Protein Digestion and Absorption

ALTHOUGH protein accounts for only about 11 to 14 per cent of the total calories that Americans ingest each day, this food substance is essential for nutritional homeostasis. The bulk of protein, which maintains nitrogen balance, is from exogenous sources, but endogenous protein is also important for nitrogen balance; from 25 to 200 g per day are presented to the small intestine in the form of enzymes, secreted proteins, secreted glycoproteins and desquamated epithelial cells. Only 2 to 5 per cent of the protein in contact with the absorbing surface of the small bowel escapes transport. Thus, the processes of . . .