Dr Siamak Adibi writes about how the stomach digests protein using stomach acid.
Intestinal phase of protein assimilation in man
Adibi, S. A. (1976). Intestinal phase of protein assimilation in man. The American Journal of Clinical Nutrition, 29(2), 205–215.doi:10.1093/ajcn/29.2.205
The importance of dietary proteins to opt imal nutrition and health is well recognized. Digestion and absorption which are necessary for utilization of amino acid constituents of these proteins are quite complex. The initial step in protein digestion is the gastric phase: dietary proteins are denatured in the acidic environment of the stomach. Denaturation renders dietary protein a more suitable substrate for the action of proteolytic enzymes. Although the in vivo digestion of protein in human stomach has not been extensively studied, it is generally assumed that it is minimal (1). In contrast, digestion by pancreatic proteolytic enzymes is considered to be critical in the assimilation of dietary protein. Pancreatic resection or insufficiency results in both a considerable decrease in the intraduodenal hydrolysis of protein (2) and an increase in fecal nitrogen (1). Intraluminal digestion produces free amino acids and small oligopeptides (3, 4). This review examines the protein source and the intestinal fate of these free amino acids and oligopeptides in