Regular screening for colon cancer, including a colonoscopy, provides the best preventative medicine

BOSTON (CNN) -- In a surprising finding that contradicts conventional dietary wisdom, Harvard University researchers have discovered that a high-fiber diet does not appear to reduce the risk of colon cancer.

However, the researchers and other cancer specialists stress that a diet high in fiber -- which comes from fruits, vegetables and whole grains -- has other health benefits that still make it worthwhile.

"It's still a very good idea to eat a diet that's high in fresh fruits and vegetables, both for its direct benefit on heart disease and reducing adult-onset diabetes," said Dr. Michael Thun of the American Cancer Society.

"People should base their behavior on all of the evidence, rather than on one study," he said.

In the study, published in the latest New England Journal of Medicine, researchers tracked the colon and rectal health of more than 88,000 women who participated in the Harvard-based Nurses Health Study from 1980 to 1996.

Of the women studied, 787 developed colon or rectal cancer. The risk was the same, regardless of how much fiber they ate.

Previous studies in men also found that fiber does not lower the risk of colon cancer, and the researchers said they also believe their findings would apply to men.

The researchers said they were astounded by the findings, which contradict the conventional thinking about the link between fiber and colon cancer.

"As a practicing physician and as a researcher, this is a hypothesis that has stood the test of time," said Dr. Charles Fuchs of the Dana-Farber Cancer Institute. "There has been such an abundant enthusiasm for this hypothesis, so the important message here is that fiber, overall, has no protective effect."

The recommended amount of fiber for a healthy diet is about 30 grams per day, about five to eight servings of fruits and vegetables. Thun said he doubts his organization will change its nutritional guidelines because people who eat more fiber generally suffer fewer cases of cancer of the mouth, throat, larynx, esophagus, stomach and lungs.

He also stressed that there may be other properties of vegetables, including the vitamin folate, that could lower the risk of cancer and that people who eat more fruits, vegetables and whole grains also tend to be less obese and suffer fewer health problems.

To protect against colon cancer, regular screening by a doctor is the best prevention. That may include a colonoscopy to look for polyps and cancer.

Patients whose colon cancer is found early, before any symptoms are present, have a 90 percent chance of surviving the disease.

Medical Correspondent Dr. Steve Salvatore contributed to this report.