• Dr Meltzer

Soy Products & Breast Cancer: Do They Increase or Decrease My Risk?

As part of Breast Cancer Awareness Month, let’s revisit a common question as it relates to soy products and breast cancer. You can also join us for a Free Educational Webinar on the Future of Breast Cancer Awareness to get any other questions you may have answered regarding breast cancer prevention.



Soy products can play a healthy role in your nutritional program–particularly as part of a plant-based, high-fiber, low saturated fat, phytonutrient-rich, antioxidant-rich, alkaline, chemical-free nutritional plan.

Are soy products good for your health or do they increase your risk for disease? Do soy products protect against breast cancer or increase your risk for breast cancer?


In the last few years there has been a lot of information in the media questioning the safety of soy. Let me address a few of these concerns, particularly as it relates to breast cancer. First off, it’s important to note that soy can be a staple to a healthy diet and has been show to help prevent a wide variety of chronic illnesses such as heart disease, osteoporosis, and many cancers–including breast, colon, and prostate cancer.[i],[ii],[iii] When you take a closer look at the nutritional profile of soy, it makes sense. Soy is a high-quality, alkaline protein source. It is also rich in fiber, phytonutrients, and antioxidants, all of which play an important role in protecting the body from long-term illness. With that in mind, let’s take a quick look at the benefits of soy, and then we can discuss the concerns that people have regarding soy and breast cancer.


The Benefits of Soy


There are two main benefits of consuming soy products as it relates to breast cancer. To begin with, many epidemiological and clinical research studies have found that soy products help reduce the risk of breast cancer.[iv] For example, a recent study in 2008 at the University of Southern California found that women who consumed an average of one cup of soymilk or ½ a cup of tofu a day had a 30% lower risk of developing breast cancer, relative to women who consumed little or no soy products.[v] Not only is this study consistent with a well established and growing body of scientific documentation showing soy’s protective effect on breast cancer, but it’s also consistent with my clinical observation in evaluating the nutritional profile of nearly 40,000 female patients in my career. It’s important to note, however, that the protective effect of soy products on breast cancer have been most notable in individuals who consume soy products earlier on in life and in adolescence, as breast tissue is forming.[vi],[vii]


The second benefit of soy is that it has been shown to reduce the risk of breast cancer recurrence for those previously diagnosed with breast cancer. For example, a study in the Journal of the American Medical Association–following over 5,000 women previously diagnosed with breast cancer–showed that women who regularly consumed soy milk, tofu, or edamame had a 32 % lower risk of recurrence and a 29% reduced risk of death.[viii]


Why Do Some People Believe Soy is Unsafe?

Despite the clinical research that suggests otherwise, it’s common to hear from time to time that soy products may be unsafe as it relates to breast cancer. So what is it that people are concerned about? The concern is typically around the isoflavones, also known as phytoestrogens, that are found in soy. Since increased estrogen levels in the blood have been associated with higher levels of breast cancer, some people have speculated that the plant-based estrogens (phytoestrogens) in soy might increase the risk of breast cancer as well. At the surface, it sounds like a reasonable theory. However, when you take a closer look at the science, this theory doesn’t hold up.


Interestingly enough, the impact of the phytoestrogens is just the opposite. Phytoestrogens, which are significantly weaker than human estrogen, have been shown to inhibit estrogen’s effects on the body when estrogens levels are high.[ix] What happens is the phytoestrogens can attach to the body’s estrogen receptor cells, and block endogenous and exogenous estrogen from attaching. Endogenous estrogen is human estrogen produced by the body. Exogenous estrogen is synthetic estrogen that can come from hormone replacement therapy or from exposure to synthetic chemicals–such as pesticides and heavy metals that make their way into our food supply–that have estrogen-like effects on the body.


