Fiber supplementation in irritable bowel syndrome: a systematic review and meta-analysis of randomized controlled trials
Psyllium fiber modestly increases global symptom response in irritable bowel syndrome.
*Systematic review and meta-analysis of randomized trials; Level 1a (OCEBM).
Citation
Staudacher HM, Rucco V, Mancell S, Dimidi E, Whelan K. Fiber supplementation in irritable bowel syndrome: a systematic review and meta-analysis of randomized controlled trials. Gastroenterology. 2026. doi:10.1053/j.gastro.2026.07.027
Background
Fiber supplements are widely recommended for irritable bowel syndrome, but prior summaries were more than 10 years old. This review tested whether newer evidence still supports fiber, and which fiber types help most.
Patients
Adults with irritable bowel syndrome in 30 trials, totaling 1,904 participants. Trials excluding isolated fiber effects, high-fiber diets, synbiotics, symptom-challenge studies, or patients with other gastrointestinal diseases were not eligible.
Intervention
Fiber supplements, most commonly wheat bran, psyllium, inulin-type fibers, and beta-galacto-oligosaccharides.
Control
Placebo-like controls matched as closely as possible to isolate the fiber effect.
Outcome
Clinical response, overall symptoms, abdominal pain, bloating, gas, stool measures, and quality of life. One response definition used the Irritable Bowel Syndrome Symptom Severity Score (0–500).
Follow-up Period
7 days to 3 months.
Results
| Outcome | Key finding |
|---|---|
| Clinical response (primary) | 52% with fiber versus 44% with control; RR 1.21 (95% CI 1.03 to 1.41); NNT 13. |
| Psyllium response | RR 1.53 (95% CI 1.06 to 2.19). |
| Overall symptoms with beta-galacto-oligosaccharides | Standardized mean difference -0.62 (95% CI -1.16 to -0.09). |
RR=risk ratio; NNT=number needed to treat; CI=confidence interval; OCEBM=Oxford Centre for Evidence-Based Medicine.
No significant improvement was found for abdominal pain, bloating, gas, stool consistency, or quality of life overall. Wheat bran did not improve response. Clinical response analyses used intention-to-treat methods, counting withdrawals as nonresponders.
Limitations
No trial was low risk of bias, and psyllium evidence mostly came from high-risk trials. Reporting by irritable bowel syndrome subtype was limited, so results may not apply equally to constipation- or diarrhea-predominant patients. Adverse events and adherence were incompletely reported. Some publication bias was suggested for clinical response.
Funding
No review funding; author disclosures include nutrition-industry ties.
Clinical Application
Offer psyllium as first-line fiber therapy; avoid recommending wheat bran specifically for symptom relief.
Discussion
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In this systematic review/meta-analysis of placebo-controlled RCTs, fiber supplementation increased IBS clinical response (52% vs 44%; RR 1.21, 95% CI 1.03–1.41), especially psyllium (RR 1.53). Given risk of bias, heterogeneity, and limited IBS-subtype data, would you change practice? In this meta-analysis, 52% of patients receiving fiber had clinical response versus 44% receiving control, with RR 1.21. Which statement best distinguishes the relative and absolute effects?