Mode of Action of Psyllium in Reducing Gas Production from Inulin and its Interaction with Colonic Microbiota: A 24-hour, Randomized, Placebo-Controlled Trial in Healthy Human Volunteers

Background Recent studies show that the increase in breath hydrogen (BH2) and symptoms after ingestion of inulin are reduced by coadministering psyllium (PI). Objectives To determine if slowing delivery of inulin to the colon by administering it in divided doses would mimic the effect of PI. Primary endpoint was the BH2 area under the curve AUC0–24 h. Secondary endpoints included BH2 AUC0–6 h, 6–12 h, and 12–24 h. Exploratory endpoints included the correlation of BH2 AUC0–24 h with dietary fermentable oligo-, di-, monosaccharides, and polyols (FODMAPs) intake and in vitro fermentation results. Methods A total of 17 healthy adults were randomly assigned to a single-blind, 3-arm, crossover trial. All consumed 20 g inulin (I) powder dissolved in 500 mL water and mixed with either 20 g maltodextrin (control) or 20 g PI consumed as a single dose or 20 g inulin given in divided doses (DDI), 62.5 mL every 45 min over 6 h. Twenty-four-hour BH2, dietary FODMAP intake, stool microbiota, and gas production in vitro were measured. Responders were defined as those whose AUC0–24 h BH2 was reduced by PI, whereas nonresponders showed no reduction. Results Compared with control, PI did not reduce mean BH2 AUC0–24 h, whereas DDI increased it, P < 0.0002. DDI and PI both significantly reduced BH2 AUC0–6 h compared with the control, P < 0.0001. However, subsequently, DDI significantly increased BH2 from 6 to 12 h (P < 0.0001) and overnight (12–24 h) (P < 0.0001), whereas PI did so only overnight (P = 0.0002). Nonresponders showed greater release of arabinose during in vitro fermentation and higher abundance of 2 species, Clostridium spp. AM22_11AC and Phocaeicola dorei, which also correlated with BH2 production on PI. Dietary FODMAP intake tended to correlate inversely with BH2 AUC0–24 h (r = −0.42, P = 0.09) and correlated with microbiome community composition. Conclusions DDI, like PI, reduces early BH2 production. PI acts by delaying transit to the colon but not reducing colonic fermentation over 24 h. Dietary FODMAP intake correlates with BH2 response to inulin and the microbiome.