Fiber and cancer risk

Belief debunked: Popular diet may be healthful, but doesn't prevent colon cancer.

April 28, 2000

IT MADE all the scientific sense in the world and it was an easy fix. But a high-fiber, low-fat diet is no prevention against deadly colon cancer, major medical studies show.

The highly touted regimen, promoted by doctors for decades, now equates to another alternative medicine treatment. At least in the results of a four-year U.S. study of men and women who were at high risk for colon cancer, the second leading cause of cancer death. And in a three-year study of at-risk persons who ate extra bran fiber.

It shows how much we do not really know about the complex disease of cancer and how many unknown factors -- from genes to environment to diet -- can play a role in its development. The disappointing clinical results demonstrate that there is no simple prevention for cancer of the colon.

For years, scientists felt there was a compelling foundation of evidence that a fiber diet reduced cancer risk, warranting its use by many millions of believers.

It began with observational studies in Africa and laboratory animal tests that supported the hypothesis. Researchers theorized that because fiber produced a bulkier stool that moved faster through the intestines, it could reduce (and dilute) the impact of cancer-causing substances in food on the colon. Less fat consumed results in fewer cell-damaging bile acids secreted by the liver, they knew, so there was probably reduced damage to the intestine.

Some previous studies did not produce evidence that the fiber diet reduced the risk of colon cancer. But they were not as rigidly controlled as the $25 million study by the National Cancer Institute whose surprising findings were reported this month. Those scientists caution that a regimented high-fiber diet may be effective if begun earlier in life or followed over a longer time period.

Still, physicians advise that a diet of low fat, high fiber and ample fruit and vegetables can be helpful for heart disease, weight control and diabetes. It may also be useful in preventing other types of cancer. But bran is clearly no magic potion against colon cancer.

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