New Study Finds High Fiber Intake by Young Women May Decrease Breast Cancer Risk

In a study published this week in the journal Pediatrics, BCRF investigator Walter Willett and colleagues at Harvard T.H. Chan School of Public Health in Boston, MA reported that high fiber intake early in life may lower the risk of future breast cancer.

The results of the study showed that those women with the highest intake of total fiber (20 grams or more a day) during adolescence and early adulthood had a 24 percent decreased risk of pre-menopausal breast cancer. Each 10 gram/day increase in fiber intake (equivalent to one apple or two slices of whole wheat bread) during early adulthood was associated with a 13 percent decrease in breast cancer overall.

These findings are important because they add new information about the impact of a diet high in fiber on cancer risk. Previous studies have not shown a significant influence of fiber on breast cancer risk, but this is the first study to look at fiber intake during adolescence and early adulthood, an important time in breast development when environmental exposures can have long-term effects. The conclusions of this study are supported by findings in an earlier study by BCRF investigator, Graham Colditz in which a high fiber diet during adolescence was associated with a decreased risk of benign breast disease, a marker of increased risk of breast cancer.

Diets high in fiber typically include fresh vegetables and whole grains, which are also rich in phytochemicals and healthy fats that could contribute to the protective effect. Although the current study cannot rule out the influence of other protective factors in the high fiber diets, it supports the notion that diet and lifestyle factors early in life impact future breast cancer risk.

The researchers used diet records collected from 90,534 women in the Nurses Health Study II (NHSII), an ongoing prospective study involving more than 116,000 women looking at a variety of factors influencing women’s health. In the current study, the researchers assessed fiber intake during the teen-age years and early adulthood and tracked the number of new cases of invasive breast cancer over a 20-year follow up period.

To avoid confusing the effect of fiber with other possible influences on risks, the researchers removed other factors, including race, family history, smoking, body mass index at age 18, adult weight changes (after 18 years old), alcohol consumption, exercise and contraception use from the analysis. Because high fiber diets tend to be healthier diets overall, their analysis accounted for the influence of a healthy diet, including low red meat and animal fat consumption. 

BCRF has supported the work of both Dr. Willett and Dr. Colditz since 2001 and 2004, respectively. Both researchers are leaders in the field of cancer prevention and epidemiology, with a strong focus in diet and lifestyle factors on breast cancer risk and survival. Their work is part of BCRF’s larger research grants portfolio in cancer prevention, which totaled more than $6 million in 2015 alone.