Basal metabolic rate in anorexia nervosa: relation to body composition andleptin concentrations

Background: Leptin is thought to represent a peripheral signal involved in the regulation of energy balance. Its action has been studied in animals an d obese subjects. Little is known about leptin's role during negative energ y balance. Objective: The objective was to evaluate the relation between energy turnov er, body composition, and plasma leptin concentrations in anorexia nervosa (AN). Design: Sixteen weight-stable women with AN were compared with 22 control s ubjects and 14 rehabilitated AN patients (R-AN). Basal metabolic rate (BMR) was measured by indirect calorimetry; fat-free mass (FFM) and fat mass (FM ) were calculated according to a 4-compartment model. Plasma leptin was det ermined by radioimmunoassay. Results: The BMR of AN patients (2.73 +/- 0.37 kJ/min) was significantly lo wer than that of control subjects (3.45 +/- 0.34 kJ/min) (P < 0.001), even after adjustment for FFM (2.92 +/- 0.33 kJ/min in AN patients and 3.30 +/- 0.26 kJ/min in control subjects; P < 0.004). Plasma leptin concentrations i n AN patients were 76% lower than in control subjects, even after body fat was controlled for. In R-AN patients, BMR was not significantly different f rom that of control subjects and leptin concentrations were generally close to normal. Plasma leptin concentrations correlated significantly with FM ( r(2) = 0.53, P < 0.0000) and BMR, even after adjustment for FFM (r(2) = 0.2 1, P < 0.0003). Conclusions: BMR and plasma leptin concentrations are depressed in patients with AN; this is not explained by body-composition changes. The relation b etween leptin and BMR suggests that leptin plays a role in the energy spari ng response to exposure to chronic energy deficiency. The return of BMR to normal and the significant increase in leptin concentrations in R-AN patien ts suggests a full reversibility of this adaptation mechanism.