The study. of the phenomena of nutrition is making rapid progress nowadays. So far as the rôle of the proteins is concerned, attention has become centered in the amino-acids as the fundamental food fragments with which all theories of nutrition must now be concerned.1 So long as it was still assumed that the proteins are absorbed in a form relatively like the original foodstuff — for example, as proteoses or complex polypeptids — the theory of their subsequent metabolism had to be framed somewhat differently from that suggested by the conclusions of the most recent writers who assume that a more complete disintegration takes place in the digestive tract. To say that we absorb our protein intake in the form of amino-acids is, however, a long way from explaining the subsequent stages by which the ingested nitrogen becomes a part of the tissues.
The latest studies of Van Slyke
WHAT BECOMES OF THE PROTEIN DIGESTION PRODUCTS?. JAMA. 1914;LXII(4):303-304. doi:10.1001/jama.1914.02560290053027