Metabolic and colonic microbiota transformation may enhance the bioactivities of dietary polyphenols

Epidemiological evidences throughout the years have indicated that consumption of phytochemicals may play important functions in the regulation of pathological and normal biological processes. Polyphenols are one of the large and ubiquitous groups of phytochemicals. Dietary polyphenols are naturally present in a wide variety of fruits and vegetables, and potentially contribute to the maintenance of human health. However, growing information has indicated that the bioactive compounds from polyphenols may exert beneficial effects in part by their metabolites. The bioactive metabolites were converted by the gut microflora, liver microsomes and hepatocytes, and identified in intestinal, plasma, feces, and urine after dietary ingestion. Surprisingly, recent studies suggested that many metabolites possess more active biological functions than their precursors. In order to explore the possibilities of metabolites in food bioactive compounds, more clear understanding of the metabolic pathways and the molecular targets responsible for health promotion and diseases prevention are needed. In this review, we first summarize the distribution and beneficial health activities of metabolites from dietary polyphenols. We also discuss the available evidence on the relationship between metabolites bioefficacy and bioavailability of their parent polyphenol compounds. We hope that this knowledge will lead to future research to discover and develop new bioactive compounds as possible chemopreventive agents.