Time course and determinants of leptin decline during weight loss in obese boys and girls

Objective. To investigate whether changes in leptin concentrations during weight loss can be explained by gender, puberty, baseline adiposity and changes in adiposity, body composition, rate of weight loss, physical activity and insulin concentrations. Design. A longitudinal study with 9 repeated measures during a 12-week weight loss programme. Subjects. Fifty-three boys and 62 girls (7.9-15.2 years) with body mass index (BMI) standard deviation scores (SDS) of median 2.78 and 2.70, respectively. Measurements. Height, weight, fat mass percentage assessed by bioimpedance, Tanner stages, testicular size, physical activity scores, blood leptin (ng/ml) and insulin concentrations (pmol/l) were measured at baseline, and except for Tanner stage and testicular size, repeated regularly during the programme. Results. The weight loss was accompanied by a steep decline in leptin concentrations during the first 10-11 days, followed by a less steep decline until day 82. Leptin declined to 39% in boys and 51% in girls of the level that was expected given the relationship at baseline between leptin and BMI SDS, and the BMI SDS changes during weight loss. The biphasic leptin decline was independent of gender, puberty, baseline adiposity or concomitant changes in BMI SDS, fat mass percentage, rate of weight loss, physical activity scores or insulin concentrations. Conclusion. The biphasic leptin decline, which exceeded the level expected, was independent of puberty, baseline adiposity and changes in adiposity, body composition, rate of weight loss, physical activity scores and insulin concentrations. The dissociation of the leptin-weight relationship during weight loss may contribute to the general leptin variability in obese subjects.