Any woman who's been diagnosed with breast cancer asks her doctor what she can do to avoid a recurrence. Sometimes the answer is nothing, since aggressive cancers can quickly spread throughout the body regardless of what a woman does. She can, though, lower her chances of having a relapse by taking steps to reduce levels of estrogen, thought to trigger the growth of the most common breast tumors. This can be achieved by minimizing alcohol, adding exercise, and shedding excess body fat. But one recommendation—to avoid soy foods—can probably be stricken from this list, according to a new study published in the Journal of the American Medical Association.
High in plant estrogens, soy-rich foods like soybeans, tofu, soy milk, and tempeh have been considered by some experts to be no-no's for breast cancer patients because they were thought to proliferate the growth of tumor cells and possibly to negate the effects of antiestrogen drugs like tamoxifen. But the new research, which involved more than 5,000 Chinese breast cancer survivors, found that those who had the highest intake of soy foods (more than 15 grams of soy protein a day) had about a 30 percent lower death rate and nearly a 30 percent lower rate of recurrence than those who ate the least amount of soy (5 grams or less per day). That's probably because soy also contains compounds that have anticancer effects. The researchers controlled for confounding factors like body mass index, exercise habits, tumor stage, and other differences in diet.
The study didn't find any extra benefits from taking more than 15 grams of soy protein a day, which means breast cancer patients shouldn't start popping soy protein supplements. That said, they also shouldn't worry about eating soy. "Patients with breast cancer can be assured that enjoying a soy latte or indulging in pad Thai with tofu causes no harm," National Cancer Institute researchers Rachel Ballard-Barbash and Marian Neuhouser write in an editorial that accompanied the study, "and, when consumed in plentiful amounts, may reduce risk of disease recurrence."