Fiber May Not Protect Against Colorectal Cancer
The largest study ever found no reduced risk
TUESDAY, Dec. 13, 2005 (HealthDay News) -- Here's the latest word on whether a diet rich in fiber helps prevent cancer of the colon and rectum: Probably not.
While several studies have found a lower risk of colorectal cancer for people who have a high intake of dietary fiber, a new study that combined the results of 13 studies including more than 725,000 people found no overall protective effect when all risk factors were taken into account.
A first look at the data did find a 16 percent lower incidence of the cancer in the 20 percent of people with the highest fiber intake. But then the researchers began compensating for other risk factors -- such as multivitamin use, folate intake, red meat consumption, milk and alcohol intake.
As a result, "we did not find support for a linear inverse relationship between dietary fiber intake and risk of colorectal cancer," the researchers wrote.
The study results appear in the Dec. 14 issue of the Journal of the American Medical Association.
So, what about those prior studies suggesting fiber had a protective effect?
"In general, most previous studies have been inconsistent," said Yikyung Park, lead author of the journal report. She led the study while at the Harvard School of Public Health and is now a visiting fellow at the National Cancer Institute.
"To date, this is the largest study and we found that dietary intake of fiber did not lower risk," she said.
But this report is certainly not the last word on the issue, Park added. "This is still a very active area of research," she said. "Clearly, more studies are needed."
The real problem in reaching a definite conclusion is that "fiber" is a vague term, explained Dr. John A. Baron, professor of medicine at Dartmouth Medical School, who wrote an accompanying editorial in the journal.
"Fiber is just a word," he said. "It's like saying 'taking a pill' or 'driving in 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 said. But there can be great differences between fibers in those families. Some fibers are soluble, some insoluble -- the insoluble type is believed to have the protective effect -- and studies generally do not distinguish between them, he said.
"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," Baron said.
Asked if he would give dietary advice on the subject, Baron said, "I would pull back from making recommendations from this study or any study regarding colorectal cancer and fiber because the story doesn't hang together well enough for there to be a story."
But there is still an argument for consuming dietary fiber, even when colorectal cancer is taken out of the picture, Park said.
"There are studies showing that dietary fiber reduces the risk of other disease, such as heart disease and diabetes, so people should continue to eat dietary fiber," she said.
The American Cancer Society can tell you more about colorectal cancer.