Isoflavones Made Simple – Genistein’s Agonist Activity for the Beta-Type Estrogen Receptor Mediates Their Health Benefits

The isoflavone phytochemicals in soy foods are often misleading refered to as “weak estrogens”. In fact, there are two types of estrogen receptors, ERalpha and ERbeta. ERalpha activity is responsible for the feminizing and pro-carcinogenic effects of estrogen, whereas ERbeta activity is not feminizing, and tends to oppose the cancer-promoting activity of ERalpha. When people ingest feasible amounts of soy foods, the blood levels of the free isoflavone genistein become just high enough to effectively activate ERbeta, but are too low to meaningfully activate ERalpha – that’s why soy foods don’t cause feminizing effects in men. Genistein’s ability to selectively activate ERbeta helps to explain reports that frequent soy ingestion is linked with lower rates of breast, prostate, and colon cancer, yet is not associated with the pro-thrombotic effects of oral estrogen. Postmenopausal women are relatively protected from kidney disease and heart failure; this protection appears to be mediated by ERbeta, and hence might be replicated with soy foods. ERbeta has a small favorable impact on bones and the endothelial lining of arteries, and hence soy foods may be modestly beneficial for bone and vascular health, although they have less impact in this regard than hormonal estrogens. In short, regular ingestion of soy isoflavones appears to offer meaningful protection from several common cancers, and to provide some of the health benefits associated with estrogen activity, without the major risks.

Published in Medical Hypotheses 2006;1093-114.

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