Therapeutic mechanisms of traditional Chinese medicine to improve metabolic diseases via the gut microbiota

Metabolic diseases such as obesity, type 2 diabetes mellitus, and hyperlipidemia are associated with the dysfunction of gut microbiota. Traditional Chinese medicines (TCMs) have shown considerable effects in the treatment of metabolic disorders by regulating the gut microbiota. However, the underlying mechanisms are unclear. Studies have shown that TCMs significantly affect glucose and lipid metabolism by modulating the gut microbiota, particularly mucin-degrading bacteria, bacteria with anti-inflammatory properties, lipopolysaccharide- and short-chain fatty acid (SCFA)-producing bacteria, and bacteria with bile-salt hydrolase activity. In this review, we explored potential mechanisms by which TCM improved metabolic disorders via regulating gut microbiota composition and functional structure. In particular, we focused on the protection of the intestinal barrier function, modulation of metabolic endotoxemia and inflammatory responses, regulation of the effects of SCFAs, modulation of the gut-brain axis, and regulation of bile acid metabolism and tryptophan metabolism as therapeutic mechanisms of TCMs in metabolic diseases.