Psyllium reduces inulin-induced colonic gas production in IBS: MRI and in vitro fermentation studies

Objective Health-promoting dietary fibre including inulin often triggers gastrointestinal symptoms inpatients with IBS, limiting their intake. Our aim was to test if coadministering 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 500 mL test drink containing either inulin 20 g, psyllium 20 g, inulin 20 g+ psyllium 20 g or dextrose 20 g (placebo). Breath hydrogen was measured every 30 min with MRI scans hourly for 6 hours. Faecal samples from a subset of the patients with IBS were tested using an in vitro fermentation model. Primary endpoint was colonic gas assessed by MRI. Results Colonic gas rose steadily from 0 to 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 coadministrationto 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 coadministration (p=0.005). Breath hydrogen rose significantly from 120 min after inulin but not psyllium; coadministration of psyllium with inulin delayed and reduced the maximum increase, AUC((0-360 min)) from 7230 (3255-17910) ppm.hour to 1035 (360-4320) ppm.hour, 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 patients with IBS but does not directly inhibit fermentation. Whether coadministration with psyllium increases the tolerability of prebiotics in IBS warrants further study.