Biotransformation and Gut Microbiota-Mediated Bioactivity of Flavonols

Consumptionof fruits and vegetables has been associated with areduced risk of multiple diseases, such as metabolic disorders. Flavonolsare the most ubiquitous flavonoids in fruits and vegetables. However,dietary flavonols exhibit a general low oral bioavailability for theirextensive biotransformation mediated by phase II enzymes in enterocytesand liver as well as by microbiota in the gut lumen. In this context,flavonols have brought attention to a paradox between low bioavailabilityand health-promoting effects. Flavonols are often transformed priorto absorption, which could change their biological activity. Comparedto their parent compounds, the corresponding metabolites of flavonols in vivo might exhibit similar or higher intrinsic bioactivities,or perhaps a decreased efficacious effectiveness. Indeed, a growingbody of evidence from biological function studies of metabolites supportsthe positive and significant contribution of in vivo metabolic processes, particularly conversion mediated by gut microbiota,to the health-promoting benefits of flavonols. As such, further understandingof the metabolic fate of flavonols and biological activities of theirmetabolites as well as the possible impact of microbiota-mediatedconversion on the bioactivity is of great significance to guide arational diet with flavonol-rich fruits and vegetables and/or flavonol-containingfunctional foods.