Study: Adolescents Who Eat Soy Reduce Risk of Breast Cancer

Adolescents who eat soy foods on a regular basis may be lowering their risk of developing breast cancer, according to researchers at the University of Southern California.

Asian-American women who ate soy foods weekly during adolescence and adulthood had about half the risk of developing breast cancer as Asian-American women who ate little soy, according to the report in the journal Carcinogenesis.

The risk was also lowered for women who ate soy regularly during adolescence but ate little soy in adulthood. However, there seems to be little added benefit for women who ate little soy during the teen years but high amounts of soy as adults.

"There has been a lot of talk and controversy about the Asian diet and connections between soy food intake and breast cancer, said Anna H. Wu, PhD, professor of preventive medicine at USC. "We wanted to look at soy very carefully, to better understand if soy by itself is protective or if the level of soy consumption is just a marker for acculturation."

Researchers conducted a study of Chinese, Japanese and Filipino women in Los Angeles County to assess the importance of soy in lowering the risk of breast cancer. From 1995 to 1998, 501 Asian-American breast cancer patients were interviewed and compared to 594 healthy Asian-American women.

Study participants were asked about their eating habits, including how many times each week they ate tofu as a teenager. They were also asked about the frequency and amounts of whole soy foods, such as tofu, soymilk, miso and fresh soybeans, they ate as adults.

Chinese women had the highest intake of soy (26.8 milligrams of isoflavones per day), followed by Japanese women (18.4 mg) and Filipano women (9.3 mg). Migrant women ate a little more soy than women born in America. More than 90 percent of the Chinese and Filipino women in the study were born in Asia, compared to less than 30 percent of the Japanese women.

Researchers grouped the women by how often they ate soy during adolescence and adulthood and found that women who consumed a high amount of soy during both periods had a 47 percent reduction in risk of developing breast cancer. Women who ate little soy during adulthood but were regular soy eaters during adolescence had a 23 percent reduction in risk.

Women who ate little soy during adolescence but ate a lot of soy as adults showed little reduction in risk. Because the number of women with this soy eating pattern was so small, researchers caution that this particular result needs to be confirmed by larger studies.

A much larger study is also needed to sort out the benefits of adult soy food intake and what levels of soy intake are most helpful, added Wu.

Other sources: University of Southern California