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Why Does Soy Reduce Estrogen Levels In Studies?


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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’?

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Soy is widely known in health circles as pro-estrogenic and feminizing and men are recommended to avoid it.


Those assertions are widely  disputed.


See for example:

Soy and Health Update: Evaluation of the Clinical and Epidemiologic Literature  [November 2016]



16. Male Feminization  


Two case reports describing feminizing effects that allegedly occurred as a result of soyfood consumption have been published [389,390]. However, in both cases the individuals were said to have consumed 360 mg/day isoflavones (~9-fold greater than the mean intake among older Japanese men) in the context of unbalanced and likely nutrient-deficient diets since soyfoods accounted for the vast majority of calories consumed. Furthermore, in contrast to the rise in circulating estrogen levels noted in one case [389], no effects on estrogen levels have been noted in numerous clinical studies in which men were exposed to as much as 150 mg/day isoflavones [391].


Similarly, the drop in testosterone levels noted in the other case [390] is as already noted, inconsistent with the preponderance of the clinical data showing neither soy nor isoflavone supplements affect testosterone levels [283]. More specifically, a systematic review and meta-analysis that included 15 placebo-controlled treatment groups with baseline and ending measures and an additional 32 reports involving 36 treatment groups found no effects of soy protein or isoflavone intake on testosterone, sex hormone binding globulin, free testosterone or the free androgen index [283]. Studies published subsequent to this meta-analysis have reached similar conclusions [168,392,393,394]. The two aforementioned case reports simply illustrate that consuming excessive amounts of essentially any food can potentially lead to abnormalities [389,390].


The article is worth reading in its entirety.

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