title: Bacteria, colonic fermentation, and gastrointestinal health.
abstract: The colonic microbiota plays an important role in human digestive physiology and makes a significant contribution to homeostasis in the large bowel. The microbiome probably comprises thousands of different bacterial species. The principal metabolic activities of colonic microorganisms are associated with carbohydrate and protein digestion. Nutrients of dietary and host origin support the growth of intestinal organisms. Short-chain fatty acids (SCFAs), predominantly acetate, propionate, and butyrate, are the principal metabolites generated during the catabolism of carbohydrates and proteins. In contrast, protein digestion yields a greater diversity of end products, including SCFAs, amines, phenols, indoles, thiols, CO2, H2, and H2S, many of which have toxic properties. The majority of SCFAs are absorbed from the gut and metabolized in various body tissues, making a relatively small but significant contribution to the body's daily energy requirements. Carbohydrate fermentation is, for the most part, a beneficial process in the large gut, because the growth of saccharolytic bacteria stimulates their requirements for toxic products associated with putrefaction, for incorporation into cellular proteins, thereby protecting the host. However, as digestive materials move along the gut, carbohydrates become depleted, which may be linked to the increased prevalence of colonic disease in the distal bowel.
authors.affiliation: University of Dundee, Ninewells Hospital Medical School, Microbiology and Gut Biology Group, Dundee DD1 9SY, United Kingdom.
authors.forename: George T
authors.initials: GT
authors.lastname: Macfarlane
authors.forename: Sandra
authors.initials: S
authors.lastname: Macfarlane
mesh_terms: D000596:Amino Acids / Q000378:metabolism; D002087:Butyrates / Q000378:metabolism; D003106:Colon / Q000382:microbiology / Q000502:physiology; D003110:Colonic Neoplasms / Q000209:etiology / Q000378:metabolism; D004040:Dietary Carbohydrates / Q000378:metabolism; D004044:Dietary Proteins / Q000378:metabolism; D005232:Fatty Acids, Volatile / Q000032:analysis / Q000378:metabolism / Q000502:physiology; D005285:Fermentation; D005516:Food Microbiology; D041981:Gastrointestinal Tract / Q000382:microbiology* / Q000502:physiology*; D006262:Health; D006801:Humans; D006859:Hydrogen / Q000378:metabolism; D019344:Lactic Acid / Q000096:biosynthesis; D018384:Oxidative Stress; D011422:Propionates / Q000378:metabolism; D059748:Proteolysis
chemical_list: D000596:Amino Acids; D002087:Butyrates; D004040:Dietary Carbohydrates; D004044:Dietary Proteins; D005232:Fatty Acids, Volatile; D011422:Propionates; D019344:Lactic Acid; D006859:Hydrogen