Natural polyphenols-gut microbiota interactions and effects on glycolipid metabolism via polyphenols-gut-brain axis: A state-of-the-art review

Background: Natural polyphenols provide numerous human-health promoting benefits, including gut microbiota regulation, microbial composition changes, and improvement of glycolipid-related metabolic disorders and insulin resistance. In fact, about 90-95% of the ingested polyphenols will reach the colon to interact with gut microbiota. On the one hand, polyphenols and their microbial metabolites affect glycolipid metabolism by enhancing intestinal barrier protection and reducing blood glucose and lipid level. On the other hand, polyphenol and its microbial metabolites influence glycolipid metabolism via gut-brain axis.Scope and approach: This review focuses on the biotransformation of different types of polyphenols by gut microbiota and their metabolic pathways, as well as the mechanism of polyphenols or their microbial metabolites affecting glycolipid metabolism. The available evidence relating to natural polyphenols with different structures and sources as well as their metabolites produced by gut microbiota and the interaction between polyphenols and gut microbiota have been reported and discussed. Importantly, this review highlights the mechanism of polyphenols or their microbial metabolites affecting glycolipid metabolism via polyphenols-gut-brain axis.Key finding and conclusion: Polyphenols and their metabolites regulate blood glucose and lipid levels through the signaling pathways of inflammation-related factors, regulate glucose homeostasis, improve insulin resistance, reduce oxidative stress, and regulate the intestinal microbial composition. Besides, natural polyphenols affect glycolipid metabolism of the host via the gut-brain axis, including autonomic nervous system, neuroendocrine system, hypothalamic-pituitary-adrenal axis (HPA), and intestinal immune system pathways. It is still a challenging task to fully elucidate the mechanisms of the complex gut microbiota, and how different structural types of polyphenols and their metabolites regulate blood glucose and lipid levels.