Whether she gets it from fruits, beans, grains or vegetables, dietary fiber appears to at least slightly lower a woman’s risk for breast cancer, a comprehensive new review finds.

The review covered data from 20 different trials involving millions of women. It found that high levels of total fiber consumption “was associated with an 8% lower risk of breast cancer,” compared to low consumption.

The studies only included prospective trials, where a trial is set up and results tabulated as time goes on. Prospective trials are thought to have more validity than retrospective diet/cancer studies, which only ask women what they ate in the past.

The new study is the first such data review involving prospective studies, said a team led by Maryam Farvid of the Harvard T.H. Chan School of Public Health, in Boston.

Beyond the overall reduction in risk, the review also found the anti-cancer benefit of fiber extended to women of all ages.

“A high intake of total fiber also was found to be significantly associated with a decreased risk in both premenopausal and postmenopausal breast cancers,” Farvid’s group noted.

One breast cancer specialist was encouraged by the findings.

“With the risk for breast cancer being as significant as it is, we are always looking for ways in which we can decrease a woman’s risk for developing this disease,” said Dr. Lauren Cassell, chief of breast surgery at Lenox Hill Hospital in New York City.

As to how fiber works its magic, Cassell said that “it is presumed that consumption of total fiber aids in decreasing circulating insulin and growth factors, as well as decreasing estrogen levels, which are [all] known to aid in the development of breast cancers.”

The Boston team noted that American women typically get close to half (45%) of their dietary fiber from whole grains and cereals, with vegetables being the source of about 23% of fiber, and the rest divided between fruits, nuts, beans and seeds.

But the study found it didn’t really matter where the dietary fiber came from: “The reduction in risk appears to be similar for intake of all sources of fiber,” Farvid’s group said.

High daily fiber intake also appeared to have similar benefits for various subtypes of breast cancer, the study found.

“The current study findings support the American Cancer Society dietary guidelines to consume foods rich in total fiber, including fruits, vegetables, and whole grains,” the researchers reported.

Cassell seconded that notion.

“Even if there is only a modest risk reduction, adding all types of fiber to your diet, particularly fiber that comes from fruit, is easy and has many other added benefits to one’s digestion and diet,” she said.

The study was published online April 6 in the journal Cancer.

More information

For more about breast cancer, visit the American Cancer Society.