at least for a time, on a minimal protein intake, but the diet which promises the greatest insurance against decay and disease is the one which carries with it a liberal factor of safety. This is the optimum diet. 

"It seems fair, then, to conclude that the earlier estimates of man's protein needs were approximately correct, and that to enjoy sustained vigor and to experience his normal expectancy, man must eat a liberal quantity of good protein. By liberal is meant an amount in excess of his theoretic needs, such an amount as the race, in its long experience, has instinctively chosen—say, 100 grams daily, more or less. By good is meant proteins of protein mixtures which are of high biologic value, in which the proteins of meat or milk, preferably both, find first place."*

Value of a mixed diet. 

The question of a mixed diet versus the vegetarian diet revolves around the amount and kind of protein which most adequately meets body needs. From earliest times man has thrived on a mixed diet. Nature has equipped him to do so. The kind of teeth and the nature of his digestive apparatus clearly indicate the suitability of a mixed diet. Regarding the value of a mixed diet, McCollum says: "In general, a vegetable diet will be markedly improved by the inclusion of muscle tissue meat, and more so by the addition of the glandular organs, but even these features of the subject are not from the standpoint of good nutrition the most important. It is scarcely practicable for man to eat enough leafy foods to enable him to succeed with the strictly vegetable diet. The limiting factor is the amount of leafy food which can be consumed."1 

Vegetarian diet. 

It is possible to live on a strictly vegetarian diet but it is not easy to do so and maintain the body in the highest degree of efficiency. It is often shown that the so-called vegetarian diet is supplemented with animal protein in the form of milk and eggs. McCollum says: "The diet which is strictly vegetarian will practically always be of relatively low protein content. The addition of even small amounts of meat, even of the muscle variety, will be very valuable when such a regimen is adhered to. Eggs, because of their relative richness in fat-soluble A and water-soluble B, will be even more effective supplements, and the same statement will apply to the consumption of small amounts of glandular tissue. Even small amounts of foods of animal origin will tend, therefore, to enhance the diet of one who is forced by economic reasons, rather than by ethical reasons, to subsist in the main upon vegetable foods. In another connection we shall present data showing that a diet too low in protein or in which the proteins are of a poor quality, exerts very deleterious effects upon experimental animals." 2 

The objection of vegetarians to a meat diet are not valid, as one writer points out: "History does not indicate that the eating of meat has the debasing effect, physical or moral as feared by them (vegetarians). The most vigorous, intellectual and highly civilized people the world has known have eaten meat."3

1 MCCOLLUM, E. V., The Newer Knowledge of Nutrition, 2nd edition. 

2  , The Newer Knowledge of Nutrition, 2nd edition.

3 MCLESTER, JAMES S. , Nutrition and Diet in Health and Disease.

The reducing diet. 

A nutrition problem of considerable importance has arisen with the present-day fashion for a slender figure. It is doubly essential that the restricted diet be well balanced. A very important consideration in the reducing diet is the preservation of nitrogen equilibrium. In reducing there should be no loss of body protein. The reducing diet should be low in caloric value but sufficiently high in protein to abundantly equal the body needs. In addition to a liberal supply of protein, the quality of the protein is important. Proteins of high biologic value are necessary. These are the proteins which supply all of the amino-acids in adequate amounts for building the body tissues. Such proteins are found in meat, milk, and eggs as supplements to the cereal grain proteins. Sometimes in planning the reducing diet, the satiety value of the foods included is entirely overlooked. This gives rise to an unsatisfied feeling which is reflected in the disposition of the person on the diet. On this point McLester says: 

"Other things being equal, the patient should be allowed to eat the food which in largest measure allays his hunger and which gives him the greatest degree of satisfaction. Meat has the highest satiety value of all foods; it 'sticks to the ribs' longest. Therefore, the protein that the patient receives should be largely in the form of meat. For the same reason, clear meat soups and broths are also useful; they have high satiety values without carrying much real nourishment."! 

It is obvious that reducing is not to be entered into carelessly and without competent medical advice and direction. The growing girl who chooses a reducing diet neither wisely nor well is taking grave chances with her future health. She runs the risk of so lowering her resistance that she is an easy prey to disease. McLester points out the necessity of viewing the protein intake from a clinical viewpoint. He says: "I have been impressed by the anemia shown by many patients who, from necessity or from a desire to become fashionably thin, have subjected themselves to rigid dietary restrictions. Animal experimentation has proved that a diet which contains liberal amounts of meats is the best blood builder, and one wonders whether an optimum protein intake is not, after all, a good insurance against disease. Clinical experience shows that it is."2 

Overweight may be due to an organic condition which only a physician can diagnose, and a physician's guidance in matters of diet is essential. Where there is no organic cause for overweight, rational diet should still be the rule.

Meat in the diet of the child. 

The growing child has a greater "protein requirement" than an adult, because of constantly building new tissue and wearing out old. There are the same good reasons for using meat as the source of protein in the diet of the child as in the diet of the grown-up. 

Liver is used with excellent results in child feeding. In the first place, the protein of liver is of high biologic value and it is relatively free from connective tissue; in the second place, it is a good source of vitamins; and in the third place, it is rich in iron. In regard to vitamins, liver is given as an excellent source of vitamins A and G; a good source of vitamin B; and vitamins C and D are present. Bacon, because it is so easily digested, is one of the first meats to be given to the very young child. In planning the diet of the child, it must be borne in mind that the "protein requirement" should be met with protein of high biologic value, and the animal proteins—meat, milk, cheese, and eggs—fall in this class. 

A publication from the Children's Bureau, United States Department of Labor, makes the following statement regarding meat in the diet of the pre-school child: 

"Meat and fish supply valuable proteins, minerals, and vitamins. At the beginning of the second year small servings of tender meat—beef, chicken, lamb, or liver, boiled, broiled, or roasted, and finely minced should be given at least three times a week. By the time the child is eighteen months old he may have meat or fish every day. As the child's ability to chew increases, he may be given larger pieces of meat, but it always must be tender. Veal, ham, or pork, properly cooked, may be given to the child over four."3 

Meat in reproduction and lactation. 

In recent animal experimentation4  it has been found that reproduction and lactation were improved by the addition of a meat supplement to a wheat-milk diet. The rate of growth and the general vigor of the young of the meat fed animals were greater than in the control group. Experiments of this nature are of considerable significance in human nutrition.