Does Soy Protect Against or Promote Cancer?

By Dr. Sharon Gurm BSc, ND, Naturopathic Physician, Clinic Founder & Clinical Director

Conflicting evidence over the years makes it difficult for one to know – should I consume soy or not? Having extensively reviewed most of the literature, the answer is: it really depends on the individual. Research has shown that women who consumed soy during their early years (adolescence and early adulthood) had a reduced risk of developing pre-menopausal hormone dependant cancers such as breast and ovarian cancer. This is likely due to the “phytoestrogenic” (plant estrogen) activity of soy. Soy isoflavones (namely, genistein and daidzein) bind to and weakly activate estrogen receptors (such as those present on tissue cells of bones, breasts and ovaries), which may displace some of the stronger estrogen that our bodies produce and that we get from environmental exposures and animal food consumption. Because of this action, less harmful estrogen activity during the earlier years of hormone activity exerts a beneficial and cancer-protective effect.

A recently published prospective cohort trial of postmenopausal women with a history of breast cancer found that those who consumed the highest amount of soy who were concurrently taking tamoxifen (a drug commonly used for adjuvant hormonal therapy in estrogen positive breast cancer) had a lower risk of cancer recurrence. However, the group of postmenopausal women with a history of breast cancer who consumed the highest amount of soy and were not on tamoxifen experienced an increased risk of cancer recurrence.

I often give the following advice to most of my patients: consume 3-6 servings a week of soy, preferably in its ‘whole food’ form – i.e. soybeans, miso or tempeh. Soymilk is a great dairy alternative and high in calcium and cardio-protective healthy omega fatty acids. Purchase organic, non-GMO soymilk and consume 1-2 cups daily unless you have a known soy allergy or intolerance (some have a difficult time digesting soy protein). I avoid prescribing soy isoflavone extracts in supplement form unless there is a diagnosed estrogen deficiency that is contributing to menopausal symptoms such as hot flashes, night sweats and vaginal dryness. In this case, I may prescribe a formula that contains soy isoflavones and other phytoestrogen extracts – if appropriate. Before making any recommendations, I assess each woman based on their current breast health, hormone balance and individual risk factors for breast cancer. What might be right for you, may not be for another.

What about men and soy? The phytoestrogens in soy exert a cancer-protective effect in the prevention and treatment of prostate cancer. Dietary soy is associated with a lower risk of prostate cancer. Therefore, moderate dietary consumption of soy (as described above) also applies to men.

The bottom line is that the amount and the type of soy you should consume is dependant on your personal health history as well as your family health history. For most males and females regular, minimal-to-moderate consumption of soy during adolescence and early adulthood will have many health benefits, including reducing the risk of breast and prostate cancer. If you are unsure, consult with a qualified health care practitioner who can help guide you in the right direction. 

Dr. Gurm specializes in integrative oncology (cancer care) and the treatment of hormone disorders. To learn more about cancer care, visit our Integrative Cancer Therapies page. 

As appeared in The Coquitlam NOW

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