Longitudinal study of gut microbiome in obsessive–compulsive disorder

INTRODUCTION: Patients with obsessive–compulsive disorder (OCD) often have limited exposure to a diverse environment and perform repetitive compulsions such as excessive cleaning and washing, which could lead to altered gut microbiome. Therefore, longitudinal studies that investigate changes in gut microbiome before and after cognitive behavioral therapy based on exposure and response prevention (ERP) are warranted. METHODS: All study participants (N = 64) underwent a structured psychiatric diagnostic interview prior to inclusion. Nutritional intake was assessed with a comprehensive food frequency questionnaire. Stool samples were collected from OCD patients before ERP (n = 32) and 1 month after completion of ERP (n = 15), as well as from healthy controls (HCs; n = 32). Taxonomic and functional analyses were performed using data from microbiome whole genome sequencing. RESULTS: Patients with OCD at baseline reported consuming significantly less fiber than HCs (R (2) = .12, F(2, 59) = 5.2, p ≤ .01). There were no significant differences in α‐ and β‐diversity indices, or taxonomic dissimilarities at the species level between patients with OCD and HCs, or within patients before and after ERP. Functional profiling based on gut microbial gene expression was grouped into 56 gut–brain modules with neuroactive potential. None of the gut–brain modules differed significantly in expression between patients with OCD at baseline and HCs or within patients before and after ERP. CONCLUSIONS: The diversity, composition, and functional profile of the gut microbiome in patients with OCD did not differ significantly from HCs and remained stable over time, despite behavioral changes.