High-Fiber Diet Helps Prevent Colon Cancer

FRIDAY, May 2, 2003 (HealthDayNews) -- In the latest evidence pointing to the benefits of eating fiber, researchers on both sides of the Atlantic report a high-fiber diet sharply reduces the risk of colon cancer.

That conclusion, in two studies in the May 3 issue of The Lancet, reinforces earlier medical advice recommending high-fiber diets.

Other studies in recent years, however, have found high-fiber diets provided no protection against colon cancer, calling into question long-held beliefs.

In the European study, which the researchers called the largest ever on the relationship between diet and cancer, the scientists tracked more than a half million people in 10 countries for an average of 4 1/2 years.

Those who averaged 35 grams of daily fiber intake had a 25 percent lower risk of colorectal cancer, primarily colon cancer, compared with those who averaged 15 grams of fiber a day, the study found. The correlation proved strongest for colon cancer and was not statistically relevant for rectal cancer, the study says.

A close examination of more detailed dietary data for about 32,000 people in the European study yielded even more promising results. It showed that those who consumed 35 grams of fiber daily had a 40 percent lower risk of cancer than those who ate 15 grams daily, according to the study.

"The most interesting thing is, it does actually confirm all the other studies prior to the most recent ones," which found no relationship between high-fiber diets and cancer, says Sheila A. Bingham, the lead author of the European study.

"Eat more plant foods because then you're eating more whole-grain cereal, more fruits and vegetables -- that's the message coming through," adds Bingham, head of the diet and cancer group at the UK Medical Research Council's Dunn Human Nutrition Unit in Cambridge.

The U.S. study focused on 37,600 people, about 3,600 of whom had non-malignant polyps -- precursors to colon cancer. Based on surveys, researchers divided the people into five groups, according to their fiber consumption.

Those who ate the most fiber, an average of 36.4 grams a day, had a 27 percent lower risk of the polyps than those who ate the least fiber, averaging 12.6 grams a day, the study found.

To achieve those protective effects, the latest research suggests, Americans would have to consume much more fiber than they currently do. The U.S. study says Americans average about 16 grams of fiber a day.

"You really can see the risk [of colon cancer] is going down when the fiber is increasing; it's a very strong trend," says Ulrike Peters, the lead author of the U.S. study. "This is a positive finding because it is consistent with health recommendations" for fiber intake, adds Peters, a researcher at the National Cancer Institute.

Both studies looked at fiber in foods only, drawing no conclusions about the potential protective value of fiber in dietary supplements.

Bingham says it's "very strange" that some earlier studies did not show the same protective effects of fiber. She suggests earlier research could have mistakenly concluded fiber had no preventive effect because of smaller amounts of fiber eaten and less variety in the amounts and types.

But Dr. M. Robert Cooper, the principal investigator of the 2000 Polyp Prevention Trial, says he stands by its findings that a high-fiber diet doesn't protect against colon cancer.

For four years, the Polyp Prevention Trial followed almost 2,000 patients believed to be at high risk for colon cancer because they had had pre-cancerous polyps removed.

Half of them were told to follow a diet that included five to eight servings of fruits and vegetables and at least 18 grams of dietary fiber for every 1,000 calories a day, with no more than 20 percent of their calories from fat. The other half of the study participants got dietary counseling but did not change their eating habits much.

The rate of recurrence of polyps was the same for both groups in the "rigidly controlled" trial, says Cooper, a professor emeritus of hematology and oncology at Wake Forest University Baptist Medical Center.

"It's not a major factor in preventing colon cancer," Cooper says of fiber. "We need to go on to something that's more significant than fiber," he adds, calling for more emphasis on screening for colon cancer.

More information

For tips on getting enough fiber in your diet, visit the American Cancer Society. To learn more about colorectal cancer, check with the National Library of Medicine.