The truth about SOY
Okay, everyone. I've been thinking about this topic for a while now and I'm so glad that I'm able to squeak this post out just under the (under) wire before Breast Cancer Awareness month comes to a close and Halloween festivities ensue tomorrow! A recent conversation I had with a colleague who asked about my opinion on soy led me to some incredibly eye-opening research that I wanted...no NEEDED...to SHOUT FROM THE ROOFTOPS or at least post and let as many people know as possible.
SOY has gotten a bad rap due to the longstanding notion that it may contribute to estrogen-related breast cancer risk. You see, soy contains substances called isoflavones, which are phytoestrogens. Phytoestrogens in soy have a very similar molecular structure to that of human estrogens which led to the THEORY that they bind to the SAME estrogen receptors on breast cancer cells which, in turn, causes those cells to multiply rapidly. Since we know that high levels of estrogen are linked to increased risk of breast cancer (in fact, 80% of all breast cancers are estrogen-sensitive), there have been concerns that these soy isoflavones can contribute to a higher risk developing breast cancer.
So, for decades, doctors and dieticians warned patients about the risk of consuming soy products - soy milk, soybeans (edamame), tofu, tempeh, etc.
However, a 2013 meta-analysis (read: compilation of multiple studies) where researchers looked at data from 22 studies on Asian women, who consume soy to a larger degree than Western cultures, showed that those that consumed the most soy had a 32% lower risk of breast cancer observed for both pre- and post-menopausal breast cancers. A 2014 meta-analysis reached similar conclusions. Wait, what? Why had I not ever heard of this? Instead, healthcare providers, myself included back when I was in clinical practice, were telling women to stop eating soy and to stop giving it to their boys (remember that?)!!! Heck, even I've said that to friends and always winced a little when I saw my also-plant-based husband throw tofu into his stir-fry.
When I went to review the literature (which is why this post took so long to write), I found studies dating way back to 2009 saying the SAME THING. Soy foods actually had an inverse relation to breast cancer risk (PMID: 19996398).
So, you may wonder, does soy play any role in breast cancer. YES, but is a good one!
First, a little estrogen 101...
There are different types of estrogen made in our bodies (mostly women, but to a small degree, men also synthesize estrogen). There are different types based on your age:
estrone - post-menopausal estrogen made predominantly by fat tissue
estradiol - pre-menopausal estrogen made predominantly by the ovaries
Not only do we have different types of estrogen in our bodies, we also have different kinds of estrogen receptors. Receptors are little docks where the estrogen molecule will attach to on the cell and thus begins a cascade of cellular events. There are the alpha receptors that I like to think of the 'accelerator' receptor can promote the growth of breast cancer cells. The beta receptors or "brake" receptors has a slowing down effect of estrogen by blocking cell growth that is part of the cancer process.
Estrogen synthesized in humans, particularly estrone (postmenopausal), binds to the alpha receptors. Soy isoflavones bind to the BETA receptors so while they look like estrogen, they bind to the receptor that SLOWS the growth of cancer cells. So, that's why soy foods with phytoestrogens can actually help REDUCE CANCER RISK.
So, please, if you'd like, enjoy soy :)