Serum Leptin and Thyroid Levels in Hospitalized Patients With Severe Eating Disorders

Leptin and thyroid hormones are interrelated regulators of energy homeostasis that are altered during starvation, yet their within-subject trajectories during early nutritional rehabilitation in severe restrictive eating disorders (EDs) remain poorly understood. This study examined how leptin and thyroid hormones change with initial weight gain in severely malnourished inpatients with an ED.

Data from 62 adult inpatients admitted to a specialized medical unit were analyzed. Blood samples measuring leptin, triiodothyronine (T3), thyroxine (T4), and reverse T3 (RT3) were obtained at admission, each 1.5 kg/m² increase in BMI, and discharge. Receiver operating characteristic (ROC) curves identified optimal BMI thresholds for clinically abnormal hormone levels, and multilevel models examined hormonal trajectories over BMI change.

At admission, leptin was undetectable in 74.2% of patients, T3 was low in 96.8% of patients, T4 was normal in all patients, and RT3 was low-to-normal in most patients. By discharge, most patients still remained underweight. Leptin remained undetectable in 24.2% of patients, and T3 normalized in only 22.6%. No BMI thresholds were clinically significant for identifying abnormal lab levels. Leptin increased linearly with BMI gain, while thyroid hormones demonstrated a biphasic pattern: T3 rose exponentially before plateauing, while T4 and RT3 declined sharply before rebounding, all around +2.0 kg/m².

T4 and RT3 did not demonstrate expected trajectories for severe malnutrition, while T3 and leptin trajectories were proportional to weight gain but incomplete. Additional follow-up through complete weight restoration is needed to fully understand the interrelation of these hormones, and how and when they normalize.