"[This] study further highlights the importance of eating a healthy diet for reducing the risk of cancer," said Ed Yong, information officer for Cancer Research UK.
Researchers found no significant effect, however, on the breast cancer risk of post-menopausal women. Janet Cade, who headed the study, says that this is why no one has noticed the effects of fiber on breast cancer before.
"Previous research hasn't shown a convincing link between increased dietary fiber and the lower risk of breast cancer," Cade said. "But earlier studies didn't draw any distinction between pre- and post-menopausal women."
According to the study's authors, there are three possible reasons for the anti-cancer effects of a high fiber diet: First, fiber has a stabilizing effect on the body's insulin levels. High insulin levels have been shown to contribute to the risk of cancer. Second, high-fiber foods also tend to be rich in other essential nutrients, including those with antioxidant properties.
Third, and perhaps most relevant, dietary fiber reduces the levels of estrogen in the body, which has been shown to correlate with the risk of breast cancer. These levels are higher in younger women, which may explain the age split that researchers discovered.
According to the study, pre-menopausal women should eat at least 30 grams of fiber per day to reduce their cancer risk. By contrast, the American Dietetic Association recommends a minimum of 25 grams per day for a 2,000-calorie diet.
Breast cancer is the second most fatal cancer among women, after lung cancer. Between one in 13 and one in nine women will contract it at some point in their lives.
The study was funded by the World Cancer Research Fund and published in the International Journal of Epidemiology.
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