Cancer & Fiber Failure - Brief Article

A high-fiber diet failed to cut the risk of precancerous colon polyps in two major clinical trials.

The Polyp Prevention Trial randomly divided 1,900 people who had already had a polyp removed into two groups. One got a brochure on healthy eating. The other got counseling to eat no more than 20 percent of calories from fat and to get at least 18 grams of fiber and 3 1/2 servings of fruits or vegetables for every 1,000 calories they ate. But after four years, about 40 percent of the people in both groups got at least one new polyp.

The Wheat Bran Fiber Study randomly assigned 1,300 people with a previous polyp to receive a wheat cereal with either 12 grams or two grams of fiber in a serving. Fiber intake--from all foods--averaged 28 grams a day in the high-fiber group and 18 grams in the low-fiber group. After three years, about half of the people in both groups got new polyps.

One possibility: Fiber from wheat bran and other grains may not prevent colon cancer. "In population studies, cereal fiber is not as closely related to colon cancer as fruits and especially vegetables," says Tim Byers of the University of Colorado Health Sciences Center in Denver.

And the trials tracked new polyps, not cancer, he notes. "It takes ten to 15 years and a sequence of mutations before polyps turn into cancer," says Byers. "Fruits and vegetables may protect polyps so they don't mutate into cancer.

"There are plenty of other reasons to eat fruits, vegetables, and whole grains," he adds. Among them: a lower risk of other cancers, constipation, diverticulosis, and possibly heart disease and diabetes.

New Eng. J. Med. 342: 1149, 1156, 1206, 2000.

COPYRIGHT 2000 Center for Science in the Public Interest
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