Psyllium Increases Colonic Volumes Without Increasing Colonic Gas or Breath Hydrogen

Psyllium (ispaghula) husk in wooden bowl on rustic background. Top view with copy space
Investigators tested the hypothesis that psyllium can reduce the increase in colonic gas induced by inulin in patients with IBS.

Psyllium reduces inulin-related gas production in patients with irritable bowel syndrome (IBS) but does not directly inhibit fermentation, according to a study in Gut.

Investigators used magnetic resonance imaging (MRI) to test the hypothesis that psyllium can reduce the increase in colonic gas induced by inulin in patients with IBS. In the single-center, 4-period, 4-treatment, placebo-controlled, crossover trial, participants received each treatment once in randomized order. The treatments were test drinks containing 20 g inulin powder, 20 g psyllium powder, 20 g inulin powder and 20 g psyllium powder, and 20 g dextrose powder as a placebo control.

The researchers conducted MRI scans immediately after the drink and then hourly for 6 hours; hydrogen breath tests and symptom scoring were also performed every half-hour. The study authors tested fecal samples from a subset of patients with IBS using an in vitro fermentation model. The change from fasting values in colonic gas assessed using the area under the curve (AUC) from 0 to 360 min in arbitrary units was the primary endpoint.

A total of 26 patients attended the initial screening visit, and 19 (median age, 39; range, 19-65 years; 15 women) completed the study.

Colonic gas increased steadily and reached a maximum at 360 min. The AUC of the change in colonic gas from fasting to 360 min was significantly affected by the fiber that was given (Friedman test, P =.005). Inulin caused the greatest increase in colonic gas (AUC gas, 3145 mL/min), which was reduced significantly by the coadministration of inulin and psyllium (AUC, 618 mL/min; P =.02), with the latter not significantly different from dextrose (P >.99).

Total colonic volume was unaffected by dextrose and increased steadily for psyllium alone and inulin alone, but the largest increase occurred with inulin and psyllium coadministration. Repeated measures of 1-way analysis of variance revealed a significant difference among test drinks (P =.01). Post-hoc analyses demonstrated greater AUCs for inulin (353.8±85.0 L/min) and inulin and psyllium coadministration (362.5±109.0 L/min) vs dextrose (300.2±73.0 L/min; P =.002 and P =.005, respectively).

The researchers observed significant differences in AUC breath hydrogen among the test drinks (P <.0001). Post-hoc analysis revealed that AUC for breath hydrogen after inulin (7230 ppm/h) was significantly greater than after psyllium (555 ppm/h; P <.0001) and dextrose (750 ppm/h; P <.0001).

The coadministration of inulin and psyllium decreased the AUC to 1035 ppm/h, which was significantly lower than that for inulin alone (P =.0065). No differences were observed in AUC for breath hydrogen regarding IBS subtypes for any of the test drinks.

“Our small mechanistic study has demonstrated that adding psyllium to inulin reduces gas production in patients with IBS and suggests that by choosing diets with adequate amounts of viscous fiber, patients may be able to obtain the prebiotic health benefits of high-fiber diets without exacerbating their IBS symptoms, particularly flatulence,” the researchers commented.

Disclosure: Some of the study authors declared affiliations with pharmaceutical companies and other companies. Please see the original reference for a full list of authors’ disclosures.


Gunn D, Abbas Z, Harris HC, et al. Psyllium reduces inulin-induced colonic gas production in IBS: MRI and in vitro fermentation studies. Gut. Published online August 5, 2021. doi: 10.1136/gutjnl-2021-324784