This multicenter prospective observational non-pharmacological study aims to evaluate resting energy expenditure (REE) in pediatric patients affected by inflammatory bowel disease (IBD), including Crohn's disease and ulcerative colitis. REE will be measured using indirect calorimetry and estimated using predictive equations. The study also aims to investigate the relationship between REE, disease activity, and dietary or pharmacological treatments. Clinical, laboratory, anthropometric, nutritional, and disease activity data will be collected during routine clinical follow-up at diagnosis, after induction therapy, and during follow-up visits.