Women who consume more dietary fiber when they are teens and young adults appear to have a reduced risk of contracting breast cancer, according to a recent study by researchers at the Harvard T.H. Chan School of Public Health.
(Formerly the Harvard School of Public Health, the school was renamed in 2015 following a $350 million gift from the Morningside Foundation, established by the late T. H. Chan. The gift was the largest ever received by Harvard.)
The study was published online Feb. 1 in Pediatrics.
“Previous studies of fiber intake and breast cancer have almost all been non-significant, 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.
Breast cancer risk was 12-19% lower among women who ate more dietary fiber in early adulthood, depending on how much more they ate. High intake of fiber during adolescence was also associated with 16% lower risk of overall breast cancer and 24% lower risk of breast cancer before menopause.
Among all the women, there was a strong inverse association between fiber intake and breast cancer incidence. For each additional 10 grams of fiber intake daily—for example, about one apple and two slices of whole wheat bread, or about half a cup each of cooked kidney beans and cooked cauliflower or squash—during early adulthood, breast cancer risk dropped by 13%.
The greatest apparent benefit came from fruit and vegetable fiber.
The authors speculated that eating more fiber-rich foods may lessen breast cancer risk partly by helping to reduce high estrogen levels in the blood, which are strongly linked with breast cancer development.