Dietary intake and bioavailability of polyphenols

The main dietary sources of polyphenols are reviewed, and the daily intake is calculated for a given diet containing some common fruits, vegetables an d beverages. Phenolic acids account for about one third of the total intake and flavonoids account for the remaining two thirds. The most abundant fla vonoids in the diet are flavanols (catechins plus proanthocyanidins), antho cyanins and their oxidation products. The main polyphenol dietary sources a re fruit and beverages (fruit juice, wine, tea, coffee, chocolate and beer) and, to a lesser extent vegetables, dry legumes and cereals. The total int ake is similar to 1 g/d. Large uncertainties remain due to the tack of comp rehensive data on the content of some of the main polyphenol classes in foo d. Bioavailability studies in humans are discussed. The maximum concentrati on in plasma rarely exceeds 1 mu M after the consumption of 10-100 mg of a single phenolic compound. However, the total plasma phenol concentration is probably higher due to the presence of metabolites formed in the body's ti ssues or by the colonic microflora. These metabolites are still largely unk nown and not accounted for, Both chemical and biochemical factors that affe ct the absorption and metabolism of polyphenols are reviewed, with particul ar emphasis on flavonoid glycosides. A better understanding of these factor s is essential to explain the large variations in bioavailability observed among polyphenols and among individuals.