 Soy foods have become controversial in recent years, even among health professionals exacerbated by misinformation found on the internet. Chief among the misconceptions is that soy foods promote breast cancer because they contain a class of phytoestrogen compounds called acoflavones. Since estrogens can promote breast cancer growth, it's natural to assume phytoestrogens might, too, but people don't realize there are two types of estrogen receptors in the body, alpha and beta. Unlike actual estrogens, soy phytoestrogens preferentially bind to and activate estrogen receptor beta. This distinction is important because the two types of receptors have different tissue distributions and often function differently and sometimes in opposite ways. And this appears to be the case in the breast, where beta activation has an anti-estrogenic effect inhibiting the growth-promoting effects of actual estrogen. Having we've known for more than 10 years, there's no excuse anymore. Effects of estradiol, the primary human estrogen, on breast cells are completely opposite to those of soy, phytoestrogens, which have anti-proliferative effects on breast cancer cells, even at the low concentrations one gets in one's bloodstream eating just a few servings of soy. Which makes sense, given that after eating a cup of soy means the levels in our blood cause significant beta receptor activation. So where did this outdated notion that soy could increase breast cancer risk come from? The concern was based largely on research that showed that the main soy phytoestrogen genestine stimulates the growth of mammary tumors in a type of mouse, but it turns out we're not actually mice. We metabolize soy isoflavones very differently from rodents. The same soy leads to 20 to 150 times higher levels in the bloodstream of rodents. The breast cancer mouse in question was 58 times higher. So if you ate 58 cups of soybeans a day, you could get some significant alpha activation too, but thankfully we're not hairless atomic over-reacted mice, and we don't tend to eat 58 cups of soybeans a day. At just a few servings of soy a day, with the excess beta activation we would assume soy would actively help prevent breast cancer, and indeed soy intake during childhood. Adolescents and adult life were each associated with a decreased risk of breast cancer. Those women who ate the most soy in their youth appear to grow up to have less than half the risk. This may help explain why breast cancer rates are so much higher here than in Asia, yet when Asians come over to the US to start eating and living like Americans, their risk shoots right up. For example, women in Connecticut, way up the top of the breast cancer risk, keep in their 50s, have like 10 times more breast cancer than women in their 50s living in Japan, but it's not just genetics. Since when they move here, their breast cancer rates go up generation after generation as they assimilate into our culture. Are the anti-estrogenic effects of soy foods enough to actually change the course of the disease? We didn't know until the first human study on soy food intake and breast cancer survival was published in 2009 in the Journal of the American Medical Association, suggesting that among women with breast cancer, soy food consumption was significantly associated with decreased risk of death and breast cancer recurrence, followed by another study, and then another, all with similar findings. That was enough for the American Cancer Society, who brought together a wide range of cancer experts to offer nutrition guidelines for cancer survivors, concluding that if anything, soy foods should be beneficial, and since then, two additional studies have been published for a total of 5, and they all point in the same direction, 5 out of 5 tracking more than 10,000 breast cancer patients. Pooling all the results, soy food intake after breast cancer diagnosis was associated with reduced mortality, meaning a longer lifespan and reduced recurrence, so less likely the cancer comes back. Anyone who says otherwise hasn't cracked a journal open in seven years. And this improved survival was for both women with estrogen receptor negative tumors and estrogen receptor positive tumors, and for both younger women and for older women, pass the edamame.