Research is currently divided over the effects of soy consumption on breast cancer. Some studies support the consumption of soy products for their preventive effects against breast cancer. For example, a follow up study conducted in Takayama, Japan supported the beneficial effects of consuming soy products. The population-based prospective cohort study sent self-administered questionnaires to 31,552 people living in Takayama, and the questionnaire had questions about alcohol use, smoking, physical activity, medical history, the age of menarche (first menstrual period), whether or not menopause had occurred, diet, BMI, etc. A 169 food item semi-quantitative food frequency questionnaire was also administered to subjects in the study, and nine types of soy food items were included within the questionnaire. The prevalence of cancer in Takayama was assessed through two regional population-based cancer registries. The results of the study showed that post menopausal women who consumed high quantities of soy products had significantly lower risks of breast cancer. There were not any significant associations between the consumption of soy products among pre menopausal women. Although the results of this study showed inverse associations between the consumption of soy products and breast cancer risk, there are a few problems with the study. One major concern is that the food frequency questionnaire was self administered, so there was most likely bias between the amount of soy products the subjects actually consumed and what they wrote on the questionnaire. Another concern is the study only provided associations between the consumption of soy products and breast cancer risk, and association does not equate to causation.
The protective effects of soy products and breast cancer for pre and postmenopausal women may only be seen in studies conducted on women in Asian countries according to a meta-analysis of published in Plos One. This meta-analysis of epidemiological studies analyzed 31 studies conducted on the association between soy intake and breast cancer risk in premenopausal women and 31 studies conducted on postmenopausal women. The premenopausal studies included 17 studies completed in Asian countries supporting the inverse association between breast cancer risk and soy consumption, and 14 of the studies conducted in Western countries did not have any statistically significant association between the consumption of soy and breast cancer risk. The results were similar for studies conducted on postmenopausal women. The studies conducted in Asian countries showed that there were statistically significant associations between the consumption of soy products and breast cancer risk while the majority of the studies conducted in Western countries had slightly significant inverse associations between breast cancer risk and soy consumption. One study conducted on breast cancer patients revealed concerns over the consumption of soy. 140 women who had early stages of breast cancer were provided with soy supplementation or a placebo from their cancer diagnosis until their surgery (between 7 and 30 days). Blood samples and tissue samples were taken from the women on the day of their surgery for analysis of gene expression and plasma genistein (a soy isoflavone) levels. The women also completed food frequency questionnaires to determine their consumption of soy products. The results of the study revealed that women who were give soy supplementation had statistically significant increases tumor gene expression from high plasma levels of genistein. Albeit the study suggested that soy products may induce increases in tumor gene expression, it was not conducted on women who did not have breast cancer, so these effects may only be seen in women who already have breast cancer. While studies remain inconclusive on the effects of soy consumption and breast cancer, I do not believe moderate levels of soy intake will increase or decrease the risk of a woman having breast cancer.
- Getz, Lindsey. “Soyfoods & Cancer.” Today’s Dietitian. Great Valley Publishing Company, Apr. 2013. Web. 15 Mar. 2016.
- Wada, Keiko, Kozue Nakamura, Yuya Tamai, Michiko Tsuji, Toshiaki Kawachi, Akihiro Hori, Naoharu Takeyama, Shinobu Tanabashi, Shogen Matsushita, Naoki Tokimitsu, and Chisato Nagata. “Soy Isoflavone Intake and Breast Cancer Risk in Japan: From the Takayama Study.” International Journal of Cancer Int. J. Cancer4 (2013): 952-60. Web. 15 Mar. 2016.
- Chen, Meinan, Yanhua Rao, Yi Zheng, Shiqing Wei, Ye Li, Tong Guo, and Ping Yin. “Association between Soy Isoflavone Intake and Breast Cancer Risk for Pre- and Post-Menopausal Women: A Meta-Analysis of Epidemiological Studies.” PLoS ONE2 (2014): n. pag. Web. 15 Mar. 2016.
- Kang, X., Q. Zhang, S. Wang, X. Huang, and S. Jin. “Effect of Soy Isoflavones on Breast Cancer Recurrence and Death for Patients Receiving Adjuvant Endocrine Therapy.” Canadian Medical Association Journal17 (2010): 1857-862. Web. 15 Mar. 2016.
- Shike, M., A. S. Doane, L. Russo, R. Cabal, J. Reis-Filo, W. Gerald, H. Cody, R. Khanin, J. Bromberg, and L. Norton. “The Effects of Soy Supplementation on Gene Expression in Breast Cancer: A Randomized Placebo-Controlled Study.” JNCI Journal of the National Cancer Institute9 (2014): n. pag. Web. 15 Mar. 2016.