Clinical Trial: Randomised Placebo-Controlled Trial of Methylcellulose and Psyllium Gels on Inulin-Induced Colonic Gas.

In 30 seconds

This three-way randomised crossover trial compared methylcellulose, psyllium and maltodextrin placebo, each given with inulin, in 22 healthy volunteers. MRI and breath hydrogen measurements assessed intestinal water, fibre and gas. Neither gel significantly changed overall colonic gas exposure across 0–360 minutes, but both were associated with less gas after reaching the colon (AUC 180–360 min, p = 0.02). Methylcellulose increased small- and large-bowel water measures more than psyllium. The findings suggest a possible mechanism for improving tolerance of fermentable carbohydrates, but the study did not test this in people with IBS.

Key findings

• Methylcellulose and psyllium were associated with less colonic gas after reaching the colon (AUC 180-360 min, p = 0.02), without significantly altering AUC 0-360 min.
• Both gels increased small-bowel free water; the increase was greater with methylcellulose than psyllium (p = 0.0005).
• Both gels increased colonic chyme wateriness and hydrated fibre volume; both measures were greater with methylcellulose than psyllium (p = 0.01 and 0.02, respectively).
• Breath hydrogen over 24 hours did not differ between groups (AUC 0-24 h, p = 1.0); psyllium reduced it during 0-6 hours (p = 0.008).

Why it matters

The trial provides physiological evidence that gel-forming fibres can alter intestinal water and reduce inulin-associated colonic gas after reaching the colon. Methylcellulose produced larger water-related effects than psyllium, which may be relevant to the hypothesis that fibre gels could help some people tolerate FODMAPs. However, these outcomes were measured in healthy volunteers, not patients experiencing IBS symptoms.

What to keep in mind

The study involved 22 healthy volunteers and assessed physiological responses to a single inulin challenge; it did not establish symptom benefit or tolerability in people with IBS.