Northwestern study finds soy negatively impacts breast cancer patients

Daniel Schlessinger

Just in time for Breast Cancer Awareness Month, a new Northwestern study finds dietary supplements traditionally used to treat breast cancer patients may do more harm than good.

Although concentrated soy was once marketed as beneficial for women with breast cancer, the study shows soy supplements have a negative effect on some women with breast cancer. The research was published Feb. 2 in the journal Cancer Prevention Research.

Soy’s effects on cancer are based off a component called genistein. Dr. Raymond Bergan, a Feinberg professor and one of the study’s authors, had previously found genistein had a positive effect on men with prostate cancer. Other studies at the cellular level had indicated genistein had a positive effect on breast cancer. However, Bergan said these findings do not apply when looking at the whole body on a macroscopic level, which he views as more accurate.

“Genistein has some anti-cancer properties,” Bergan said. “But we definitely found it doesn’t have a positive effect on breast cancer, and we found some potential negative effects that were concerning, especially in premenopausal women.”

Bergan said he and and lead study author Dr. Seema Khan had seen the previous studies but wanted to test humans to confirm the effects. Their tests followed 98 women with breast cancer over six months as some took soy supplements and the others took a placebo.

Bergan said the discrepancy in the previous data and their data revolves around hormones. When genistein was undergoing microscopic testing, it wasn’t surrounded by other hormones in the body.

When tested in humans, scientists were able to observe genistein’s effects around large amounts of estrogen.

“Estrogen is necessary for the growth and formation of the breasts,” Bergan said. “But it also is a stimulator of cell growth that will stimulate the cancer growth.”

Bergan was quick to note this does not mean soy is harmful in food, even for women with breast cancer. Tofu or other soy products contain genistein in such small amounts that it would likely have no effect on cancer cell growth at all, he said.

Supplements differ from normal foods, though, because they contain the essential components of foods in concentrated amounts. Soy supplements may contain much more genistein than normal soy products do, so eating supplements regularly may have a negative effect, he said.

“An apple a day is good for you,” Bergan said. “Now, if I were able to put 1,000 apples into a pill and say take one a day, it might not be so beneficial.”

The U.S. Food and Drug Administration has struggled in the past with supplement producers, Bergan said, because it is difficult to qualify uses as indications. Bergan said supplement makers do not undergo rigorous FDA testing for their products because they “will rarely say any specific medical use that would require FDA scrutiny.”

If a woman has breast cancer or is at high risk for it, Bergan said normal soy products are acceptable but supplements that contain soy in concentrated amounts should not be consumed.

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