Psyllium reduces insulin-induced colonic gas production in irritable bowel syndrome: MRI and in vitro fermentation studies

Objective: Health promoting dietary fibre including inulin often triggers gastrointestinal symptoms in patients with irritable bowel syndrome (IBS), limiting their intake. Our aim was to test if co-administering psyllium with inulin would reduce gas production. Design: A randomised, four-period, four-treatment, placebo-controlled, crossover trial in 19 patients with IBS. Subjects ingested a 500ml test drink containing either inulin 20g, psyllium 20g, inulin 20g + psyllium 20g, or dextrose 20g (placebo). Breath hydrogen was measured every 30 minutes with MRI scans hourly for 6 hours. Faecal samples from a subset of the IBS patients were tested using an in vitro fermentation model. Primary endpoint was colonic gas assessed by MRI. Results: Colonic gas rose steadily from 0-6 hours, with inulin causing the greatest rise, median (IQR) AUC(0-360 min) 3145 (848-6502) ml.min. This was significantly reduced with inulin and psyllium co-administration to 618 (62-2345) ml.min (p=0.02), not significantly different from placebo. Colonic volumes AUC(0-360 min) were significantly larger than placebo for both inulin (p=0.002) and inulin and psyllium co-administration (p=0.005). Breath hydrogen rose significantly from 120 minutes after inulin but not psyllium; co-administration of psyllium with inulin delayed and reduced the maximum increase, AUC(0-360 min) from 7230 (3255-17910) ppm.hr to 1035 (360-4320) ppm.hr, p=0.007. Fermentation in vitro produced more gas with inulin than psyllium. Combining psyllium with inulin did not reduce gas production. Conclusions: Psyllium reduced inulin-related gas production in IBS patients but does not directly inhibit fermentation. Whether co-administration with psyllium increases the tolerability of prebiotics in IBS warrants further study.