Benefit of Soy?
Now, this is a really interesting study from Shanghai (the Shanghai Breast Cancer Survival Study). Among other things, the researchers looked at the use of dietary soy by women who had been diagnosed with breast cancer. The surprise finding was that, especially for women who had taken tamoxifen, there was a survival benefit. Obviously, women who had taken tam had estrogen reception (ER) positive breast cancers. Since soy is known to be a phytoestrogen, we are normally advised to try to avoid it--at least in amounts beyond occasional tofu. It makes sense to me that this avoidance might be a larger problem for many women in China where tofu is a more standard part of the diet. That, however, would not influence a well-done piece of research.
Since the findings of this one study completely contradict the conventional wisdom, it obviously becomes an "ask your doctor" situation. If, however, soy is important to you, it seems worth asking. Here is an excerpt and then a link to read more:
Results of this large, population-based study showed that higher soy food intake was associated with decreased mortality and recurrence after diagnosis of breast cancer. Thus, moderate soy intake is safe for women diagnosed with breast cancer, including those taking tamoxifen, and may even provide a benefit.
STUDY IN CONTEXT
Evidence suggests that the consumption of soy food is inversely related to the risk of breast cancer. A concern exists that, because soy isoflavones compete with endogenous estrogens for estrogen-receptor (ER) binding, soy foods may induce estrogenic effects,
thus increasing the risk of breast cancer recurrence and negatively affecting survival. In addition, laboratory studies suggest that soy isoflavones may interact with tamoxifen. The Life After Cancer Epidemiology study, which evaluated the effect of soy isoflavone intake and recurrence, showed that soy consumption may reduce the risk of breast cancer recurrence in women who have been
treated with tamoxifen. In this article, Shu et al report the results of a longitudinal study of the effect of soy consumption on recurrence after a breast cancer diagnosis in 5033 Chinese women. The analysis examined relationships between recurrence and mortality outcomes and ER status and tamoxifen use.