About Polyphenols
Polyphenolic compounds are natural components of a wide variety of plants; they are also known as secondary plant metabolites. Food sources rich in polyphenols include onion, apple, tea, red wine, red grapes, grape juice, strawberries, raspberries, blueberries, cranberries, and certain nuts. The average polyphenol/ flavonoid intake in the U.S. has not been determined with precision, in large part, because there is presently no U.S. national food database for these compounds (USDA scientists and their colleagues are in the process of developing a database for foods rich in polyphenols). It has been estimated that in the Dutch diet a subset of flavonoids (flavonols and flavones) provide 23 milligrams per day. Earlier estimates of dietary intake that approximated 650 milligrams per day (Kuhnau, World Review of Nutrition and Dietetics, 1976; vol 24: pp 117) are generally thought to be too high as the estimate was based on data that were generated by "old" (less specific) methodology. Scientists at the Food Composition Laboratory, Beltsville Human Nutrition Research Center are currently developing new methodology for the accurate measurement of polyphenols in foods.
Polyphenols can be classified as nonflavonoids and flavonoids. The flavonoids quercetin and catechins are the most extensively studied polyphenols relative to absorption and metabolism.
