Soluble fibre supplementation with and without a probiotic in adults with asthma: A 7-day randomised, double blind, three way cross-over trial

Randomized, double-blind, 3-way cross-over trial in 17 adults with doctor-diagnosed stable asthma in Newcastle, Australia. Participants were on a fiber-controlled background diet, and treatment order was randomized by a 3 x 3 Latin square; 3 participants withdrew during the study.

This 3-way crossover trial tested oral inulin 6 g twice daily for 7 days per period, with a matching placebo capsule in the inulin-only arm. The combination arm used the same inulin regimen plus a daily probiotic capsule containing Lactobacillus acidophilus LA-5 7.5 billion CFU, Lactobacillus rhamnosus GG 8.75 billion CFU, and Bifidobacterium animalis subsp. lactis BB-12 8.75 billion CFU. Each treatment period was separated by a 2-week washout.

Overall, 7 days of soluble fiber did not change plasma short-chain fatty acids, and adding a probiotic did not provide extra clinical benefit. Inulin showed within-group improvements in asthma control and airway inflammation, with ACQ6 decreasing by 0.35 (p = 0.006), sputum eosinophils decreasing by 1.0 (p = 0.006), and sputum HDAC9 expression decreasing by 0.49 (p = 0.008), but between-group effects versus placebo were generally not significant. Total plasma SCFA change remained nonsignificant for inulin+probiotic versus placebo (18.7, 95% CI -14.5 to 51.9; p = 0.325), and lung function and PBMC HDAC/HAT measures did not improve. The probiotic arm increased B. adolescentis and B. longum abundance, but this did not translate into clear clinical benefit.

The trial was very small, with only 17 randomized participants and 3 withdrawals, and it was short at 7 days per treatment period. Most between-group comparisons were not significant, several outcomes were exploratory, and some analyses used fewer than 17 participants. Findings are also limited to adults with relatively stable asthma, many of whom were using inhaled corticosteroids, so generalizability and durability of benefit are uncertain.