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.

Inflammatory bowel diseases (IBD), including Crohn's disease and ulcerative colitis, are associated with an increased risk of malnutrition and growth impairment in pediatric patients. Chronic inflammation, reduced oral intake, malabsorption, and increased metabolic demand may contribute to altered nutritional status and increased resting energy expenditure (REE).

Resting energy expenditure represents the amount of energy required to maintain basic physiological functions at rest and accounts for most daily energy consumption. Accurate evaluation of REE is important to optimize nutritional support and avoid underfeeding or overfeeding in children with IBD.

This study is a national multicenter prospective observational no-profit study involving pediatric patients aged 6 to 17 years with a new diagnosis of IBD according to ECCO/ESPGHAN criteria. Approximately 50 patients are expected to be enrolled.

REE will be measured using indirect calorimetry and compared with predictive equations. Clinical and laboratory parameters routinely collected during standard clinical care will also be evaluated, including disease activity indices (PUCAI/PCDAI), anthropometric measurements, biochemical parameters, fecal calprotectin, dietary intake, physical activity questionnaires, and endoscopic scores.

Data will be collected at diagnosis, after induction therapy, and during follow-up visits. The study aims to identify possible correlations between REE, disease activity, and dietary or pharmacological treatments in pediatric patients with IBD.

Inclusion Criteria:

• Pediatric patients aged 6 to 17 years
• New diagnosis of inflammatory bowel disease, including Crohn disease or ulcerative colitis, according to ECCO/ESPGHAN criteria
• Written informed consent signed by parents or legal guardians

Exclusion Criteria:

• Intestinal surgery within 6 weeks before the first evaluation
• Parenteral or enteral nutrition within 6 weeks before the first evaluation
• Eating disorders or other chronic diseases associated with possible malabsorption

Pediatric patients aged 6 to 17 years with newly diagnosed inflammatory bowel disease, including Crohn disease and ulcerative colitis, recruited from participating Italian centers with availability of indirect calorimetry assessment.