169. Relative Efficiency Of Different Proteins

The relative efficiency of protein according to its source is one of importance. Have vegetable proteins as large constructive value as those of animal origin? Is a larger proportion of the proteins of milk and meat available for the building of animal tissue than when derived from the cereal grains? We have seen that the "building stones" of animal proteins differ materially in proportion from those of vegetable proteins. Abderhaldenl calls attention in the following table to the much larger proportion of glutamic acid in the proteins of plant origin as related to their value for constructive purposes: 1 "Phys. Chemistiy," 1908, p. 653. See Note, p. 199.

These figures indicate that flesh foods are relatively more economical for tissue formation than vegetable foods. The proteins of flesh foods are themselves like the proteins that must be built into the animal body, and it seems plausible that their building stones can be used with less waste than can proteins of quite unlike constitution.

Von Noorden,1 an authority of note, estimates that sucklings are able to convert 90 per cent of food protein into body protein, but suggests that the proteins of milk are particularly well adapted to reconstitution.

The same author also suggests on theoretical grounds that, in general,2 "no more than 80 grams of body protein could be formed from 100 grams of protein in the food." This whole question must for the present be considered on a theoretical basis, but, at the same time, we are justified in believing that 1 "a given quantity of protein in the food cannot yield an equal amount of body protein, and also that animal proteins are more efficient in this respect than vegetable proteins."

1 "Metabolism and Practical Medicine," Von Noorden, Vol. I, p. 71. 2 Loc. cit., p. 70.