Functional gastrointestinal disorders in 35 447 adults and their association with body mass index

Summary Background Functional gastrointestinal disorders’ ( FGID s) associations with body mass index ( BMI ) have not been thoroughly investigated in the general population. Aim To investigate the overlap between functional dyspepsia ( FD y), irritable bowel syndrome ( IBS ), functional constipation ( FC ) and functional diarrhoea ( FD h) and the relationship between BMI and those diagnoses in a large French adult population. Methods Subjects participating in the Nutrinet‐Santé cohort study completed a questionnaire based on Rome III criteria. Anthropometrics, socio‐demographical and lifestyle data were collected via self‐administered questionnaires. Associations between BMI and FGID s were investigated with multivariate logistic regression. Results A total of 35 447 subjects were included in the analysis. Among subjects with FGIDs, 10.4% presented more than one disorder. [ FD y coexisted with IBS (23.6%) and FC (15.1%)]. Associations between BMI and FD y differed according to sex. In females, higher odds were observed for underweight and obesity subgroups ( OR  = 1.26 (95% CI: 0.99–1.59), OR  = 1.35 (1.08–1.69), OR  = 1.20 (0.81–1.77), OR  = 1.47 (0.89–2.42) for underweight, class I, II and III obesity respectively compared with normal BMI ), forming a U‐shaped relationship confirmed with nonlinear model ( P  < 0.001). In females, FD h was associated with BMI [ OR  = 1.05 (1.03–1.07), P  < 0.001]. In males, a negative association between BMI and IBS was observed [ OR  = 0.97 (0.94–0.99), P =0.04]. Other associations were not significant. Conclusions Our study showed an important overlap in FGID s, supporting the contention of common pathophysiological mechanisms. Relationships between BMI and FGID s appeared to be sex‐dependent. Interaction by sex in the association between BMI and FGID s should therefore be further explored.