Since it is essential to supply protein in the diet in adequate quantity and quality in order to sustain life, the study of protein foods is of vital importance.
The questions of how much protein a healthy individual requires, how much of this protein requirement must be supplied by proteins of animal origin, and the relative values of animal versus vegetable proteins, are age-old questions—questions that are of specific interest to the vegetarian, and of more than ordinary interest to all in times of food shortage or rationing.
Interesting and practical aspects of this protein problem have been studied recently. The preliminary report of the study has been given by Doctors Stare and Thorn in the American Journal of Public Health for December, 1943, pages 1444-1450. Specifically this study was concerned with (I) protein requirement of healthy adults ; (2) how much of this protein should be animal protein; and (3) the effect of exercise on the protein requirement.
This research was conducted by studying the dietary protein in relation to the physical efficiency of twenty-four physically normal young men who continued their usual daily activities. The men were divided into three groups of eight men each. The control group continued to eat the usual dietary, which, by the standards of the Food and Nutrition Board of the National Research Council, was good and provided an average of too grams of protein a day.
The low protein group subsisted on a diet from which "all meat, eggs, fish, nuts, legumes, cheese, and almost all milk were excluded. Their diet consisted essentially of cereal products, potatoes, other vegetables, fruit products, and oleomargarine, with not over four ounces of milk and cream a day." The high protein group were instructed to replace low protein foods with foods rich in protein, such as meat, milk, cheese, eggs; nut products, and legumes.
Each of the men was subjected to (I ) a thorough medical examination at the beginning and the close of the experiment; (2) complete blood studies, including serum protein and nonprotein nitrogen determinations ; (3) a routine examination of the urine and weekly estimation of nitrogen in a twenty-four-hour urine specimen: (4)weighing and evaluation of all food eaten: (5) estimation of the daily caloric expenditure in work done, by a daily hour-by-hour diary of each individual's activities ; (6) a weekly assessment of general physical fitness for hard work by the "pack test,'- which is a standardized exercise-tolerance test designed by the Harvard Fatigue Laboratory.
The average daily protein intake of the low protein group was about 50 grams, of which not more than 5 grams was in the form of animal protein. The normal or control group averaged too grams of protein, of which about 60 grams was animal protein. The high protein group averaged a daily protein intake of about 16o grams, mostly animal protein. Following are the essential features of this highly interesting and valuable research, which we feel will be of more than ordinary interest to readers of THE MINISTRY:
"No members of the low protein group, not even the hardest worker, who averaged about 5,500 calories expenditure on a working day, suffered measurable deterioration in physical vigor. The only symptom that could be attributed to the low protein diet was voiced by the two hardest workers, one a farmer and the other a man engaged in hard work in the woods. These men usually felt quite hungry about II A. m. and 4 A.m. Nevertheless, their day's work did not suffer from the low protein diet. No significant changes were found in serum albumin or globulin of the low protein group. In view of Chittenden's finding that a low protein diet is, in fact, beneficial to physical vigor and efficiency, it may be mentioned that the physical fitness of the subjects on the low protein diet was no better than that of the control or high protein groups. In the high protein group no measurable benefit to physical fitness from this large amount of protein could be observed in two months. No significant change was found in the serum albumin or globulin.
"Thus, throughout a period of two months, no measurable influence, either deleterious or beneficial, was seen in the physical vigor or efficiency in daily work of healthy young men subsisting on a diet providing 5o grams of protein, of which not more than 5 grams was animal protein. Likewise no beneficial or deleterious effect was observed in two months from a diet providing 160 grams of protein, most of which was animal protein. One should emphasize that both these diets were adequate with respect to calories and that a yeast concentrate was provided daily to the low protein group to ensure an excess of vitamins of the B complex.
"It seems reasonable to conclude from this experiment that a daily protein intake of so grams, of which as little as 5 grams consists of animal protein, is perfectly adequate for good health and efficiency, provided, and this is a most important proviso, the diet is adequate in other respects, particularly calories and thiamine. In addition, confirmatory evidence is offered that exercise, or hard manual labor, does not increase the protein requirement.
"This experinient should not be interpreted as implying that protein requirements of the normal adult can safely be reduced to so grams per day, of which only 10 per cent need be animal protein—not unless the diet is adequate in other respects. In dealing with the health of the public it is no doubt safer to rely on a protein level of at least 70 grams per day for the average adult man, and 6o grams per day for the aver, age adult woman as recommended by the Food and Nutrition Board. . . .
"Have present wartime food conditions in this country posed special problems with respect to protein foods and the health of the people? It is our belief that the answer to this question is definitely No. True, certain protein foods are rationed and others may be rationed, but as long as this country has access to a plentiful supply of calories, and a variety of whole-grain cereals and legumes, it is most unlikely that impairment of health from protein deficiency will ever occur. But there are very definite economic problems, as evidenced recently by the plentiful amount of livestock on the Western ranges and the amounts of meat available at consumers' markets. And there are definite psychological problems of convincing a population used to eating a high protein diet that one of much lower protein content, and low in animal protein, will not necessarily impair health. Lumberjacks may demand plenty of red meat to get timber cut, but that demand rests on habit and not on a nutritional or medical basis."
H. M. W.
