
But many of these studies were designed to look at other questions, not the relationship between soy and breast cancer, and experts point out that other diet, lifestyle and genetic factors may be at play in the lower cancer rate. In their view, these studies do not provide evidence that eating soy helps prevent cancer.
"When we specifically looked at Asian countries, there was a 10 percent reduction in risk, and it was not significant," Dr. Hilakivi-Clarke said.
Also, the Japanese studies were done on women who had eaten soy since they were babies. Many were exposed while in the womb. Because of this, a popular theory is that early exposure to soy may be what protects women from breast cancer.