Background: Growth impairment is commonly seen in children diagnosed with inflammatory bowel diseases (IBD), mainly those with Crohn's disease (CD). There is general consensus in the literature that body composition, composed of fat mass and lean mass is altered in children with IBD compared with controls. Evidence regarding the effect of different therapeutic approaches on body composition in children with IBD is scarce and inconsistent. Furthermore, most studies used anthropometric measures and dual energy X-ray absorptiometry (DEXA) for body composition assessment, while information on the usefulness of air displacement plethysmography (ADP) for this assessment is lacking.

Objectives: To assess body composition in children with IBD by ADP and DEXA at diagnosis and at various intervals during follow up.

Design: A prospective cohort study. Setting: Pediatric gastroenterology institute, Schneider Children's Hospital.

Participants: Children 6 year to 17 years who are diagnosed with either CD or ulcerative colitis (UC).

Main outcome measures: Accuracy of ADP in comparison to DEXA and percentage of fat mass and lean mass at diagnosis and during treatment.

Secondary outcome measures: Correlation of body composition to skin fold, mid arm circumference measurements, BMI, inflammatory markers, gender, disease activity and physical activity.

Children diagnosed with either Crohn's disease (CD) or Ulcerative Colitis (UC) under follow-up at the Pediatric gastroenterology institute, Schneider Children's Hospital, will be enrolled. Patients can be enrolled at diagnosis or at any time point during follow-up. Patients' characteristics will be retrieved from their medical files including demographic details, disease phenotype, anthropometric measures, laboratory evaluation, complication and therapeutic regimens. At enrollment all patients will perform body composition assessment by air displacement plethysmography (ADP) and DEXA (no greater than 7 days between the 2 methods of measurement). At one and two years following initial assessment ADP measurement will be repeated, mid arm circumference and skin fold measurements will be taken and the patient will fill a physical activity questionnaire. Disease activity score (either Pediatric Crohn's Disease Activity Index for CD or Pediatric Ulcerative Colitis Activity Index for UC) will be calculated. Similar evaluation will be performed prior and immediately following exclusive enteral nutrition or corticosteroid courses and prior to any biologic therapy initiation.

Inclusion Criteria:

• Diagnosis of IBD
• Age: 6 - 17 years ( inclusive)
• Informed consent

Exclusion Criteria:

• Pregnancy
• Non IBD associated chronic diseases
• Morbid obesity

Children at age 6 year to 17 years diagnosed with IBD