Soy and Cancer – Plus: The Soy And Breast Cancer Connection


Soybeans are widely eaten in the Asian diet, but significantly less widely consumed in the West.  Native to China, soybeans are grown around the world.  In the United States they have traditionally been used mostly in livestock feed.  They are recognized, however, as being a good source of protein with little fat and no cholesterol, and an alternative for those who prefer to have less meat in their diet.  There is little argument that soybeans and soy products are a beneficial food choice for people in good health.

Is Soy and Breast Cancer Just The Beginning?

What is the soy cancer connection, however, and is soy and breast cancer related, after all?  Here the answer is a bit murky and has changed a couple times in the recent past.  In the 1990s, soy products were promoted with great enthusiasm as an alternative to meat and all the negative impact animal fats and protein were thought to have.  Population studies showed a clear difference in the incidence of breast and prostate cancers between Asian populations and Western populations.  Although there were a number of lifestyle factors which had to be considered in determining the cause of these differences, one factor which received a good deal of attention was the amount of soy consumed, with Asians eating far more soy than Westerners.  Soy was being recommended for women at risk of developing breast cancer, or for survivors to prevent a recurrence.

As more research was done, however, medical opinion started to shift.  Studies discovered that soybeans are high in phytoestrogens, estrogen-like compounds found in plants.  Studies were conducted in an attempt to determine the effects of these phytoestrogens, notably isoflavones, flavonoids, lignans and coumestans, within the human body, particularly their impact on the development of breast cancer.

Some studies indicated that the phytoestrogens may create an internal environment which encourages tumor growth.  Others, however, indicated that the phytoestrogens may link with estrogen receptors and deliver a weaker estrogen signal than natural estrogen, inhibiting the growth of cancer cells.  This was particularly true of estrogen-dependent cell growth, such as estrogen receptor positive breast cancer.

Soy And Cancer – What The Statistics Say

The indeterminate nature of the research led many scientists to recommend against soy products for patients at risk until there was a clearer understanding of soy’s function in the body.  Recent studies, however, have shifted the focus yet again.  One study compiled data on 18,000 women who were diagnosed with invasive breast cancer.  Nine years after diagnosis, researchers found no significant statistical difference between the women who ate a large amount of soy versus those who ate little or none.

Another research team studied the effects of commercial soy products administered to a small group of men with prostate cancer and a rising prostate-specific antigen (PSA) level.  Out of 10 test subjects, 5 of them demonstrated a link between long lasting beneficial effects and soy supplementation.

Finally, a recent editorial in the Journal of the American Medical Association assured clinicians that soy products are safe for their patient’s with breast cancer and may even offer some long term health benefits.

As a mention-worthy aside, a study conducted in China but the School of Public Health from Perth, Australia concluded that soy and isoflavone consumption correlates with a reduced risk of ovarian cancer.

So, Does Soy Cause Cancer or Is It Healthy?

Soy, then, isn’t the wonder food once hoped for, nor is it the clear cut bad villain.  It’s a nutritious source of protein that may have some other long term benefits as well.  It is important to understand, however, that all the recent studies have used natural soy foods, consumed in moderate amounts.  The best way to take soy is as part of a balanced meal.  Unnaturally high portions of soy available as supplements were not used in the tests, nor are they included in the researchers’ recommendations.






South Med J. 2011 Nov;104(11):736-40.

Effects of Commercially Available Soy Products on PSA in Androgen-Deprivation-Naïve and Castration-Resistant Prostate Cancer.

Joshi M, Agostino NM, Gingrich R, Drabick JJ.



From the Division of Hematology/Oncology, Penn State Hershey Cancer Institute,Penn State Milton S. Hershey Medical Center, Hershey, PA.

Soy and isoflavone intake are associated with reduced risk of ovarian cancer in southeast china. Zhang M, Xie X, Lee AH, Binns CW. 2004