I like to tell my patients that it’s kind of like a game of musical chairs. When the music stops, and someone is already sitting in your chair, there is nowhere for you to sit. In this case, the phytoestrogens are already sitting on the estrogen receptor sites, and keep the more harmful estrogen from attaching. In this way, the phytoestrogens can protect the body against high levels of endogenous and exogenous estrogen in the blood stream. This is one of the mechanisms by which many researchers believe soy products and the phytoestrogens in soy reduce the risk for breast cancer.


In Summary


So what’s my overall recommendation on soy? Soy products can play a healthy role in your nutritional program–particularly as part of a plant-based, high-fiber, low saturated fat, phytonutrient-rich, antioxidant-rich, alkaline, chemical-free nutritional plan. My clinical observations are consistent with epidemiological studies & clinical research that show that soy can help prevent breast cancer as well as reduce the risk of other long-term illnesses such as prostate cancer, heart disease, and osteoporosis. Keep in mind, when choosing soy products, be sure to emphasize organic, non-GMO, minimally processed soy. For example, tofu, soy milk, and soy yogurt, as well as fermented soy products such as tempeh, natto, and miso are all great options for including soy in your diet. Products that are heavily processed, commercialized, and filled with soy-protein isolate–such as some of the fake meat soy products–are probably not your best dietary sources of soy.


Looking for further information on soy and your health? For those that are interested, I like to refer to my patients to a great article put together by PCRM (Physicians Committee for Responsible Medicine), which elaborates on some of the studies referred to in this article and further discusses the topic of soy and your long-term wellbeing. You can access this article at http://pcrm.org/search/?cid=145

[i] Badger, T. M., Ronis, M. J., Simmen, R., & Simmen, F. A. (2005). Soy protein isolate and protection against cancer. Journal of the American College of Nutrition , 146S-149S.

[ii] Pipe, E. A., Gobert, C. P., Capes, S. E., Darlington, G. A., Lampe, J. W., & Duncan, A. M. (2009). Soy protein reduces serum LDL cholesterol and the LDL cholesterol:HDL cholesterol and apolipoprotein B:apolipoprotein A-I ratios in adults with type 2 diabetes. The Journal of Nutrition , 1700-1706.

[iii] Koh, W. P., Wu, A. H., Wang, R., Ang, L. W., Heng, D., Yuan, J. M., et al. (2009). Gender-specific associations between soy and risk of hip fracture in the Singapore Chinese Health Study. American Journal of Epidemiology , 901-909.

[iv]Badger, T. M., Ronis, M. J., Simmen, R., & Simmen, F. A. (2005). Soy protein isolate and protection against cancer. Journal of the American College of Nutrition , 146S-149S.

[v] Wu, A. H., Yu, M. C., Tseng, C. C., & Pike, M. C. (2008). Epidemiology of soy exposures and breast cancer risk. British Journal of Cancer , 9-14

[vi] Korde, L. A., Wu, A. H., Fears, T., Nomura, A. M., West, D. W., Kolonel, L. N., et al. (2009). Childhood soy intake and breast cancer risk in Asian American women. Cancer Epidemiology, Biomarkers & Prevention , 1050-1059.

[vii] Shu, X. O., Jin, F., Dai, Q., Wen, W., Potter, J. D., Kushi, L. H., et al. (2001). Soyfood intake during adolescence and subsequent risk of breast cancer among Chinese women. Cancer Epidemiology, Biomarkers & Prevention , 483-488.

[viii] Shu, X. O., Zheng, Y., Cai, H., Gu, K., Chen, Z., Zheng, W., et al. (2009). Soy food intake and breast cancer survival. JAMA: the Journal of the American Medical Association , 2437-2443.

[ix] Wiseman, H., O’Reilly, J. D., Adlercreutz, H., Mallet, A. I., Bowey, E. A., Rowland, I. R., et al. (2000). Isoflavone phytoestrogens consumed in soy decrease F(2)-isoprostane concentrations and increase resistance of low-density lipoprotein to oxidation in humans. The American Journal of Clinical Nutrition , 395-400.


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