Intake, Bioavailability, and Metabolisms of Plant Polyphenols in Humans

Abstract

The total intake of plant polyphenols in humans is ca. 1 g/day, a major part accounts for flavonoids and phenolic acids. The main polyphenol dietary sources are beverages (tea, coffee, wine, fruit juice) and fruits. There is a great uncertainty in the intake of several classes of plant polyphenols, such as oligomeric proanthocyanidins and phenolic acids. The intestinal absorption of polyphenols is probably high, but the plasma concentration of the parent polyphenol is low. A majority of polyphenols is subject to hydrolysis in digestive tract and is then metabolized by the colonic microflora largely to phenolic acids, which can be also absorbed. After absorption, polyphenols and their metabolites are further bound in tissues. These transformations lead to a number of metabolites, which mostly retain the antioxidant activity.