What’s the deal with soy & breast cancer?

What’s the deal with soy & breast cancer?

Who has heard that soy is bad for women because they increase the risk of cancer due to their phytoestrogen levels? 🙋🏻‍♀️

This is actually NOT TRUE. On the contrary, soy has been found to be protective against breast cancer, reduces all-cause mortality in women with breast cancer, and reduces the risk of breast cancer recurrence in breast cancer survivors. 

In a recent meta-analysis of prospective cohort studies, soy/ soy product consumption was associated with cancer mortality including gastric, lung, and colorectal cancers. Women who consumed the highest intakes of soy isoflavones (which are isolated soy protein products) had a 10% lower risk of all-cause mortality compared to those with the least amount of soy. Furthermore, every 5g/d increase in soy isoflavones decreased breast cancer death by 12%!

So what is it about soy? The soy isoflavones are similar in structure to estradiol, a type of estrogen that is made in all of our bodies. The similarity means that the isoflavones are able to bind to the estrogen receptors in our body — but WAIT — isn’t this bad? The answer is NO  because fthe even though the isoflavones are similar to estradiol, they don’t have the same capacity to exert estrogenic effects. This means that their ability to bind onto those same receptors as estrodiol creates a competing environment and could potentially block the estrogenic effects that estradiol would’ve exerted if estradiol had binded. It is this mechanism  that is thought to be protective against breast cancer and what makes soy/ soy isoflavones safe in breast cancer patients. 

Particularly in postmenopausal women taking tamoxifen (an estrogen receptor modulator, meaning it reduces estrogenic activity in an environment with estrogen), soy intake has been shown to have a synergistic (cooperative) effect. Again, the hypothesis as to why these two components may be beneficial together is due to the mechanism explained above.

PMID: 31278047, PMID: 28263368, PMID: 19221874

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