Effects of Short Chain Fatty Acids Produced by the Gut Microbiota on Host Physiology: A Review of the Literature With Emphasis on Diseases Linked to the Gut Microbiota

The microbiome is the collection of all microorganisms living commensally, symbiotically, or pathogenically on a host. Microbiomes are found throughout the animal kingdom and can have mutually beneficial effects on host and microbes alike. In humans and other mammals, the largest collection of microorganisms is found in the GI tract, specifically the colon and small intestine. The gut microbiota has been shown to be shaped by many factors including health and diet. In turn, the composition of the gut microbiota has been shown to influence the state of health of its host. This effect has been linked to the production of certain metabolites. Specific metabolites considered to have a major impact on host physiology are known as short chain fatty acids (SCFA). These are metabolites produced from anaerobic fermentation of dietary fibre in the proximal and distal colon. Fermentative processes that breakdown complex, fibrous carbohydrates are aided by interactions among different bacterial phyla. These interactions are known as cross feeding, and the final products produced through the consecutive breakdown of fibrous molecules by fermentation are dependent on the relative abundances of these various microbial phyla. Research has shown that the composition of the gut microbiota is linked to the production of various amounts of SCFA metabolites that affect bodily functions. Functions include weight gain and inflammation, both of which have been linked to the development of diseases. This review presents an analysis of current literature related to the production of the SCFAs propionate, acetate, and butyrate in the gut, with emphasis placed on the effects that these metabolites have on host inflammatory and metabolic.