Women who eat a diet high in fiber may have a lower risk of developing breast cancer compared to women who eat low amounts of fiber, suggests a new analysis of the published evidence. This analysis helps to reveal the overall impact of fiber on breast cancer risk, even if the results of individual studies are inconsistent.
It is published in the journal, Cancer.
AICR/WCRF’s latest Expert Report, which analyzed the global research on the topic, concluded that the evidence for fiber reducing breast cancer risk was suggestive but too limited to justify a recommendation. Yet the report found strong evidence that fiber plays an important role in lowering colorectal cancer risk and AICR recommends a healthy diet high in fiber.
Highest to lowest dietary fiber intake
In the current analysis, researchers pooled data from 20 relevant observational studies published through 2019. They found that women who consumed the highest amounts of fiber had an 8 percent lower risk of breast cancer compared to women who consumed the least amounts of fiber.
Because the lifetime risk of breast cancer in American women is approximately 1 in 8, this would lower the risk to approximately 1 in 8.6. It is estimated that over 275,000 American women will be diagnosed with breast cancer in 2020, so even small changes in risk can have a substantial impact at the population level.
Highest dietary fiber intake varied widely, with an average high of about 26 grams per day and the ranges varied between 18-34.5 grams, said lead author Maryam Farvid, PhD, Research Scientist of the Harvard T.H. Chan School of Public Health.
“Our study contributes to the evidence that lifestyle factors, such as modifiable dietary practices, may affect breast cancer risk,” said Farvid, who is also investigating breast cancer survival and beverage intake with support from AICR. This shows an association; it does not show fiber causes reduced breast cancer risk, she notes.
Dietary fiber’s key role in cancer risk
“The impact of diet on breast cancer risk is still a very unresolved topic,” says Dr. Nigel Brockton, Vice President of Research at AICR. The results reported in the current study are similar to those reported in the AICR/WCRF Third Expert Report. The specifics differ because “there are some differences in how the analyses have been conducted and how conclusions were reached,” said Brockton.
Yet there is strong evidence that dietary fiber plays a clear role in cancer prevention. AICR research shows that eating high amounts of fiber decreases the risk of weight gain, overweight and obesity. Having too much body fat is a cause of at least a dozen cancers, including post-menopausal breast cancer. AICR’s report also found that diets high in fiber are directly linked to lowering the risk of one cancer: colorectal.
AICR recommends that adults consume at least 30 grams of dietary fiber each day as part of a healthy eating pattern to lower cancer risk. That differs slightly from the U.S. government’s dietary recommendation, which ranges from 22-28 grams daily for women and 28-34 grams daily for men, depending upon age and daily calories.
Even for the lowest national recommendation, Americans are far from meeting these goals. The average woman consumes only about 15 grams of dietary fiber per day and the average man consumes about 18 grams.
Foods that are especially high in fiber include beans, oat bran and lentils. A banana contains approximately 3 grams of fiber, a slice of whole grain bread contains about 2 grams and a baked potato (with skin) contains about 4 grams.
Experts recommend eating a range of plant foods, including whole grains, fruit, vegetables and beans, to meet your daily fiber intake recommendation. Along with weight management, this eating pattern will give you a variety of the nutrients, minerals and phytochemicals that may play a role in cancer prevention and overall good health.
Find the latest AICR research on lifestyle and lower risk of breast cancer here.