There has been conflicting evidence as to whether soy foods increase breast cancer risks or reduce the chances of breast cancer.

With soy products of all kinds gaining in popularity, women are concerned about consumption when they are at risk of or have experienced breast cancer.

Now, there is new evidence indicating soy foods may actually benefit women that eat moderate amounts by reducing their risk of breast cancer recurrence and lower their risk of death.

Because soy contains isoflavone, an estrogen-like compound which in labs seemed to help cancer cells to grow and increase tumor growth in animals, many breast cancer patients have worried that by eating soy products they may be increasing their odds of recurrence or death.

However, based on a new study published in the December 9^th issue of the Journal of the American Medical Association, there seems to be no reason for breast cancer patients to avoid soy foods.

The lead author of the newly released study, Dr. Xiao Ou Shu, a professor of medicine at Vanderbilt University, and her colleagues used data from the Shanghai Breast Cancer Survival Study that consisted of 5,042 Chinese women ranging in age from 20 to 75 that had been diagnosed with breast cancer between March 2002 and April 2006, for their study.

The group examined data on cancer progression at six months following a breast cancer diagnosis, and again at 18, 36, and 60 months following the diagnosis. The group considered the cancer diagnosis, treatment, and lifestyle factors of the patients, including their diets.

Dr. Shu said, “There was a linear response, and we found the higher the intake, the lower the mortality, up to 11 grams of soy protein.” 

One-fourth of a cup of tofu daily would grant someone 11grams of soy protein, according to Dr. Shu. The study found the group of women with the highest intake of soy products had a 29 percent lower risk of death, and a 32 percent less chance of suffering a recurrence of breast cancer, when compared to the group of ladies that consumed less than 5.3 grams of soy daily during the study. 

Dr. Shu said, “Some doctors have advised women not to eat soy foods…. But another school of physicians think it’s safe. So it has been controversial.

Our findings are important because, nowadays, it’s very difficult to avoid soy exposure. Soy flour and soy protein has been added to many foods in this country. Women may consume it and not even know it.”

Dr. Shu and her colleagues didn’t notice any adverse effects caused from soy consumption in women with estrogen receptor-positive breast cancer, a form of cancer where tumors grow faster when exposed to estrogen or in those cancer patients with estrogen receptor-negative, a type of breast cancer thought to not be affected by estrogen.

The study also found no difference in women who were taking Tamoxifen, a drug used to treat breast cancer patients, or breast cancer patients not taking the drug. 

However, it seems based on Dr. Shu’s study patients taking Tamoxifen and consuming lower to moderate amounts of soy products benefited from a lower risk of death.

But women who consumed the most soy products and were not taking Tamoxifen, had the highest rates of survival and lowest chances of recurrence, compared to those taking the drug and eating less soy. 

While the new research brings more insight into the link between soy products and breast cancer survival and recurrence rates, there is still a lot of research needed.

This study was based on soy consumption in Chinese women which differs from the consumption in women in the U.S. While this study gives us a little reassurance as far as soy products being safe if consumed by a breast cancer patient, the author states, “we cannot conclude from this study that there are no negative effects” of soy.

Dr. Shu cautions that her study was considering soy as a whole food and not its components and there could be some components of soy that are not good for everyone.

However, she said overall they are seeing women who eat more amounts of soy are helping in their fight against breast cancer recurrence and death.