Bioaccessible unabsorbed polyphenols may play a role in the protection of the GI tract against RONS prior to their fecal excretion. In contrast to native polyphenols, less data exists on the antioxidant activity of bioavailable polyphenol phase II metabolites (conjugated derivatives). Despite the variable and overall relatively poor bioavailability of polyphenols (concentrations range between high nanomolar and low micromolar in human plasma and organs), polyphenols have been reported to be more efficient than vitamin C, vitamin E and carotenoids (concentration ranges between high micromolar and low millimolar in human plasma and organs) against oxidative stress at tissue levels.
