How are dietary polyphenols metabolised?
At the beginning of the project, relatively little was known about the uptake of dietary flavonoids, their mechanisms of transport and metabolism, or the forms in which they exist in human plasma. As a direct result of Polybind, many of these outstanding issues have been clarified, and we are close to a definitive account of the bioavailability of quercetin and its derivatives in human foods. The joint discovery by several Polybind participants that flavonol glycosides bind to the intestinal glucose transporter and modify its activity, raised important questions relating to the effect of dietary flavonoids on the absorption and metabolism of other nutrients. We have firmly established that although the naturally occurring food-borne quercetin glucosides are absorbed from foods much more readily than free aglycones, the glycosides are not present in plasma of human subjects, even immediately after a test meal of onions rich in flavonoid glucosides. The major circulating compounds in hum
