Introduction Dietary restriction of fermentable oligo-, di-, mono -saccharides and polyols (low FODMAP diet, LFD) is widely used for the management of irritable bowel syndrome (IBS), however it reduces gastrointestinal (GI) bifidobacteria. B-galacto-oligosaccharide (B-GOS; HOST-G904) are prebiotics that reduce symptoms and increase bifidobacteria in IBS however the combination of the two therapies has not previously been investigated.

Method This randomised controlled trial aimed to investigate whether: 1) IBS symptoms improved on LFD supplemented with B-GOS compared to control; and 2) B-GOS could prevent the reduction of GI bifidobacteria seen in patients following the LFD. Adults fulfilling Rome criteria for IBS were screened (n=130). Sixty-nine patients were recruited to a multicentre 3-arm parallel RCT and were randomised to: control (sham diet/placebo), LFD only (LFD/placebo) or LFD plus B-GOS (LFD/B-GOS) for four weeks. Validated questionnaires were used to assess GI symptoms at week 0 and week 4 and a stool sample collected for analysis at week 0, week 1 and week 4. Stool were analysed for bifidobacteria using fluorescent in situ hybridisation, and short-chain fatty acids (SCFA) and pH were measured using gas chromatography and pH probe respectively. Logistic regression, and ANOVA/ANCOVA (with post-hoc correction) were used to determine differences across the three groups.

Results At week 4 adequate relief of IBS symptoms differed significantly between control (30.4%), LFD (50%) and LFD/B-GOS (66.7%) (p=0.046), with post-hoc differences specifically between control and LFD/B-GOS (p=0.015). Individual IBS symptoms were more markedly improved in the LFD/B-GOS group compared to control. Bifidobacteria (log₁₀/g dry weight) also differed across the groups (control 9.8, LFD 9.6, LFD/B-GOS 9.5; p=0.009), with post-hoc differences between the LFD/B-GOS and control at week 4 (p=0.009) Higher stool pH, and lower butyrate at week 1 and week 4 were observed in the LFD vs control diet group. Similar differences were observed in the LFD/B-GOS vs control diet group although pH was not higher than control until week 4.

Conclusion Symptoms of IBS markedly improved during LFD supplemented with B-GOS prebiotic, suggesting a synergy between the two therapies. The LFD significantly impacts the GI luminal environment within the first seven days and these changes persist with diet restriction, however addition of a low dose prebiotic does not overcome the effect of diet on bifidobacteria.

Disclosure of Interest B. Wilson Conflict with: BW is the recipient of a PhD fellowship awarded by Clasado BioSciences., M. Rossi: None Declared, G. Parkes: None Declared, Q. Aziz: None Declared, S. Anderson: None Declared, P. Irving: None Declared, M. Lomer: None Declared, K. Whelan: None Declared