BMI in the lower and upper quartiles at diagnosis and at 1-year follow-up is significantly associated with higher risk of disease exacerbation in pediatric inflammatory bowel disease.

Inflammatory bowel disease (IBD) has been associated with underweight and malnutrition, but obesity may also serve as a negative prognostic factor. This study aimed to present the longitudinal course of height, weight, and body mass index (BMI) of children from IBD diagnosis to 18 months of follow-up, and to describe the impact of BMI on the clinical course of the disease. One hundred and fifty-two children were identified, of whom 85 had Crohn's disease (CD) and 67 had ulcerative colitis (UC). During a median (interquartile range) follow-up of 2.95 (1.73-4.5) years, weight and BMI Z-scores increased in the first 18 months since diagnosis in both the CD (P < 0.001) and UC (P < 0.028) groups. BMI in lower and upper quartiles at diagnosis was associated with higher risk of hospitalization (hazard ratio [HR] = 2.72, P = 0.021). In a multivariate analysis, BMI in the lower quartile at diagnosis and at 6, 12, and 18 months was associated with higher risk of disease exacerbation (HR = 2.36, 1.90, 1.98, and 2.43, respectively, P < 0.021), as was BMI in the upper quartile (HR = 2.59, 2.91, and 2.29, respectively, P < 0.013).Conclusion: BMI in the lower and upper quartiles at diagnosis and during follow-up was associated with a more severe disease course in children with IBD. What is Known: • Inflammatory bowel disease (IBD) has been associated with underweight and malnutrition. • The impacts of weight and body mass index (BMI) on the presentation and course of IBD have been mainly investigated in the adult population. What is New: • In the era of the obesity epidemic, this study identifies both low and high BMIs at diagnosis and at follow-up as a marker for poor outcome in pediatric IBD. • The results support using BMI as a predictor of IBD course and prognosis.