Background: The frequency of obesity and possible correlations with characteristics and outcome of inflammatory bowel disease (IBD) are undefined. Primary aim was to assess the Body Mass Index (BMI) distribution in IBD patients in follow-up. Secondary aim was to compare clinical characteristics and course of IBD in normal weight versus overweight or obese patients.

Methods: Adult IBD patients in regular follow-up were prospectively enrolled and BMI was recorded during outpatient visits. Comparisons were assessed by Student t-test, Mann-Whitney u-test and Chi-square test, as appropriate.

Results: In the 300 IBD patients enrolled (150 Crohn's Disease, CD, 150 Ulcerative Colitis, UC), BMI distribution included: 16 (5.3%) underweight, 170 (56.7%) normal weight, 92 (30.7%) overweight, 22 (7.3%) obese patients. For the secondary aim, the 16 underweight patients were excluded, thus leaving 284 patients for the analysis (141 [49.6%] CD; 143 [50.4%] UC). Among these, 114 (40.2%) were overweight/obese and 170 (59.8%) normal weight. CD group included 89 (63.1%) normal weight and 52 (36.9%) overweight/obese patients. Perianal disease and refractoriness to biologics were more frequent in overweight/obese than normal weight CD patients (9 [10.1%] vs 12 [23%], p=0.03; 0 [0%] vs 4 [23.4%], p=0.01). In UC group, there were 81 (56.6%) normal weight and 62 (63.4%) overweight or obese patients.

Conclusions: In IBD patients in follow up, the proportion of underweight patients is low. Overweight and obese CD patients showed a higher frequency of perianal disease and refractoriness to biologics. BMI may influence phenotype and responsiveness to biologics in CD.