Habitual dietary fibre intake influences gut microbiota response to an inulin-type fructan prebiotic: a randomised, double-blind, placebo-controlled, cross-over, human intervention study

Design: randomized, double-blind, placebo-controlled, cross-over trial. Participants: healthy adults aged 19–65 years, BMI 18.5–30 kg/m2, mixed gender. Habitual dietary fibre intake categorized as low (LDF) or high (HDF). Of 44 eligible, 34 completed the prebiotic phase (LDF n=14, HDF n=20); data from 33 participants were available for placebo analyses.

Prebiotic: 16 g/day inulin-type fructan (split into two 8 g doses), taken 30 minutes before breakfast and 30 minutes before dinner, mixed into hot or cold beverages, for 3 weeks. Placebo: 16 g/day maltodextrin, split into two 8 g doses, same timing and method, for 3 weeks.

Inulin-type fructan prebiotic increased Bifidobacterium in both LDF (P=0.001) and HDF (P<0.001). In HDF, Faecalibacterium increased (P=0.010) and Coprococcus (P=0.010), Dorea (P=0.043) and Ruminococcus (Lachnospiraceae) (P=0.032) decreased. No significant changes in overall SCFA concentrations. At genus level, LDF showed Bifidobacterium increase only; HDF showed additional Faecalibacterium increase and reductions in Coprococcus, Dorea and Ruminococcus; Lactobacillus increased in the HDF group. Inter-individual variability was high. Appetite changes occurred mainly in the HDF group (reduced hunger after lunch; increased fullness after lunch); GI symptoms were more frequent (moderate flatulence) in HDF during prebiotic. Conclusion: Habitual dietary fibre intake modulates gut microbiota responsiveness to an inulin-type fructan prebiotic; higher habitual fibre intake may confer greater microbial and appetite-related benefits when using this prebiotic; plan future interventions accordingly.

Small sample size; short duration; cross-over design with potential carryover; healthy population limits generalizability to disease states; uneven LDF (n=14) vs HDF (n=20) groups; only inulin-type fructan tested; no long-term health outcomes measured; high inter-individual variability.