A randomized, placebo-controlled, crossover trial investigated whether coadministration of psyllium with inulin – a dietary fibre – could reduce gastrointestinal symptoms in IBS patients. A total of 19 participants with either constipation- or diarrhea-predominant IBS were instructed to consume a low-fibre, low-FODMAP diet one day prior to the study to limit food intake that might increase colonic gas. Participants were administered a one-time 500 mL test drink containing either (1) 20 g inulin, (2) 20 g psyllium, (3) 20 g inulin and psyllium, or (4) 20 g dextrose powder to be used as a placebo control. Colonic gas was measured with hourly MRI scans for the 6-hour period. Authors also measured breath hydrogen every 30 minutes and collected stool samples to test for fermentation and viscosity in a separate in vitro study on laboratory models. Inulin was found to cause the highest rise of median colonic gas (3145 mL) in the 6-hour timeframe, compared to the significant reduction when inulin and psyllium were co-administered (618 mL). Breath hydrogen significantly increased from 120 min with inulin but not psyllium administration, while co-administration reduced and delayed an increase. Fermentation results from the in vitro study reported higher gas production with inulin alone compared to the psyllium-inulin combination, suggesting that psyllium coadministration with inulin can reduce inulin-related gas production in IBS patients.