Patients with restrictive-type anorexia nervosa who are admitted to the hospital for feeding often urinate excessive amounts. Others have changes in the way that they handle acid and base. These issues prolong hospitalizations. Current data suggest that one hormone--named secretin--may control both urine output and how the body handles acid and base. This study will evaluate whether secretin levels are different in anorexic patients who urinate an excessive amount compared to those who urinate normal amounts. For this study, patients will have one extra blood draw before and after one meal during their hospitalization. The blood draw before the meal coincides with a standard of care blood draw. Also after the meal, subjects will be asked to provide one extra urine sample. Information from subject's medical records will also be used.