Baseline Dietary Fiber Intake and Colorectal Adenoma Recurrence in the Wheat Bran Fiber Randomized Trial

Abstract

The Wheat Bran Fiber (WBF) trial was a double-blind, high-fiber versus low-fiber phase III intervention trial in which participants were randomly assigned to receive a cereal fiber supplement of either 2.0 g/day or 13.5 g/day to assess whether a high-fiber supplement could decrease risk of recurrent colorectal adenomas. Although no effect of the supplement on polyp recurrence was observed, participants consumed a baseline average of 17.5 grams of fiber per day, which may have been sufficient to protect against adenoma recurrence. Therefore, we examined whether baseline fiber intake affected colorectal adenoma recurrence or modified the effect of treatment group in the WBF trial participants. Quartiles of baseline fiber intake were calculated on the basis of the distribution in the study population. Odds ratios (ORs) for adenoma recurrence were calculated using the lowest quartile of fiber intake as the reference. The effect of fiber from specific food sources on adenoma recurrence was also assessed. All statistical tests were two-sided. Adjusted ORs (95% confidence intervals) for adenoma recurrence were 0.79 (0.56 to 1.12), 0.76 (0.54 to 1.08), and 0.83 (0.57 to 1.19) for the second, third, and fourth quartiles, respectively. Fiber from the three primary food sources (fruits; breads, cereals and crackers; and vegetables) had no appreciable effect on adenoma recurrence. Baseline fiber intake also had little effect on adenoma recurrence when the population was stratified by treatment group. In addition, there was no interaction between treatment group and quartile of baseline fiber intake. No association was found between amount of fiber consumed at baseline and adenoma recurrence in the WBF trial participants. The baseline fiber intake, whether considered as a whole or from specific sources, did not modify the effect of treatment group.