Lack of effect of a high-fiber cereal supplement on the recurrence of colorectal adenomas. Phoenix Colon Cancer Prevention Physicians' Network.

Randomized, double-blind, multicenter trial in adults aged 40 to 80 years with one or more histologically confirmed colorectal adenomas removed within the prior 3 months. In the active high-fiber arm, 802 participants were randomized and 719 completed; the low-fiber comparison arm had 627 randomized and 584 completed.

Oral wheat-bran cereal supplement taken daily for 3 years. The high-fiber regimen provided 13.5 g/day of wheat-bran fiber, while the comparison regimen provided 2 g/day.

High-fiber wheat-bran cereal did not reduce recurrence of colorectal adenomas. By last follow-up, recurrent adenomas were seen in 47.0% (338/719) of the high-fiber group versus 51.2% (299/584) of the low-fiber group, with an adjusted odds ratio of 0.88 (95% CI, 0.70 to 1.11; P=0.28). Recurrence by number of adenomas was also null (relative risk 0.99, 95% CI 0.71 to 1.36; P=0.93). Gastrointestinal symptoms were more common in the high-fiber group, including abdominal pain, diarrhea, intestinal gas, and bloating.

The trial did not show a statistically significant benefit and the confidence intervals allow only modest effects in either direction. Follow-up was variable, with median observation periods of 34 months in the high-fiber group and 36 months in the low-fiber group, and not all randomized participants completed follow-up. The modified allocation ratio and frequent gastrointestinal side effects may also affect interpretability and adherence.