Soy based foods for estrogen receptor positive cancers

Hi all,

I recently asked a question to the cancer nutritional expert on Livestrong.  I thought the question and answer may be interesting to those of us with estrogen receptor positive cancers.

My question:

I had an estrogen receptor positive cancer. While my oncologist has not weighed in on this, I have heard many people say that I should stay away from soy products. As a vegetarian, I do rely upon soy products for my protein and I know how good they are for your diet generally. Is there definitive knowledge that eating soy products could be dangerous for those of us with estrogen receptor positive cancers?

The answer:

Melissa Mouton

Hi! Great question. I get this one alot! No, there is not definitive evidence that eating soy is dangerous for those with estrogen receptor positive (or negative) cancers. In fact, the evidence points more towards a protective role of soy with regards to breast cancer (other estrogen sensitive cancer such as ovarian have not been studied as much with regards to soy). Overall, the research is not yet clear, but much of the controversy surrounding soy intake has stemmed from a couple of old in-vitro (test-tube) studies that demonstrated estrogenic activity when isolated soy protein (a very processed product added to some food products like energy bars) was added to breast tissue cells in the laboratory. Based on these limited studies, it became common for physicians to recommend that their breast cancer patients avoid soy intake of any kind. More recent studies have been conducted taking a look at actual breast cancer patients and have suggested that soy intake may play more of a protective role in breast cancer survival. In addition to those studies, it is worth noting that population based studies indicate an inverse relationship with soy intake and breast cancer risk. For example, populations that have higher whole soy food intake tend to have lower risk of breast (and prostate) cancer. Some researchers have proposed the mechanism for this may be the binding of soy isoflavones (considered “weak” estrogens) to estrogen receptors in breast tissue, which blocks the binding of human estrogen to the receptors and thereby preventing the adverse stimulation of these receptors. Until more research is available, several major cancer treatment centers recommend breast cancer patients avoid extremely high intake of soy products and if desired choose a moderate amount of whole soy foods (such as edamame, tempeh, tofu) versus processed soy products. Moderate intake is considered 2 to 3 servings per day. References: Wu, A. H., Yu, M. C., Tseng, C. C., & Pike, M. C. (2008). Epidemiology of soy exposures and breast cancer risk. Journal of Breast Cancer, 98, 9-14. Shu, X. O., Zheng, Y., Cai, H., Gu, K., Chen, Z., Zheng, W., & Lu, W. (2009). Soy food intake and breast cancer survival. The Journal of the American Medial Association, 302(22), 2437-2443. Kang, X., Zhang, Q., Wang, S., Huang, X., & Jin, S. (2010). Effect of soy isoflavones on breast cancer recurrence and death for patients receiving adjuvant endocrine therapy. Canadian Medical Association Journal, 182(17), 1857-1862. Magee, P. J., & Rowland, I. (2012). Soy products in the management of breast cancer. Current Opinion in Clinical Nutrition and Metabolic Care, 15(6), 586-591. Nechuta, S. J., Caan, B. J., Chen, W. Y., Lu, W., Chen, Z., Kwan, M. L., Flatt, S. W., Zheng, Y., Zheng, W., Pierece, J. P., & Shu, X. O. (2012). Soy food intake after diagnosis of breast cancer and survival: an in-depth analysis of combined evidence from cohort studies of US and Chinese women. Nutrition and Cancer, 64(5), 652-665. Kang, H. B., Zhang, Y. F., Yang, J. D., & Lu, K. L. (2012). Study on soy isoflavone consumption and risk of breast cancer and survival. Asian Pacific Journal of Cancer Prevention, 13(3), 995-998. Zhang, Y. F., Kang, H. B., Li, B. L., Zhang, R. M. (2012). Positive effects of soy isoflavone food on survival of breast cancer patients in China. Asian Pacific Journal of Cancer Prevention, 13(2), 479-482. MD Anderson Cancer Center. (2013). A healthier diet for cancer survivors. Retrieved from http://www2.mdanderson.org/cancerwise/2013/08/healthier-diet-for-cancer-survivors.htmlDana-Farber Cancer Institute. (2011). Is eating soy safe for breast cancer patients and survivors? Retrieved from http://www.dana-farber.org/Newsroom/News-Releases/Is-eating-soy-safe-for-breast-cancer-patients-and-survivors-.aspxSeattle Cancer Care Alliance. (2013). Women’s Wellness Clinic Newsletter. Safe to enjoy soy. Retrieved from http://www.seattlecca.org/client/WWC_Newsletter_Summer-2013-FINAL-web.pdf

Best,

Clementine