Dr. Larissa Korde of the National Cancer Institute and colleagues at the University of Hawaii studied 597 Asian-American women with breast cancer and 966 women without the disease.
They found that women who ate the most soy-based foods such as tofu and miso when aged 5 to 11 reduced their risk of developing breast cancer by 58 percent.
"Childhood soy intake was significantly associated with reduced breast cancer risk in our study, suggesting that the timing of soy intake may be especially critical," Korde said.
A second study presented at the same meeting further consolidated the evidence about the role of diet in cancer.
Megan Phillips of the Harvard School of Public Health and colleagues analyzed data from 22,071 men volunteering for a large, ongoing study of physicians. They found that men who ate fish at least five times a week had a 40 percent lower risk of developing colorectal cancer compared to peers who ate fish less than once a week.
"We already know that eating fish can reduce the risk of sudden cardiac death, and this might provide another reason to add fish to your diet," Phillips said at the meeting.
Researchers believe the health effects of fish consumption in relation to colorectal cancer may lie in their content of the n-3 fatty acids that can inhibit the cyclooxygenase-2 or COX-2 enzyme.
COX-2 affects inflammation, which may play a role in tumor growth.
The studies promote the belief by several cancer experts that up to two-thirds of all cancers come from lifestyle factors such as smoking, diet and lack of exercise and that diet can play a crucial role in lowering the risk of cancer, or in reducing the aggressiveness of the disease.
