Soy Products and Breast Cancer Patients – There Might Not be a Threat After All

Soy is a product that many health-conscious people pursue, but medical researchers have been concerned about soy products and women with breast cancer. The reason this concern exists is because of soy’s potential impact on estrogen levels, a hormone that has been proven to support the growth of cancerous cells. A newly conducted study, however, suggests that soy foods are not dangerous to breast cancer patients who have survived the cancer. Such soy-rich foods do not increase patients’ risk of recurrence or death by consuming soy products.

The reason why soy has an effect on estrogen levels is because of compounds called isoflavones that are found in soy foods. These bind onto estrogen receptors, mimic estrogen, and block the effects of actual estrogen in the body. Because of this knowledge, soy products and women with breast cancer have been a fearful combination for some time, according to one of the study researchers, Dr. Xiao-Ou Shu, who is a professor of medicine at Vanderbilt Epidemiology Center, Vanderbilt University Medical Center in Tennessee. In addition, a particular breast cancer treatment called tamoxifen also binds to estrogen receptors, so the combination of soy and breast cancer has been something to be avoided because of this dual concern.

For the study, just over 16,000 women from the United States and China answered questions about their intake of soy products, such as tofu and soy milk. The questionnaires were completed by the women approximately 13 months after the diagnosis of their cancer. The outcome of combining soy and breast cancer was assessed about nine years later, including instances of cancer recurrence and death from eating soy products.

The study compared breast cancer patients who ate the greatest amount of soy isoflavones—over 23 mg a day—with those who ate the least amount, which was about .48 mg a day or less. The average intake of soy in Chinese women was 45.9 mg per day while women from the US averaged only 3.2 mg per day. The researchers found no difference in regards to death rate or cancer recurrence between the two groups, despite the huge difference in soy consumption. The conclusion from this finding is that soy foods are not dangerous to breast cancer patients. However, studies are still being performed to examine the interaction between soy isoflavones and the cancer treatment tamoxifen.

This research project was funded by the American Recovery and Reinvestment Act of 2009. While the findings were beneficial and positive for cancer patients worldwide, is the clear that women with breast cancer should proceed with caution when it comes to choosing soy products over other foods due to the unknown interaction between a popular cancer treatment and estrogen receptor blocking soy isoflavones.