Food sources rich in polyphenols include onion, apple, tea, red wine, red grapes, grape juice, strawberries, raspberries, blueberries, cranberries, and certain nuts. 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 non-flavonoids and flavonoids. The flavonoids quercetin and catechins are the most extensively studied polyphenols relative to absorption and metabolism. The following are commonly proposed mechanisms by which phytonutrients may protect human health.
More research is needed to firmly establish the mechanisms of action of the various phytochemicals.
Listed below are a few selected population studies from the literature linking fruit and vegetable consumption to health. Journal of the American Medical Association. The differences in vegetable consumption between high and low intake rankings was not striking. Consumption of tomato products has been linked to decreased risk of prostate cancer. Journal of the American Medical Association.