Mode of Action
Isoflavones bind preferentially to the estrogen receptor and cause a weak estrogenic or anti-estrogenic effect
Soy isoflavones have a weak estrogenic hormone-like activity. Estrogens are signaling molecules that exert their effects by binding to estrogen receptors in cells. Soy isoflavones have a structural similarity to 17-β-estradiol and bind the same receptors. The estrogen-receptor complex interacts with DNA to modify the expression of estrogen-responsive genes.
Estrogen receptors are found in numerous tissues including reproductive tissues, bone, liver, heart, and brain. Soy isoflavones preferentially bind to estrogen receptor-β, mimicking the effects of estrogen in some tissues and blocking the effects of estrogen in others.
This estrogenic effect is dependent on the tissue. Anti-estrogenic effects of phytoestrogens in reproductive tissue could help reduce the risk of hormone-associated cancers (breast, uterine, and prostate), while estrogenic effects in other tissues could help maintain bone mineral density and improve blood lipid profiles. Soy isoflavones may alter the biological activity of endogenous estrogens and androgens by inhibiting the synthesis and activity of enzymes involved in estrogen metabolism.
Soy isoflavones and their metabolites also have biological activities that are unrelated to their interactions with estrogen receptors. For example, soy isoflavones can inhibit tyrosine kinases, enzymes that stimulate cell proliferation and thus are potential molecules of interest in anti-cancer research.