Why Does Soy Reduce Estrogen Levels In Studies?
Soy is widely known in health circles as pro-estrogenic and feminizing and men are recommended to avoid it. If that’s actually the case, can anyone explain why serum estrogen levels actually decrease in soy-supplemented groups in studies in both men and women? And why is there an inverse relationship between hormone dependent cancers such as breast and prostate cancer (I suppose all cancers are hormone dependent) and soy consumption? Here are just some of the studies I’m talking about:
https://www.ncbi.nlm.nih.gov/pubmed/8770469 - 36-oz of daily soymilk consumption for a month significantly decreased serum 17 beta-estradiol levels in premenopausal women.
https://www.ncbi.nlm.nih.gov/pubmed/9839524 - Estrone and estradiol levels were decreased by 23% and 27% at the end of the study in the soy milk supplemented group in Japanese women. The change in estrone and estradiol levels was minor in the control, non-soy group.
https://www.ncbi.nlm.nih.gov/pubmed/11303585 - Serum estrone concentrations decreased in the soy-supplemented group in Japanese men. There was no change in testosterone levels in both the soy group and the control group.
Is it that the estrogen circulation in blood decreases from soy but estrogen level inside the cell increases? Is that why soy is so widely considered as ‘estrogenic’?
Comments
"Serum estrogen levels decrease in soy-supplemented groups in studies in both men and women" because soybeans are a significant source of Daidzein and Genistein, which are plant phytoestrogens that are (if I am not mistaken) similar enough in structure to mammalian estrogens that they serve as mild SERMs, attaching themselves to estrogen receptors, which in turn prevents actual estrogens from doing so.
The "studies" you're referring to demonstrate a decrease in net serum estrogens because the consumption of soy products was controlled - set to relatively low amounts, such that the soy product(s) constituted a relatively small part of their diet.
When the intake of soy increases past a certain point, i.e. vegans consuming several glasses of soymilk, pounds of tofu, edamame, and especially soy protein isolate (present in numerous "fake meat" products, as well as vegan/vegetarian protein powders), it's a different story altogether
Isoflavone-rich soy protein isolate suppresses androgen receptor expression without altering estrogen receptor-beta expression or serum hormonal profiles in men at high risk of prostate cancer:
https://www.ncbi.nlm.nih.gov/pubmed/17585029
Soy protein isolate increases urinary estrogens and the ratio of 2:16alpha-hydroxyestrone in men at high risk of prostate cancer:
https://www.ncbi.nlm.nih.gov/pubmed/17885008
Here's a compilation of around 60 years' worth of studies on the harmful effects of soy isoflavones:
https://www.westonaprice.org/health-topics/soy-alert/studies-showing-adverse-effects-of-isoflavones-1950-2010/
It may well be that soy products can offer some small increase in serum testosterone when consumed in VERY small amounts. There's also no conclusive evidence suggesting that soy has an overtly FEMINIZING (estrogenic) effect. But there are some pretty good studies (see above) demonstrating an ANTI-ANDROGENIC effect, among other adverse health effects.