Good Food News for Breast Cancer Survivors

Estrogen plays an important role in breast cancer, and estrogen-blocking medications such as tamoxifen are widely used to help prevent recurrence. This quite reasonably has led to concern about foods containing phytoestrogens - naturally-occurring estrogen receptor modulators that are seen mostly in the form of isoflavones. (Remember that isoflavones are types of flavonoids, like those in red wine.)

Soy foods, in particular, are naturally high in these isoflavones, and there has been some controversy over whether breast cancer survivors should avoid soy foods and whether their estrogen-receptor status, whether positive or negative, should make a difference.

The good news is that a team of researchers from Vanderbilt University Medical Center and the Shanghai Institute of Preventive Medicine specifically designed a study to look at the effects of eating soy on breast cancer survivors (JAMA 2009;302(22):2437-2443).

Over 5,000 female breast cancer survivors between the ages of 20 to 75 were recruited to participate in this study, which began in 2002. About six months after each participant received her diagnosis, she met with a study representative who gathered information regarding the woman's usual diet (including detailed information on her soy intake), her diagnosis, receptor status, treatment, lifestyle and other demographic information. The meetings were then repeated and the information was updated after 18 months, 36 months and 60 months.

The researchers grouped the survivor's intake of soy protein into four levels, from less than 5 grams per day to over 15 grams per day (we in the United State typically eat less than 5 grams of soy protein per day from all sources). They then compared those levels with the women's outcomes, taking into account such variables as age, receptor status, Body Mass Index or meat or fish intake. Those women who ate the most soy protein, when compared with those who ate the least, were 32% less likely to have a recurrence of their cancer. When the scientists looked at the amounts of soy isoflavones the women ate, once again the women who ate the most fared much better than those who ate the least: they were 23% less likely to have a recurrence.

The scientists also looked at whether there were a difference between those women whose cancers were estrogen-receptor positive or negative: those women with ER-positive breast cancer who ate the most soy protein reduced their risk of recurrence by 31%, while those with ER-negative breast cancer reduced their risk by 23%.

Finally they compared the soy intake of those women who were using tamoxifen versus those who were not. Those women who were taking tamoxifen and eating the most soy protein were 35% less likely to have a recurrence. Those women who were not taking tamoxifen and were also eating the most soy protein? About the same: A reduced risk of 34%.

What this means for you

This study is still gathering data and more studies are needed to corroborate these findings, but these results are a clear indication that for breast cancer survivors, eating a moderate amount of soy foods is not only safe but may actually help prevent breast cancer recurrence. Show this article to your oncologist and discuss soy foods with him or her before you make any changes in your diet.

First posted: December 9, 2009