Protein and Energy Metabolism in Pediatric Crohn's Disease

Inclusion Criteria: * Male and female children between the ages of six and eighteen years of age with recurrence of active Crohn's disease, determined by their primary pediatric gastroenterologist to require either: 1. Corticosteroid therapy ((1-2 mg/kg/d up to maximum of 60 mg/day) with taper, or 2. Infliximab therapy (5 mg/kg at 0, 2, and 6 weeks, followed by q 8 week therapy) * Crohn's disease of at least 3 months since diagnosis, with gastritis, duodenitis, ileitis, ileocolitis, or colitis, confirmed by endoscopy and biopsy * PCDAI score \>20 * If receiving concomitant medications, must have been on a stable regimen as follows: 1. Subjects on aminosalicylates and/or immunomodulators should be on a stable dose for at least 2 weeks prior to enrollment. 2. Subjects must be off oral, rectal, and parenteral corticosteroids at least 2 weeks prior to enrollment. * Screening laboratory tests that meet the following criteria (obtained within 4 weeks of enrollment): 1. Hemoglobin \>8.0 g/dL 2. White blood cell count \>3.5 x 109/L 3. Neutrophils \>1.5 x 109/L 4. Platelets \>100 x 109/L 5. Aspartate aminotransferase, alanine aminotransferase, and alkaline phosphatase levels within 3 times the upper limit of normal. * For those patients to receive infliximab, PPD skin tests with skin induration \<5 mm. * Signed written consent from the parent/legal guardian and assent from the child to be obtained prior to enrollment. Exclusion Criteria: * Local manifestations of Crohn's disease, including fistula(s), strictures, abscesses, or other complications for which surgery may be indicated. * Surgery for bowel diversion with placement of stoma within 3 months prior to screening. * Positive stool examination of enteric pathogens including Salmonella and Shigella species, Clostridium difficile, and Giardia lamblia. * Female subjects who are pregnant, nursing, or planning pregnancy. * Concomitant diagnosis or history of congestive heart failure. * Treatment with parenteral nutrition within 4 weeks of enrollment. * Serious infection in the 3 months prior to enrollment. * History of prior or current active or latent tuberculosis. * Immune deficiency syndrome, including documented human immunodeficiency virus (HIV) or acquired immunodeficiency syndrome (AIDS). * History of systemic lupus erythematosus. * A transplanted organ. * Known malignancy or history of malignancy within 5 years of enrollment. * History of demyelinating disease. * History of substance abuse. * Poor tolerability of venipuncture or lack of venous access during the study period. * A live virus vaccination within 3 months of enrollment. * Prior history of infliximab infusion, or any other therapeutic agent targeted at reducing tumor necrosis factor-a (TNF-a). * Hypersensitivity to any murine proteins or other component of infliximab for those patients to receive infliximab. * Inability to comply with study procedures