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

Randomized, double-blind, placebo-controlled, cross-over human intervention study in healthy adults from New Zealand. Participants were 19 to 65 years old with BMI 18.5 to 30 kg/m2, and were stratified by habitual dietary fibre intake into low-fibre (n 14) and high-fibre (n 20) groups; 34 participants were used in the prebiotic intervention analysis.

Participants received 16 g/day of an inulin-type fructan prebiotic (Orafti Synergy1, a 50:50 inulin-to-fructooligosaccharide mix) for 3 weeks, given as two 8 g doses per day. Each dose was mixed into a hot or cold beverage and taken 30 minutes before breakfast and 30 minutes before dinner in a randomized cross-over comparison with placebo, with a 3-week washout between phases.

Overall, the prebiotic produced a stronger gut microbiota response in participants with high habitual fibre intake than in those with low intake. In the whole cohort, Bifidobacterium increased significantly (P < 0.001), while Coprococcus (P = 0.016), Dorea (P = 0.029), Ruminococcus (Lachnospiraceae) (P = 0.007), and Oscillospira (P = 0.031) decreased; Faecalibacterium showed a nonsignificant upward trend (P = 0.088). In the high-fibre group, Bifidobacterium increased (P < 0.001) and Faecalibacterium increased (P = 0.010), with decreases in Coprococcus (P = 0.010), Dorea (P = 0.043), and Ruminococcus (P = 0.032). Moderate gastrointestinal symptoms were higher during the prebiotic phase than placebo in the whole cohort (P = 0.013), including more moderate flatulence (P = 0.012).

The analysis was small and short term, with only 34 participants evaluated over 3-week intervention periods. Subgroup findings by habitual fibre intake increase interpretive complexity, and the trial was conducted in healthy adults from one region, limiting generalizability. The prebiotic also increased gastrointestinal symptoms, which may affect tolerability despite microbiota benefits.