Personalizing protein nourishment

Abstract

Proteins are not equally digestible-their proteolytic susceptibility varies by their source and processing method. Incomplete digestion increases colonic microbial protein fermentation (putrefaction), which produces toxic metabolites that can induce inflammation in vitro and have been associated with inflammation in vivo. Individual humans differ in protein digestive capacity based on phenotypes, particularly disease states. To avoid putrefaction-induced intestinal inflammation, protein sources, and processing methods must be tailored to the consumer's digestive capacity. This review explores how food processing techniques alter protein digestibility and examines how physiological conditions alter digestive capacity. Possible solutions to improving digestive function or matching low digestive capacity with more digestible protein sources are explored. Beyond the ileal digestibility measurements of protein digestibility, less invasive, quicker and cheaper techniques for monitoring the extent of protein digestion and fermentation are needed to personalize protein nourishment. Biomarkers of protein digestive capacity and efficiency can be identified with the toolsets of peptidomics, metabolomics, microbial sequencing and multiplexed protein analysis of fecal and urine samples. By monitoring individual protein digestive function, the protein component of diets can be tailored via protein source and processing selection to match individual needs to minimize colonic putrefaction and, thus, optimize gut health.

Keywords: Digestibility; predigestion; protease; putrefaction; supplementation.

Fig 1

Diagram of the effects of protein maldigestion and putrefaction in the gut. A) Healthy protein digestion: I. Dietary protein enters the stomach. II. Protein in the stomach stimulates G-cells secrete gastrin. III. Gastrin stimulates enterochromaffin-like (ECL) cells, which releases histamine that stimulates parietal cells. Gastrin also stimulates chief cells to release pepsinogen. IV. HCl denatures the proteins and activates pepsinogen into pepsin. Pepsin begins cleaving proteins into smaller peptides. V. Cholecystokinin (CCK) and secretin released by the small intestine and stimulates the pancreas to release digestive enzymes and HCO₃. VI. The pancreas releases HCO₃ and enzymes (trypsinogen, chymotrypsinogen, procarboxypeptidase, etc.). Enterokinase (released by intestinal cells) activates trypsin, and trypsin activates chymotrypsinogen and procarboxypeptidase. VII. Amino acids and di-and tripeptides get absorbed into the enterocytes primarily in the jejunum. VIII. Primarily carbohydrates reach the colon and undergo fermentation releasing vitamins and short-chain fatty acids (SCFA). B) Incomplete protein digestion and pathogenesis: I. Decreased HCl limits protein denaturation and pepsin activation. II. Pancreatitis and pancreatic insufficiency result in decreased secretion of digestive enzymes. III. Inflammation in the intestine can impair CCK release and thus lower pancreatic secretion of proteases. IV. Protein escapes digestion and reaches the colon, which can promote microbial putrefaction. Colonic putrefaction produces toxic metabolites such as hydrogen sulfide, ammonia and p-cresol.