Book description (Wiley): Consumer interest in the health benefits of many phenolic compounds found in plant foods and derivatives has grown considerably in recent years, giving rise to an increased demand for functional foods. Although preclinical and observational studies have promoted the protective properties of polyphenols for a range of chronic diseases, evidence has shown that most dietary polyphenols have little bioavailability. Once ingested, most of them are metabolized by either the intestinal enzymes or by the gut microbiota and then undergo extensive phase-II metabolism reaching significant concentrations of conjugated metabolites. They remain in the systemic circulation and target systemic tissues where trigger biological effects. The polyphenol-derived metabolites produced in humans are dependent upon the composition of the gut microbiota and the subject genetics. Thus all the metabolites do not show the same biological activity in different individuals. To fully understand the health effects of polyphenols, further clinical investigations are required.