Physiological Role of Gut Microbiota for Maintaining Human Health

Background: The human body is colonized by an extremely complex and abundant aggregation of microbes, collectively referred to as the gut microbiota. Recent studies have focused on the link between these microbes and our health. Summary: Diet contributes to shaping the gut microbial structure and influences metabolic functions of the host. Alteration of the microbial structure and function (dysbiosis) is associated with the pathogenesis of various disorders. Fermentation is the process by which anaerobic bacteria (Firmicutes and Bacteroidetes) break down indigestible carbohydrates to short-chain fatty acids (SCFAs; acetate, propionate and butyrate), collaborating with species specialized in oligosaccharide fermentation (e.g. Bifidobacteria). Butyrate and propionate can regulate intestinal physiology and immune function, while acetate acts as a substrate for lipogenesis and gluconeogenesis. The gut microbiota regulates immune homeostasis via the induction of regulatory T cells and Th17 cells. In addition, butyrate has strong anti-inflammatory effects possibly through the inhibition of histone deacetylase activity. Metabolic products generated by the gut microbiota, such as SCFAs, GABA, tryptophan, serotonin and catecholamine, transmit a signal to resident cells in the gut. Key Message: Advances made in the DNA sequencing technology and bioinformatics have revolutionized our understanding of the microbes in the gut.