Severe obesity, a susceptibility factor for developing inflammatory bowel disease. Results of a population-based study.

Background And Aims: Inflammatory bowel disease (IBD) develops in genetically susceptible individuals exposed to certain environmental factors, of which only a few have been established. We aimed to assess whether bariatric surgery (BS) and severe obesity are associated with an increased risk of developing IBD.

Methods: Adults diagnosed with obesity or severe obesity between 2005 and 2020 were identified from the Catalan Health Surveillance System; those diagnosed with IBD prior to the diagnosis of obesity or severe obesity were excluded. Individuals who had undergone BS and those with a new diagnosis of IBD were identified and their likelihood of developing IBD was analysed.

Results: A total of 93,473 individuals with severe obesity, 1,009,256 with obesity and 14,698 who underwent BS were identified. The incidence rates of IBD among individuals who had undergone BS prior to IBD diagnosis was 0.84 cases per 1000 person-years, 0.90 cases per 1000 person-years among individuals with severe obesity without BS and 0.60 cases per 1000 person-years in individuals with obesity. In the multivariable regression analysis, severe obesity (HR 1.46; 95%CI 1.31-1.62), BS (HR 1.57; 95%CI 1.25-1.97) and smoking habit (HR 1.57; 95%CI 1.46-1.69) were risk factors for developing IBD (as well as for Crohn's disease and ulcerative colitis). Conclusions: Severe obesity and BS were independent risk factors for the development of IBD. Non-invasive screening for IBD seems to be warranted in this population.