> Phytoestrogens, natural plant compounds abundantly found in soy and soy products, behave as weak estrogen mimics or as antiestrogens. They are considered to be EDCs [endocrine disrupting compounds], and have some beneficial effects on health, including reducing the risk of breast cancer and improving metabolic parameters. However, the supporting evidence that consumption of phytoestrogens is beneficial is indirect and inconsistent. Lifetime exposure to estrogenic substances, especially during critical periods of development, has been associated with formation of malignancies and several anomalies of the reproductive systems.
Soy protein does blunt testosterone production. https://www.sciencedaily.com/releases/2013/10/131010091557.h...
Soy's effects are well known, at least among (some) doctors.
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edited after the parent's edit:
Soy contains phytoestrogens, which are endocrine disruptors. Soy is incredibly estrogenic (http://igrow.org/livestock/beef/hormones-in-beef-myth-vs.-fa... Table 1). See the following research if you're interested.
https://www.ncbi.nlm.nih.gov/pubmed/21175082
> Phytoestrogens, natural plant compounds abundantly found in soy and soy products, behave as weak estrogen mimics or as antiestrogens. They are considered to be EDCs [endocrine disrupting compounds], and have some beneficial effects on health, including reducing the risk of breast cancer and improving metabolic parameters. However, the supporting evidence that consumption of phytoestrogens is beneficial is indirect and inconsistent. Lifetime exposure to estrogenic substances, especially during critical periods of development, has been associated with formation of malignancies and several anomalies of the reproductive systems.
And, the most relevant one:
https://academic.oup.com/humrep/article/23/11/2584/2913898/S...
"These data suggest that higher intake of soy foods and soy isoflavones is associated with lower sperm concentration."