People who ate soy regularly as children have a lower risk of breast cancer, researchers reported on Tuesday.
And men who eat fish several times a week have a lower risk of colon cancer, a second team of researchers told a meeting in Boston of the American Association for Cancer Research.
The studies add to a growing body of evidence about the role of diet in cancer. Cancer experts now believe that up to two-thirds of all cancers come from lifestyle factors such as smoking, diet and lack of exercise.
Dr. Larissa Korde of the National Cancer Institute and colleagues at the University of Hawaii studied studied 597 Asian-American women with breast cancer and 966 women without the disease. The mothers of some of the women were also available to answer questions about what they fed their daughters as children.
The 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, the researchers found.
"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.
It is not clear how soy might prevent cancer, although compounds in soy called isoflavones have estrogen-like effects.
A second study presented at the same meeting showed that men who ate fish five times a week or more had a 40 percent lower risk of developing colorectal cancer compared to men who ate fish less than once a week.
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.
"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," said Megan Phillips, a doctoral student at the Harvard School of Public Health, who led the study.
Many kinds of fish are rich in omega-3 fatty acids, which in turn interfere with the cyclooxygenase-2 or COX-2 enzyme.
COX-2 affects inflammation, which may play a role in tumor growth.
Men who ate the most fish had a 40 percent lower risk of developing colorectal cancer over the next 19 years, the researchers found. Eating fish twice a week lowered the risk by 13 percent. Aspirin did not add any extra benefit or risk.
A separate study published on Monday found that eating red meat raised the risk of breast cancer in women.
