A new study has found that consuming more soy could help lower the risk and prevent early deaths from breast cancer in women. Breast cancer patients who ate the most soy foods were 21% less likely to die over nine-and-a-half years than women who ate the least.
The study also found that soy had no bad effects on women with breast cancer fueled by the hormone estrogen, contrary to some fears.
“Our results suggest, in specific circumstances, there may be a potential benefit to eating more soy foods as part of an overall healthy diet and lifestyle,” said Dr. Fang Fang Zhang, an expert in cancer and nutrition at the Friedman School of Nutrition Science and Policy at Tufts University in Massachusetts in the US, who led the study.
“We recommend that readers keep in mind that soy foods can potentially have an impact, but only as a component of an overall healthy diet.”
Researchers have long noted that women living in Asia who eat a lot of soy have far lower rates of breast cancer than women in the West. And some studies have shown that women in other parts of the world who eat a lot of soy also have lower breast cancer rates.
But some laboratory research also shows that compounds in soy called phytoestrogens might interfere with hormone-based cancer treatments, so some doctors have been wary of recommending soy to breast cancer patients.
Zhang’s team studied 6,235 women with breast cancer taking part in a bigger study. They filled out food diaries and have been watched since 1995. Over 9.4 years, 1,224 of them died of various causes.
Those in the top 25% of soy consumption were 21% less likely to die of any cause than those who ate the least soy, the team reported.
The researchers say their study is more diverse than previous studies because 17% of the volunteers were Hispanic, 12% were black and 11% Asian American.
“Although Asian-American women enrolled in the (study) had a higher mean intake of dietary isoflavone than women from other racial/ethnic groups, these intake levels were substantially lower than those of women living in Asian countries,” the team noted.
“Based on our results, we do not see a detrimental effect of soy intake among women who were treated with endocrine therapy, which has been hypothesized to be a concern,” Zhang said.
“Especially for women with hormone-receptor-negative breast cancer, soy food products may potentially have a beneficial effect and increase survival.”
It’s not entirely understood why soy foods have such strong effects. They’re made from soybeans, which are high in fiber. But they also are rich in compounds called isoflavones, which include daidzein and genistein. Genistein can interfere with cell growth and proliferation and that in turn may slow tumors.
Although Americans do not eat as much soy as people in China and Japan, they may still be eating more than they realize. Soy protein is found in many processed foods and is widely used in cereal, infant formula, granola bars, ice cream, and cheese products.
Breast cancer is the No. 2 cancer killer of US women, after lung cancer. Every year, it’s diagnosed in 200,000 women and a few men, and kills around 40,000.