Vanderbilt-Ingram Cancer researchers have found that a lower risk of breast cancer recurrence comes with eating more soy. That study is out in the latest Journal of American Medicine.
The study looked at data from over 5 thousand women who survived breast cancer in China in the last eight years. It found the more soy a woman ate, the lower her chance of cancer recurrence.
Vanderbilt researcher Xiao-Ou Shu says that may be because soy contains isoflavones, which are similar to estrogen – a major cause of breast cancer. Because isoflavones can compete with estrogen for receptors, Shu says they may help reduce the effects of estrogen.
The study tracked women for an average of four years, so Shu says researchers’ next move will be following up over a longer timeline.
Tamoxifen is a drug designed to interrupt estrogen. Shu says there had been some question in lab research as to whether soy would help or hinder tamoxifen, but the new study indicates women consuming soy – up to 11 grams daily – had lower rates of recurrence, whether they used tamoxifen or not.
Shu also cautioned isoflavones aren’t the only benefit of consuming soy, which provides folate, calcium, fiber and vitamins. So she says it would be premature to infer isoflavones alone – in the form of soy capsules – would yield the same benefits.
And Shu noted other beneficial behaviors were associated with eating soy in the study, but even so she says the correlation between soy and survival remains strong.
“We do find that survivors that ate a lot of soy food are likely to also have other healthy lifestyles: they eat more vegetables, they exercise a little more, eat a little more fish. But we have adjusted those factors in our statistical analysis and we see that the soy and breast-cancer outcome association is quite robust.”
Shu says a similar study was published earlier this year with a smaller group. Those earlier results were encouraging, Shu says, but not conclusive – only “suggestive.”
“Our study has a larger sample size and a better methodology, so our study is much more conclusive.”
Grants from the U.S. Department of Defense Breast Cancer research program and the National Cancer Institute supported the study.