High-Fiber Diets May Not Keep Colorectal Polyps Away
Volunteers for the Wheat Bran Fiber Study were also divided into two groups. For three years, one group consumed a high-fiber cereal (containing 13.5 grams of fiber) every day; the other group ate a low-fiber (2 grams) cereal. After two years, all the volunteers were allowed to get up to 25% of their daily fiber supplement from a fiber bar. Otherwise, they ate their usual diets, which were not low in fat.
Colonoscopy screenings found that 51.2% of those in the low-fiber group and 47% of those in the high-fiber group had new polyps.
"The bottom line, no matter how we looked at it, was there were no significant positive effects of wheat bran fiber on adenoma recurrence," says Maria Elena Martinez, PhD, an investigator in the Wheat Bran Fiber Study.
Still, researchers are not suggesting that people toss their bran muffins in favor of cheese omelets. "Don't give up on diet," Schatzkin says. "There's lots of evidence ... that adopting a diet that's low in animal fats and saturated fats, and high in whole grains and rich in fruits and vegetables, can improve overall health and reduce the risk of chronic disease. The problem is, we just have not yet been able to pin this down for colon cancer."
For colon cancer prevention, "screening is still going to be the No. 1 thing," Martinez tells WebMD. "I think the overall picture is that fiber does appear to prevent other important disease -- [heart] disease and diabetes. Giving up on fiber is not the right thing."
"These are beautifully done studies. Unfortunately, they don't answer all the questions," says Bernard Levin, MD, who reviewed the work for WebMD. "Is it possible that people who start this [diet] in their 20s and 30s would derive benefit? Secondly, [the studies] mostly address the issue of small polyps." Levin is vice president for cancer prevention at the University of Texas MD Anderson Cancer Center in Houston.
These studies did have limits. For example, neither could examine whether eating a healthier diet or extra fiber would affect either the progression of polyp growth or the tendency of polyps to become cancerous. Also, both studies followed the subjects for only a few years. The two research groups intend to follow the volunteers for several more years.
While Levin is disappointed in the studies' results, he tells WebMD: "We should not go overboard and say everyone can go out and eat hamburgers and grilled cheese sandwiches. I think one should be moderate and say these diets have benefits for other health purposes."