Soy may lower death risk from breast cancer, but questions remain

Dec 9, 2009 10:21 AM

"Well does soy cause breast cancer, or doesn’t it?" asked a close friend a few weeks ago at dinner in our favorite sushi restaurant. "Well…it’s debatable," I said, and then finished scarfing down the bowl of edamame in front of me. Bad answer and not the answer any woman really wants to hear.

We all know soy is good for you. It’s not only high in protein and fiber, findings suggest it can help lower LDL (bad) cholesterol and fight certain cancers, including cancer of the colon and prostate. But on the topic of soy and breast cancer, questions, like my friend’s, still linger. Soy foods are rich in isoflavones, a group of phytochemicals that have been linked to a reduced risk of breast cancer. However, the estrogen-like effects of the key soy isoflavones and the potential interaction between isoflavones and the breast cancer drug tamoxifen (Nolvadex and generics) have led to concerns about consumption of soy foods in women with breast cancer.

Shining some light on the issue is a study published on Wednesday in the Journal of the American Medical Association that suggests consuming soy foods lowers death and relapse rates in breast cancer patients. The large study looked at 5,042 breast cancer survivors in China between ages 20 to 75 who were diagnosed with the disease between March 2002 and April 2006. Information on diagnosis, treatment, lifestyle exposures after diagnosis, and disease progression were collected on each of the women approximately 6 months after diagnoses and again at 18, 36, and 60 months after diagnosis. Women who consumed the most soy had a 7.4 percent chance of dying within 4 years, compared to 10.3 percent for those who ate the least, and those who ate the most had an 8 percent chance of a recurrence, compared to an 11.2 perent chance for those who ate the least soy.

According to the editorial that accompanied the study, because the study was carried out in China it limits our ability to make inferences to U.S. populations of breast cancer survivors. In China, soy foods represent 10 percent or more of the daily protein intake, and the types of soy foods consumed, such as miso, tofu, and edamame may help provide greater exposure to isoflavones than in the U.S. The soy intake in the U.S., in comparison, is extremely low and is largely based in soy supplements, meats made with soy, and other processed soy foods.

CR’s take: While the findings in this well-designed, large study suggest that consuming soy foods among breast cancer patients is safe, it also highlights the need for further research in this area. Until then, our previous recommendation stands: it's probably safe for most women to consume soy products as long as they don't go overboard. Aim for no more than about 100 mg of isoflavones a day (roughly 15 ounces of tofu, 2 1/2 to 4 cups of cooked edamame, and 3 cups of soy milk). But women who already have breast cancer or are at high risk for it might want to limit their consumption.

—Ginger Skinner

Read more on soy foods in our January issue of Consumer Reports On Health, and take a look at the lifestyle changes that can reduce your breast cancer risk. For more on the isoflavone content in your soy foods, take a look at the USDA's database.

Photo courtesy of yomi955