ABSTRACT
Phytoestrogens are plant compounds that can bind to the mammalian estrogen receptor, and they have a wide range of biological effects. Phytoestrogens include isoflavones, coumestans, other bioflavonoids, lignans, and phytosterols, which occur in food in much higher amounts than steroid hormones. The finding that enterolactone, enterodiol, and equol are predominantly conjugated to glucuronic acid in portal venous blood suggests that conjugation of phytoestrogens may occur in the intestinal wall during absorption from the gut. Most studies of the metabolism of phytoestrogens have focused on their urinary excretion. The metabolism of flavonoids is known to proceed to metabolites like phenolic acids and resorcinols that do not have an intact flavone skeleton. The studies on isoflavone metabolism have been focused on reductive metabolism of soy isoflavones daidzein and genistein. Classical pharmacokinetics of isoflavones have established that the volume of distribution in adults is large, indicating a wide tissue distribution.
