High-than-average fiber consumption does not affect results of wheat bran fiber trial

The higher-than-average amount of dietary fiber consumed by participants in the Wheat Bran Fiber (WBF) trial even before they began taking fiber supplements did not account for the results of the trial, which found that fiber intake does not affect the recurrence rate of polyps in the colon. This new analysis appears in the November 6 issue of the Journal of the National Cancer Institute.

Anecdotal evidence has suggested that people who eat high-fiber diets have a lower incidence of colorectal cancer. The WBF trial compared the recurrence rate of adenomatous polyps (abnormal growths in the colon that are considered precursors of colon cancer) among people who were randomly assigned to receive a high-fiber dietary supplement (13.5 g/day) versus a low-fiber dietary supplement (2.0 g/day). The investigators found no difference in the recurrence rate of polyps between the two groups.

But because participants in the WBF trial consumed higher-than-average amounts of fiber compared with the general U.S. population (17.5 grams/day versus 14.8 grams/day), some scientists suggested that these participants had adequate protection from colorectal cancer recurrence even without the addition of a high-fiber supplement. In other words, the beneficial effects of supplemental fiber might be apparent only in participants who had lower baseline fiber intakes.

To see whether this was the case, Elizabeth T. Jacobs, Ph.D., of the Arizona Cancer Center, and her coworkers separated the participants into four groups based on their baseline fiber consumption and calculated the risk of polyp recurrence in each group. They also looked at the effect of baseline intake of fiber from specific food sources on polyp recurrence.

Baseline fiber intake did not appear to be associated with polyp recurrence. There was also no association between baseline intake of fiber from the three leading sources of dietary fiber (fruits; breads, cereals, and crackers; and vegetables) and polyp recurrence. Moreover, baseline fiber intake had no effect on polyp recurrence within each treatment group.

Contact: Rob Raine, Arizona Cancer Center, 520-626-4413; fax: 520-626-8606, rraine@azcc.arizona.edu.

Jacobs E, Giuliano A, Roe D, Guillén-Rodruiguez J, Alberts D, Martinez M. Baseline dietary fiber intake and colorectal adenoma recurrence in the wheat bran fiber randomized trial. J Natl Cancer Inst 2002;94:1620–5.

Note: The Journal of the National Cancer Institute is published by Oxford University Press and is not affiliated with the National Cancer Institute. Attribution to the Journal of the National Cancer Institute is requested in all news coverage.

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