The Pros and Cons of Soy: More Study Needed

Soy milk, tofu and edamame are just a few of the many soy-rich foods touted for helping individuals reduce cholesterol levels and minimize risk of heart disease. But is soy just as beneficial for fighting cancer?

A recent study indicates that it is, but the question of whether tofu and other soy-rich foods can combat tumor growth has yet to be definitively answered.

The effects of soy have been known to produce both positive and negative results in breast cancer patients, particularly because of the chemical makeup of isoflavones in soy. These isoflavones are similar to estrogen in structure. As they bind to estrogen receptors, they can either stimulate or inhibit estrogen-related tissue development, including breast tumors.

Too early to recommend soy-rich diet
A 2010 study indicated that women with estrogen-positive tumors had a 33% lower risk of recurring breast cancer when they ate higher amounts of soy (59 milligrams of isoflavones daily) compared to those who had the least amount (6.5 mg).

But Banu Arun, M.D., professor in MD Anderson's departments of Breast Medical Oncology and Clinical Cancer Prevention, notes that it might be too early to recommend to American breast cancer survivors an increase in soy-rich foods to reduce the risk of breast cancer recurrence.

The reason? This particular study focused on women in China, where soy consumption is high. Their bodies are already used to its beneficial effects. Many Americans, on the other hand, have a minimal daily intake of soy (1 mg to 3 mg).

"The effect of taking soy might be different in the Western patient population where they aren't eating as much soy," Arun says.

Further study of soy and hormones needed
"This patient population was primed with soy and its good effects, so there may be a favorable milieu in their tissue. Furthermore, we also do not know if patients with certain subtypes of breast cancer might benefit from soy, whereas other patients with another breast cancer subtype might not benefit."

Further studies have yet to be conducted on the effects of isoflavones on a low-soy diet. Researchers speculate that there may be a connection between a high intake of soy and its possible enhancement of hormone-based cancer drugs. In the meantime, Arun isn't advising American breast cancer patients to completely avoid soy products, but rather to be moderate in intake.

"I wouldn't say don't eat soy," Arun says. "Moderate consumption should be fine. I just wouldn't convert to a soy-rich diet to reduce breast cancer recurrence since we don't have the data yet for a Western population."