Women who eat more high-fiber foods during adolescence and young adulthood—especially lots of fruits and vegetables—may have significantly lower breast cancer risk than those who eat less dietary fiber when young, according to a new large-scale study led by researchers at Harvard T.H. Chan School of Public Health.

The study was published online February 1, 2016 in Pediatrics.

“Previous studies of fiber intake and breast cancer have almost all been nonsignificant, and none of them examined diet during adolescence or early adulthood, a period when breast cancer risk factors appear to be particularly important,” said Maryam Farvid, visiting scientist at Harvard Chan School and lead author of the study. “This work on the role of nutrition in early life and breast cancer incidence suggests one of the very few potentially modifiable risk factors for premenopausal breast cancer.”

The researchers looked at a group of 90,534 women who participated in the Nurses’ Health Study II, a large long-running investigation of factors that influence women’s health. In 1991, the women—ages 27-44 at the time—filled out questionnaires about their food intake, and did so every four years after that. They also completed a questionnaire in 1998 about their diet during high school. The researchers analyzed the women’s fiber intake while adjusting for a number of other factors, such as race, family history of breast cancer, body mass index, weight change over time, menstruation history, alcohol use, and other dietary factors.

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