A friend recently asked me if too much soy intake could be harmful. After all, soy contains precursors to estrogen production, and elevated estrogen has been implicated to varying degrees in the risk of heart disease and breast cancer.
My initial inclination was to think that soy intake should be fine. Even if soy were converted to estrogen in meaningful amounts, the body has remarkable feedback mechanisms. As estrogen levels rise, they feedback and shut off the the hormones that spur production in the first place. Still, I wasn’t sure, so I did a little research.
It turns out that, not only does soy not seem to raise estrogen levels, nutrients in soy might even protect against breast cancer (they cause cells to have normal life cycles with appropriate cell death, the opposite of cancer). Additionally, soy intake is associated with slight lowering of LDL (bad cholesterol) by about 5% and raising of HDL (good cholesterol) by about 3%. These changes are not huge, but they are probably enough to be clinically relevant, and regardless, they certainly suggest health benefits rather than any harm.
So the answer is . . . soy seems great. It’s not only ‘not harmful,’ it appears to have real health benefits. Enjoy!
sources: Journal of the American College of Nutrition: 2011 Apr;30(2):79-91: Soy protein effects on serum lipoproteins: a quality assessment and meta-analysis of randomized, controlled studies. Genes and Nutrition: 2012 Aug 3., PMID: 22864686: The soybean peptide lunasin promotes apoptosis of mammary epithelial cells via induction of tumor suppressor PTEN: similarities and distinct actions from soy isoflavone genistein.; Asian Pacific Journal of Cancer Prevention 2012;13(2):479-82: Positive effects of soy isoflavone food on survival of breast cancer patients in China; European Journal of Clinical Nutrition 2012 Sep;66(9):1044-9. doi: 10.1038/ejcn.2012.71. Epub 2012 Jun 20: Urinary estrogen metabolites in two soy trials with premenopausal women