Plain language summary
A low FODMAP (Fermentable Oligosaccharides, Disaccharides, Monosaccharides and Polyols) diet is being increasingly recommended for the management of IBS. However, the FODMAP diet can be low in potential prebiotic and fermentable fibre which may have an adverse effect on gut bacteria diversity and other colonic health biomarkers. This study set out to identify how a low FODMAP diet affected the pH, short-chain fatty acid concentrations and bacterial abundance and diversity in comparison to a typical Australian diet. The randomised cross over study consisted of 27 IBS and 6 healthy subjects who were blinded to 21 days of a low FODMAP diet and then, following a washout period of 21 days following their usual diet they were crossed over to the typical Australian diet for 21 days. The study found increased faecal pH, similar short chain fatty acid concentrations, a greater microbial diversity and reduced bacterial abundancy in faecal samples whilst following the low FODMAP diet. It was concluded that caution should be used when reducing FODMAP intake in the long term and that a low FODMAP diet should not be recommended for asymptomatic populations.
Abstract
OBJECTIVE A low FODMAP (Fermentable Oligosaccharides, Disaccharides, Monosaccharides And Polyols) diet reduces symptoms of IBS, but reduction of potential prebiotic and fermentative effects might adversely affect the colonic microenvironment. The effects of a low FODMAP diet with a typical Australian diet on biomarkers of colonic health were compared in a single-blinded, randomised, cross-over trial. DESIGN Twenty-seven IBS and six healthy subjects were randomly allocated one of two 21-day provided diets, differing only in FODMAP content (mean (95% CI) low 3.05 (1.86 to 4.25) g/day vs Australian 23.7 (16.9 to 30.6) g/day), and then crossed over to the other diet with ≥21-day washout period. Faeces passed over a 5-day run-in on their habitual diet and from day 17 to day 21 of the interventional diets were pooled, and pH, short-chain fatty acid concentrations and bacterial abundance and diversity were assessed. RESULTS Faecal indices were similar in IBS and healthy subjects during habitual diets. The low FODMAP diet was associated with higher faecal pH (7.37 (7.23 to 7.51) vs. 7.16 (7.02 to 7.30); p=0.001), similar short-chain fatty acid concentrations, greater microbial diversity and reduced total bacterial abundance (9.63 (9.53 to 9.73) vs. 9.83 (9.72 to 9.93) log10 copies/g; p<0.001) compared with the Australian diet. To indicate direction of change, in comparison with the habitual diet the low FODMAP diet reduced total bacterial abundance and the typical Australian diet increased relative abundance for butyrate-producing Clostridium cluster XIVa (median ratio 6.62; p<0.001) and mucus-associated Akkermansia muciniphila (19.3; p<0.001), and reduced Ruminococcus torques. CONCLUSIONS Diets differing in FODMAP content have marked effects on gut microbiota composition. The implications of long-term reduction of intake of FODMAPs require elucidation. TRIAL REGISTRATION NUMBER ACTRN12612001185853.
Methodological quality
Allocation concealment
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No
