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Is fiber useful to individuals with IBS?

Last updated on October 8, 2021

Is fiber useful to individuals with IBS?Q. Is fiber useful to individuals with irritable bowel syndrome?

A. The jury’s still out. Studies addressing the question have reached different conclusions, due both to problems in study design and to the variable nature of symptoms described as irritable bowel syndrome (IBS). One recent study is of particular interest.

The investigators, from McMaster University Medical Center in Ontario, Canada, used the so-called double-blind crossover. In this approach, neither investigators nor subjects know whether the fiber supplement or a placebo is being used, and all subjects are given supplements part of the time and a placebo for the rest of the time. This trial was extended over seven months, allowing time to examine longer term changes in symptoms.

Over a six-month period, subjects were given four cookies daily, containing either corn fiber or a placebo for 12 weeks at a time. Each trial was separated from the next by a “washout” period to allow any effects to erode. Subjects were asked to score symptoms on a questionnaire as they entered the trial and at four-week intervals thereafter. Pressure measurements to assess changes in motility were also taken.

Curiously, several problems, including pain severity, frequency and consistency of bowel movements, and other abdominal symptoms improved over time both with corn fiber and the placebo. Pain in the lower left side was the most frequent symptom reported. And in this study, the “placebo effect” (the likelihood of reduced symptoms even without the bran cookies) was greatest for pain.

But the reduction in symptoms tended to erode over time. A drop in colon pressure with fiber intake did occur, but not to a significant degree. Perhaps one reason for the failure to demonstrate benefit is that fiber would be more effective in relieving constipation. However, only one-third of the subjects reported bowel movements less than twice a week.

This was a small study; only nine patients completed the trial, which lasted seven months.

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