Protein is man's chief source of nitrogen. The quality and quantity of dietary protein influence growth, maintenance and repair as well as reproduction and lactation. Furthermore, like carbohydrate and fat, protein is an important source of energy. In view of the indispensable part which it plays in vital processes, a recent review1 of the relationship between this nutritive substance and health and disease merits comment.
Man can adapt himself to varying amounts of protein in the diet; the material may be largely animal or vegetable in origin. Apparently harmful defects do not result from either extreme, provided the process of amino acid supplementation is effective and the total amount ingested is adequate. The nutritive value of proteins from different sources, to be sure, varies considerably, owing particularly to differences in their amino acid composition, some proteins containing all of the so-called indispensable amino acids, others lacking one or more.