Good news in breast cancer
The misinformation concerning soy and breast cancer has reached urban legend status; it is widely believed, but utterly false.
Unlike most urban legends, however, the erroneous belief that soy products promote breast cancer has dire consequences. It is time to stop telling women concerned about breast cancer to avoid soy products. In fact, health care providers should be advising more soy and other plant foods high in flavonoids in order to reduce the incidence of breast cancer.
Just a few years ago, I advised my patients with breast cancer that the direct data on soy and breast cancer was not yet available. I would then discuss my bias that soy probably did not promote breast cancer based on information from areas in Southeastern Asia where people ate the most soy. The incidence of breast cancer was not higher, as one would expect if soy promoted breast cancer, but tended to be lower than in areas of Asia where people consumed less soy.
I also suspected that the source for the soy concern was the usual "trumped up" defense of the status quo industries that compete with soy products. (See Big Tobacco Tactics in my December 2 blog)
I would leave it with patients that while I was not convinced that soy increased the risk for breast cancer, the jury was still out. In retrospect, I wish I had been more adamant in my support of soy, but I felt the data was still equivocal.
However, concrete data on soy is now available. The jury has returned, and without a reasonable doubt, soy is not guilty.
In a December 2009 issue of the Journal of the American Medical Association, a prospective study of over 5000 women in Shanghai with a history of breast cancer was reported. The women who ate more soy protein had fewer deaths or recurrences than those who ate less. This was true whether the breast cancer was estrogen positive or not and also whether the women were taking tamoxifen or not. The conclusion of the study was clear: "Among women with breast cancer, soy food consumption was significantly associated with decreased risk of death and recurrence."
The data supporting soy is not only from Asia. A definitive 2008 editorial in the British Journal of Cancer, Soy intake and breast cancer: elucidation of an unanswered question, outlines the data which not only clearly absolves soy in the promotion of breast cancer, but also builds a convincing case that soy is protective against the development as well as the recurrence of breast cancer. The protective effect was particularly noticeable for women who had a high level of soy intake during adolescence.
Urban legends do not die easily - the myth that soy is bad in breast cancer is unlikely to go away soon. Please join me in the crusade against breast cancer and help spread the real truth about soy.