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Dietary Fibre Questioned for Prevention of Colorectal Adenomas and Carcinomas: Presented at DDW

By Larry Schuster

SAN FRANCISCO, CA -- May 21, 2002 -- Two Canadian researchers are questioning whether dietary fibre is protective against the development of colorectal cancer.

Reporting here at Digestive Disease Week (DDW), the researchers said their doubts arose after they conducted a "systematic review and meta-analysis to assess the effect of dietary fibre on the incidence or recurrence of colorectal adenomas, the incidence of colorectal cancer, and the development of adverse events."

Co-investigators Tracey K. Asano, MD, and Robin S. McLeod, MD, of the University of Toronto, Ontario, Canada, noted that experimental evidence has supported the hypothesis that fibre may be protective. But their analysis finds no evidence that increased intake of dietary fibre reduces the incidence or recurrence of adenomatous polyps within two to four years.

The trials were identified from Medline, Embase, and the Cochrane Controlled Trials Register up to October 2001. Five studies (with a total of 4,349 patients) met the inclusion criteria: patients had no history of colorectal cancer, all had no polyps at baseline, and repeated visualizations of the colon/rectum were conducted after at least two years of follow-up. Two reviewers independently extracted data, assessed trial quality, and resolved discrepancies by consensus.

The primary outcomes were the number of patients with: (a) at least one adenoma, (b) more than one adenoma, (c) at least one adenoma greater than or equal to 1, cm or (d) a new diagnosis of colorectal cancer. The secondary outcome was the number of adverse events.

Patients in the intervention arms of the five studies were given wheat bran fibre, ispaghula husk, or a comprehensive dietary intervention with high-fibre whole food sources alone or in combination. There was no difference between the intervention and control groups for the number of patients with at least one adenoma (relative risk [RR] 1.04, 95 percent confidence interval [CI] 0.95,1.13; risk difference [RD] 0.01, 95 percent CI -0.02,0.04).

The combined results for the number of patients with more than one adenoma (RR 1.02, 95 percent CI 0.89,1.17; RD 0.00, -0.02,0.03) or at least one adenoma 1 cm or greater (RR 0.94, 95 percent CI 0.77,1.15; RD -0.01 -0.02,0.01) were not statistically significant.

Secondary outcome, other primary outcomes, and subanalyses by type of fibre were neither statistically nor clinically significant.

"There is currently no evidence from [randomised controlled trials] to suggest that increased dietary fibre intake will reduce the incidence or recurrence of adenomatous polyps" within four years, the researchers conclude.

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