Challenging conventional wisdom, a new study finds eating high-fiber foods does not cut your risk of colon cancer – but don’t banish the broccoli, experts say.
The study, published today in the New England Journal of Medicine, tracked 88,757 nurses from 1980 to 1996.
During that time, 787 of the women taking part in the Harvard-based Nurses Health Study developed cancer of the colon or rectum.
Researchers said they were surprised to find women on low-fiber diets were no more likely to develop colon cancer than those who stuck to fiber-rich foods like bran, fruits and vegetables, dried fruits, beans and whole grains.
“We found no evidence that dietary fiber reduces the risk of colorectal cancer,” they said. The theory that a high-fiber diet can guard against colorectal cancer goes back about 25 years.
“There has been such an abundant enthusiasm for this hypothesis, so the important message here is that fiber, overall, has no protective effect,” said the study’s lead researcher, Dr. Charles Fuchs of Brigham and Women’s Hospital in Boston.
But Fuchs pointed out fiber helps protect against other conditions like high blood pressure and heart disease – and people eating it for those reasons should “keep doing it.”
“If the primary concern is to prevent colon cancer, then I wouldn’t try fiber. I’m not sure that’s going to work,” he said.
But Dr. Naomi Nakao, a Manhattan gastroenterologist, said she will not stop urging her patients to stay on fiber-rich diets to guard against colon cancer, based solely on one study.
“I would like to see more studies of people at high risk – those who have adenomatous colonic polyps, or have had colon cancer before or have first-degree relatives with colon cancer,” she said.
“I would like to see how a high-fiber diet influences these people,” said Nakao, an associate professor of gastroenterology at Albert Einstein College of Medicine and Beth Israel Medical Center.
Dr. Keith Ayoob, a nutritionist at Albert Einstein and spokesman for the American Dietetic Association, said “even if we don’t consider the colon-cancer issue, the benefits of fiber are well-known for other diseases.”
High-fiber foods help lower the risk of developing various digestive cancers, and have been shown to normalize blood glucose levels in diabetics and to lower the risk of stroke, he said.
“Therefore, the recommendation to eat a high-fiber diet still stands,” Ayoob said. “You’re not just getting fiber, you’re getting a whole host of nutrients and phyto-chemicals.”
Americans should eat a well-balanced diet that includes at least 25 grams of fiber a day – “that’s about double what the average American eats,” Ayoob said.