Research examining the results of 13 studies that included more than 725,000 people found that a high intake of dietary fiber does not reduce the risk of colon cancer. This is the largest study to date, and unlike previous studies, took into account other risk factors that could affect the outcome.
Other Risk Factors Change Conclusions
A first look at the combined data found a 16% lower incidence of colon cancer in the people who had the highest fiber intake. But when the researchers adjusted the figures to take into account other risk factors-such as multivitamin use, folate intake, red meat consumption and milk and alcohol intake-they found that there was no relationship between dietary fiber intake and colon cancer risk.
Problems With Previous Studies
"In general, most previous studies have been inconsistent," says Yikyung Park, who led the study while at the Harvard School of Public Health and who is now a visiting fellow at the National Cancer Institute.
Dr. John A. Baron, professor of medicine at Dartmouth Medical School, says the real problem in reaching a definitive conclusion is that "fiber" is a vague term. "Fiber is just a word," he says. "It's like saying, 'taking a pill' or 'driving a vehicle.' It's such a broad term that it is not helpful."
Fibers often are characterized by the foods that contain them-cereal fiber, vegetable fiber, fruit fiber, Baron says. But there can be great differences between fibers within those families. Some fibers are soluble, some insoluble-insoluble fiber is believed to have the protective effect-and studies generally do not distinguish between the two, he explains.
"Doing research in this area is difficult, and part of the problem has been people making too-optimistic or too-rapid decisions based on studies that have not been definitive," he adds.
This report is certainly not the last word on the issue, Park says. "This is still a very active area of research. Clearly, more studies are needed."
Fiber Still Has Benefits
There are still good reasons why people should consume dietary fiber, Park says. "There are studies showing that dietary fiber reduces the risk of other diseases, such as heart disease and diabetes, so people should continue to eat dietary fiber," she says.