The composition of some proteins is widely dissimilar from those of body proteins. Consequently, the body in using the simpler parts into which these foodstuff proteins are broken up in digestion will have to discard surplus simple building materials.
As would be expected, the proteins in milk, which has as its function the provision of the necessary materials for the growth of the very young children, have high value involving little waste in their conversion to body proteins.
The proteins in milk products such as condensed, evaporated, and dried milks, and the various cheeses. In the case of cheeses, the process of manufacture breaks down some of the proteins, also in other ways varies their value and that of other constituents in cheese.
Consequently, cheese, though a thoroughly valuable protein foodstuff for adults, has its limitations with very young human beings. Nearly all nutritional foodstuff contain protein, but some of them only a small proportion. These, of course, would not be included in protein foodstuffs.
What foods have the most protein?
Lean meat is almost entirely protein of high value. Similarly fish is almost entirely protein. Peas, beans, lettuce, and other greens contain quantities of proteins which differ somewhat from animal proteins like those of meat and milk.
They do not show the same high protein economy in conversion into human proteins. But these vegetable foodstuffs have other most valuable compensating characteristics, such as their mineral and vitamin content.
The proteins from eggs have a high value in nutrition, since they are designed for the actual formation of a complete being within the shell. The proteins of milk, meat and eggs are all of the most valuable type, and are a desirable feature in any well arranged diet.
Cereals like wheat, oats, barley and rye contain lower quantities of proteins, which are of only moderate efficiency when used by themselves. The proteins from vegetables generally, like pumpkins, potatoes, carrots, and parsnips, blend well with those of milk, meat, and eggs.