Metagenomic sequencing of stool samples from healthy human volunteers from the EON study

Background: Recent studies show that colonic gas after ingestion of inulin can be reduced by co-administering psyllium.Objective: We aimed to determine if slowing delivery of inulin to the colon by administering it in divided doses would mimic the effect of psyllium.Methods: Healthy adults (n=17) were randomised to a single-blind, 3-arm, crossover trial. All consumed 20g inulin(I) powder dissolved in 500mL water and mixed with either 1) 20g psyllium husk (PI) or 2); 20g Maltodextrin (placebo) (MI) consumed as a single dose, or 3) 62.5ml divided doses of inulin(DI) given every 45 minutes over 6 hours. Breath Hydrogen (BH2) was measured over 24 hours, and stool microbiota was analysed using shotgun metagenomics.Results: [mean(SD)] DI and PI significantly reduced area under the curve (AUC) BH2 0-360 mins compared to MI, p<0.001. AUC(0-6h) being (6199.4+/-2889.2) after DI and (6855+/-5137) after PI, significantly less than MI (9970.6 +/- 3102.7). This was associated with a significant increase in BH2 for both DI and PI during the evening from 360-720 (p=0.014) and overnight 720-1320 (p=0.002). Furthermore, there was an additional significant increase overnight in BH2 for DI compared to psyllium, DI=30423+/-15406, PI= 5671+/-4711 p<0.001. Those failing to show a fall in BH2 AUC0-6h with psyllium showed greater release of arabinose during in vitro fermentation. Metagenomic analysis identified two species abundantly expressed in non-responders, Clostridium spp. AM22_11AC and Phocaeicola dorei which are also correlated with BH2 production for PI treatment. Dietary FODMAP intake correlated inversely with BH2 AUC0-24h on psyllium and correlated with stool microbiome.Conclusion: Divided administration of inulin mimics the effect of psyllium by reducing initial BH2 0-360 mins. BH2 is influenced by habitual dietary FODMAP intake, most likely due to associated changes in microbiome. Psyllium acts by both delaying transit to the colon and reducing colonic fermentation however degradation of psyllium by colonic microbiota may limit its effectiveness.