Patients will be asked to not eat or drink anything for 8 hours before the second visit, and will be asked to bring a bathing suit and a swim cap to the Clinical Center. On the day of the visit, patients will fill out questionnaires to provide information about symptoms, current levels of gastrointestinal pain, and general quality of life. Patients will also provide a blood sample for testing. Researchers will measure patients blood pressure and heart rate, height, weight, waist/hip circumference, and intra-abdominal measurement. Patients will also be asked to put on the bathing suit and swim cap to have their body fat measured using a machine called the BOD POD. To test the gastrointestinal system, patients will then be asked to drink a sugar-based test solution, and researchers will collect all voided urine for the next 5 to 6 hours. (Patients may drink water during this time.)