Effects of dietary FODMAP content on the faecal microbiome and gastrointestinal physiology in healthy adults: a randomised, controlled cross-over feeding study

Abstract

The effect dietary FODMAPs (fermentable oligo-, di- and mono-saccharides and polyols) in healthy adults is poorly documented. This study compared specific effects of low and moderate FODMAP intake (relative to typical intake) on the faecal microbiome, participant-reported outcomes and gastrointestinal physiology. In a single-blind cross-over study, 25 healthy participants were randomised to one of two provided diets, ‘low’ (LFD) <4 g/d or ‘moderate’ (MFD) 14-18 g/d, for 3 weeks each, with ≥2-week washout between. Endpoints were assessed in the last week of each diet. The faecal bacterial/archaeal and fungal communities were characterised in 18 participants in whom high quality DNA was extracted by 16S rRNA and ITS2 profiling, and by metagenomic sequencing. There were no differences in gastrointestinal or behavioural symptoms (fatigue, depression, anxiety), or in faecal characteristics and biochemistry (including short-chain fatty acids). Mean colonic transit time (telemetry) was 23 (95% confidence interval: 15, 30) h with the MFD compared with 34 (24, 44) h with LFD (n=12; p=0.009). Fungal diversity (richness) increased in response to MFD, but bacterial richness was reduced, coincident with expansion of the relative abundances of Bifidobacterium, Anaerostipes, and Eubacterium. Metagenomic analysis showed expansion of polyol-utilising Bifidobacteria, and Anaerostipes with MFD. In conclusion, short-term alterations of FODMAP intake are not associated with symptomatic, stool or behavioural manifestations in healthy adults, but remarkable shifts within the bacterial and mycobiome populations were observed. These findings emphasise the need to quantitatively assess all microbial Domains and their interrelationships to improve understanding of consequences of diet on gut function.