It is beginning to be recognized by all students of nutrition that proteins from different sources may have unequal nutritional value. This is exhibited, for example, in the unlike efficiency of different proteins in sparing the body from a loss of tissue protein; it is likewise manifested by the striking differences in growth on diets alike in every respect except the character of the proteins they contain.
The reason for these biologic differences is now known to lie in the amino-acid content of the different proteins. Those albuminous compounds, which furnish the essential amino-acids in proportions approximating the ideal as determined by the body's synthetic needs, are most economical from the standpoint of nutrition. As a rule, though by no means in every instance, the proteins of meat, fish, eggs and milk exhibit a superior value as conservers of body protein when they are contrasted with the proteins of the