Soybeans. We've all seen it growing in the fields of Ontario, but soy-rich foods have traditionally been fairly absent from the Western diet. Asian diets, on the other hand, have typically been rich in soy products in the past, and it was always anecdotally noted that women from Asian countries suffered from much milder cases of menopause. The perceived reason behind this? Soy-based foods are rich in isoflavones, a major group of phytoestrogens. But can the addition of soy-rich foods to a woman's diet help their health in any other important ways? According to Dr. Wei Lu's research group from the Institute of Preventive Medicine in Shanghai, China, they most certainly can. Breast cancer recurrence and mortality, it would seem, are inversely associated with soy intake.

In research that was recently published in the Journal of the American Medical Association (302: 2437 - 2443), Dr. Lu and his colleagues undertook a massive population-based cohort study that followed 5042 female breast cancer survivors in China for a period of 4 years after their diagnosis. The numbers were quite staggering: the 4-year mortality rates were 10.3% versus 7.4% for women in the lowest versus the highest quartiles of soy protein intake, respectively. Similarly, the 4-year recurrence rates were 11.2% versus 8.0% for the same groups. These are not trivial differences.

Since I am not a cancer researcher, I was very surprised to see these results. The first question that popped into my head was simple: why had this not been tested for before (especially in a place like China, where soy intake is relatively high)? Shockingly, the in vitro effects of isoflavones had been noted by a couple of groups, and the results were the opposite of those shown here; namely, genistein (a major isoflavone), has been shown to enhance the proliferation of breast cancer cells (Inflammopharmacology 16: 219 - 226, 2008). Furthermore, several in vivo and in vitro studies have suggested that soy isoflavones may interact with tamoxifen (a very common chemotherapy drug), though both synergistic and antagonistic interactions have been demonstrated.

So what are we to make of all this? Until this point, no other large cohort studies had been performed to this magnitude to look at the role that soy may play in cancer recurrence. The results seem clear enough: among women with breast cancer, soy food consumption is associated with decreased risk of death and recurrence. Does this mean that soy is some sort of miracle food? Probably not. But maybe eating a soy burger instead of a fatty hamburger every once in a while wouldn't hurt. Not only would you be helping our local farmers, but you'll be helping yourself too.