 - Patients evaluated in the CAIR Program at Boston Childrens Hospital will be eligible for participation if they meet the definition of short bowel syndrome and are under 18 years of age. Short bowel syndrome will be defined as a malabsorptive state resulting from congenital or acquired gastrointestinal disease leading to current dependence on parenteral nutrition for greater than or equal to 90 days. If the patient is on intravenous fluids, they must have a stable intravenous fluid regimen for at least 4 weeks prior to the study visit. 