Changes in eGFR in adolescent and young adult inpatients receiving nutritional rehabilitation for a restrictive eating disorder: a five-year clinical audit

Background: Impaired renal function may be observed in individuals with a restrictive eating disorder, yet its prevalence and underlying pathophysiological mechanisms are inadequately characterised. The impact of elevated protein intake on estimated glomerular filtration rate (eGFR) in this demographic remains unclear, leading to a lack of specific guidelines regarding protein prescriptions during inpatient treatment. This study describes changes in eGFR as a marker of renal function among adolescents and young adults receiving inpatient care for restrictive eating disorders and evaluates protein prescriptions during nutritional rehabilitation. Methods: A retrospective audit of adolescent and young adults hospitalised with restrictive eating disorders (2016–2020) on a specialised medical ward was conducted. Data collected included anthropometric measurements, age, serum creatinine, blood urea, energy and protein prescriptions, medical stability upon admission, and hospital length-of-stay. The eGFR was calculated using the CKiDU25 equation. A random intercepts model was employed to assess the relationship between protein intake and eGFR changes during hospitalisation, controlling for confounding variables including age, sex, %mBMI, medical instability, and purging history. Results: Among the 187 admissions that met inclusion criteria, the mean age was 17.0 ± 1.2 years, 90.9% (n = 170) were females, and mean %mBMI was 80.1 ± 9.5% at admission. Impaired renal function (eGFR < 90 mL/min/1.73 m²) was observed in 35.3% of patients at admission, and 3.2% of patients at discharge. Protein intake increased from 1.9 ± 0.4 g/kg/day on admission to 2.7 ± 0.6 g/kg/day at discharge. Conclusions: Impaired renal function was observed in approximately one third of this sample of adolescents and young adults hospitalised with restrictive eating disorders and typically resolves during the admission. A high protein prescription of 1.9–2.7 g/kg/day did not deleteriously affect renal function, with eGFR levels improving with nutritional rehabilitation. Prospective studies are needed to confirm the optimal protein prescription during nutritional rehabilitation in patients hospitalised with restrictive eating disorders, and to further explore outcomes in the small subgroup of patients who remain with renal impairment at discharge.