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."*