Gastrointestinal complaints after Roux-en-Y gastric bypass surgery. Impact of microbiota and its metabolites.

Unexplainable gastrointestinal complaints occasionally occur after Roux-en-Y Gastric Bypass (RYGB) surgery. We therefor investigated the impact of microbiota composition and metabolites on gastrointestinal complaints after RYGB. In the BARICO study (Bariatric surgery Rijnstate and Radboudumc neuroimaging and Cognition in Obesity), microbiota and metabolites were measured before surgery, and 6, and 24 months after surgery. Gastrointestinal complaints were assessed with the Irritable Bowel Syndrome Severity Scoring System (IBS-SSS) questionnaire 24 months after surgery. 65 participants (86.2 % female) with a mean age of 46.2 ± 6.0 years, and mean BMI of 41.2 ± 3.6 kg/m² were included. According to the IBS-SSS questionnaire, 32.3 % had moderate/severe gastrointestinal complaints 24 months after surgery. Microbiota alpha diversity remained stable, while beta diversity significantly changed over time. Bile acids and short-chain fatty acids were significantly higher, and inflammatory markers significantly lower after surgery. Barnesiella sp., Escherichia/Shigella sp., and Faecalibacterium prausnitzii correlated positively, while Akkermansia sp correlated inversely with gastrointestinal complaints. Patients with mild and moderate/severe gastrointestinal complaints showed higher levels of GLC-3S. These findings suggest involvement of microbiota and metabolite changes in gastrointestinal complaints after surgery. However, it remains unclear whether bacteria influence gastrointestinal complaints directly or indirectly. Further exploration is required for development of interventions against gastrointestinal symptoms after surgery.