The investigators will prospectively recruit 26 children with moderate - severe active Crohn disease (PCDAI >30). Results will be compared to 26 patients in sustained remission (PCDAI <10 and physician global assessment of remission over the previous 6 months) who are matched for age and gender. Subjects will be studied at baseline and six months. The primary study end-points will be leucine rate of appearance (a measure of protein breakdown) and IGF-1 levels.