Study shows soy is not only safe for breast cancer survivors, it may also be beneficial
Despite soy's healthy profile, many women who have had breast cancer are reluctant to eat soy foods. And many cancer doctors caution their patients against doing so.
The concern stems from substances in soy called isoflavones, which behave like weak estrogen in the body. Estrogen, a hormone that controls the menstrual cycle, has been shown to increase the risk of breast cancer in women.
Here's how: Estrogen stimulates cells to divide. Cancer arises from DNA mutations in cells -- errors that occasionally happen during cell division. If one of these spontaneous mutations occurs in a gene that controls cell growth and division, it could lead to the development of cancer.
Another worry is the interaction between isoflavones and tamoxifen, a breast cancer drug that blocks estrogen from cells.
But a study published in the December issue of the Journal of the American Medical Association may set those fears aside. The study, by researchers at Vanderbilt University, says soy foods are safe -- and possibly beneficial -- for breast cancer survivors. They looked at 5,042 women in China who were breast cancer survivors and divided them into four groups based on how much soy they ate. Women who ate low amounts of soy consumed an average of about a half-cup of soy milk a day, while the high-soy-consumption group had about three cups a day.
After four years, 10.3 percent of those who consumed the least soy died, compared with 7.4 percent of those who had the most, leading researchers to theorize that soy did not increase breast cancer occurrence and may have had some protective effect.
Breast cancer specialist Dr. Paula Silverman often gets questions from her patients about whether it's safe to eat soy. Her answer: Go ahead and enjoy.
"I don't think there was good data about that, ever," says Silverman, medical director of the Breast Cancer Program at University Hospitals Case Medical Center. "I've always felt that soy was probably safe." Some years ago, Silverman heard a lecture by a physician who made a compelling argument that plant estrogens and human estrogens are not the same. Silverman thinks the weak estrogens in soy may act more like tamoxifen than like human estrogen. "The bottom line is dietary soy is safe for breast cancer survivors," Silverman says.
The National Institutes of Health says it remains unclear what role dietary soy or soy isoflavone might play in cancer risk. While several large population studies have reported that higher soy intake is associated with a decreased risk of developing various types of cancers, including breast, prostate and colon cancer, other research suggests soy does not have this effect.
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