A randomised, placebo-controlled trial in healthy humans of modified cellulose or psyllium evaluating the role of gelation in altering colonic gas production during inulin co-administration.

Psyllium significantly reduced initial breath hydrogen production compared to placebo when co-administered with inulin.

• A randomised, three-way, placebo-controlled non-inferiority study was conducted with healthy volunteers (n = 30).
• Fermentation in vivo was assessed by breath hydrogen measurements for 24 hours after ingestion.
• The control comparator was maltodextrin (placebo).
• Psyllium co-administration with inulin reduced initial breath hydrogen production compared to the placebo condition.

Methylcellulose did not demonstrate non-inferiority to psyllium in reducing initial breath hydrogen production.

• Despite development of a methylcellulose formulation with comparable rheological and inulin release behaviour to psyllium in vitro, non-inferiority in vivo was not demonstrated.
• The primary outcome measure was reduction in initial breath hydrogen production.
• The trial used a three-way crossover design comparing psyllium, methylcellulose, and maltodextrin placebo.

Psyllium and methylcellulose hydrogels exhibited different gastrointestinal transit behaviour despite similar physicochemical properties.

• Transit behaviour was assessed based on breath hydrogen time to rise >10 ppm and time to peak.
• Despite comparable rheological properties and inulin release behaviour in vitro, the two fibres showed distinct in vivo transit characteristics.
• The authors hypothesise that psyllium's polysaccharide network 'self-healing' properties after deformation by intestinal pressure waves may underpin its effectiveness.

A methylcellulose formulation with comparable rheological and inulin release behaviour to psyllium was successfully developed in vitro.

• Methylcellulose is a physically cross-linked fibre ingredient widely used in food production for its tunability and affordability.
• The formulation was developed to match psyllium's in vitro properties before proceeding to clinical testing.
• Both psyllium and methylcellulose form physically cross-linked gels hypothesised to resist gastrointestinal shear forces and impair microbial access to inulin.

The proposed mechanism by which psyllium delays inulin fermentation involves its gel physically impeding microbial access to inulin.

• The authors hypothesise that psyllium polysaccharides' physically cross-linked gel resists gastrointestinal shear forces and impairs microbial access to inulin, thereby delaying fermentation.
• Slowing rapid fermentation decreases colonic distention and reduces symptoms, allowing for better tolerance of prebiotics.
• The fast reformation or 'self-healing' properties of psyllium's polysaccharide network after deformation by intestinal pressure waves is hypothesised to underpin its effectiveness compared to methylcellulose.

Co-administration of psyllium with inulin has previously been shown to reduce gas production in irritable bowel syndrome patients compared to inulin alone.

• Prior work in IBS patients demonstrated that psyllium co-administration with inulin reduces gas production.
• The underlying mechanism of this effect was described as unclear, motivating the current study.
• The current study extended this investigation to healthy volunteers using a placebo-controlled design.