The digestion and absorption of protein by normal man

The work to be described in this paper was under- taken as a prelude to investigations on the digestion and absorption of protein in various clinical condi- tions, particularly those relating to diseases of the intestine. Although a large amount of work has been done on protein absorption in the last 50 years, there is still uncertainty about several important points, such as the nature of the di- gestion products absorbed by the mucosa or the time required for enzymic hydrolysis and actual absorption (see It appeared to us that 15N-labelled protein might, with advantage, be used in such studies. [15N]-Amino acids, [15N]ammonia and [15N]urea have been used in man, especially by Rittenberg and his colleagues (e.g.