Inclusion Criteria:  Age 12-24 yrs Meets Diagnostic and Statistical Manual of Mental Disorders (DSM-5) criteria for AAN  Hospitalized with medical instability, as defined by:  night time heart rate (HR) <45 bpm, systolic blood pressure (SBP) <90 mmHg, temperature <35.6° C, orthostatic Δ HR >35 bpm, or orthostatic Δ SBP >20 mmHg  Exclusion Criteria:  Bulimia nervosa Current pregnancy Chronic disease (e.g. immune, renal disease) Acute/active suicidality or psychosis Hospital admissions for refeeding in the prior 6 mo.