Nutritional Rehabilitation and Medical Stabilization of Adolescents with Anorexia Nervosa: Length-of-Stay Predictors, Cardiovascular Recovery, Refeeding Safety, and Psychiatric Comorbidity Burden

Background/Objectives: Adolescents with anorexia nervosa (AN) face substantial medical and psychiatric risk during hospitalization. We examined predictors of length of stay (LOS), cardiovascular recovery, refeeding safety, and psychiatric comorbidity in a consecutive pediatric cohort at a national tertiary center. Methods: Retrospective cohort of 68 consecutively admitted adolescents (91.2% female; mean age 14.2 ± 1.8 years, range 8–17; 85.3% restricting type) admitted between January 2017 and May 2025. A structured nutritional rehabilitation protocol (1000–1200 kcal/day, escalating by 200 kcal/day every 48 h to 2500–3000 kcal/day) was implemented with daily serum electrolyte monitoring. Statistical analyses included paired tests, Spearman correlations, multivariable regression of log-transformed LOS, and partial correlations controlling for the admission BMI z-score. Results: Nutritional and cardiovascular parameters improved from admission to discharge. Mean supine heart rate (HR) increased by 28.4 bpm (95% CI 25.0–31.8; p < 0.001), and bradycardia prevalence (HR < 50 bpm) improved from 39.7% to 1.5%. Lower admission BMI z-score was associated with longer LOS; each 1-unit higher BMI z-score was associated with an 18.9% shorter LOS in adjusted log-LOS regression (p = 0.003). Exploratory analyses of HR recovery suggested that the magnitude of HR improvement was more closely associated with baseline BMI z-score and baseline supine HR than with caloric escalation. Systematic electrolyte monitoring documented no hypophosphatemia requiring intervention and no refeeding syndrome. Documented mental health comorbidities or clinically significant symptom clusters were present in 82.4% of patients. Conclusions: In this adolescent anorexia nervosa cohort, structured inpatient nutritional rehabilitation was associated with substantial cardiovascular and nutritional improvement. Baseline nutritional status was associated with hospital course and cardiovascular response, while LOS should be interpreted as a composite outcome influenced by nutritional severity, discharge criteria, mental health needs, and family readiness. The absence of refeeding complications is reassuring and suggests that the protocol was metabolically safe under systematic electrolyte monitoring in this specialized tertiary setting.