The role of fiber supplementation in the treatment of irritable bowel syndrome

Irritable bowel syndrome (IBS) is a functional bowel disorder associated with a wide variety of clinical symptoms. The use of fiber in treatment of IBS is well established, but recent reviews have shown conflicting evidence. The aim of our review was to study the effects of fiber (soluble and insoluble) on the symptoms of IBS. Medline, EMBASE, Cochrane Central, CINAHL, LILACS, and ClinicalTrials.gov were searched for appropriate studies. Two reviewers screened the title/abstract and full text against the inclusion criterion - that is, randomized control trials/crossover studies that compare fiber with placebo for its effect on IBS in an outpatient setting. Independent double data extraction was performed across multiple fields. An assessment of the risk of bias and tests for heterogeneity were carried out, along with a meta-analysis of the outcomes of interest. The search yielded 4199 unique records: 121 were selected after title/abstract screening and 22 after full screening. There was moderate clinical, methodological, and statistical heterogeneity across studies, with a moderate risk of bias. Overall, there was a significant improvement in global assessment of symptoms among those randomized to fiber [risk ratio: 1.27; 95% confidence interval (CI): 1.05-1.54]. Soluble fiber improved assessment of symptoms (risk ratio 1.49; 95% CI: 1.09-2.03), as well as the abdominal pain score (mean difference: -1.84; 95% CI: -2.72 to -0.97), with insoluble fiber not showing improvement in any outcome. Soluble fiber appears to improve symptoms of IBS, whereas there is no evidence for recommending insoluble fiber for IBS.