Microbiota revolution: How gut microbes regulate our lives

Figure 2 The metabolic activity by the colonic microbiota. The intestinal microbiota finds an environment rich in polysaccharides which are not digested by stomach enzymes. Fermentation of polysaccharides by intestinal bacteria leads to the production of acetate, butyrate, and propionate, which are used as a carbon source by intestinal mucosal cells. The initial fermentation of the carbohydrate that escaped digestion in the small intestine is followed by the utilization and cross-distribution of metabolites by various members of the microbiota, and then the synthesis of short-chain fatty acids (butyrate, propionate, acetate). Proteolytic fermentation differs from saccharolytic fermentation because it releases many potentially toxic nitrogen and sulfur metabolites, such as ammonia, amines, nitrates, nitrites, and hydrogen sulfide[32,40].