A twin study of weight loss and metabolic efficiency

OBJECTIVE: To assess the genetic contribution to determinants of therapeuti c weight loss in obese female identical twins. DESIGN: Subjects were studied for 40 days on an inpatient unit in three pha ses: 7 baseline days; 28 days of weight reduction by a very low calorie die t (1.6 MJ per day); and 5 days after weight reduction. SUBJECTS: Fourteen pairs of premenopausal obese female identical twins (age : 39.0 +/- 1.7 y; body weight (BW): 93.9 +/- 21.2 kg; body mass index (BMI) : 34.2 +/- 7.8 kg/m(2)). MEASUREMENTS: Body composition by hydrodensitometry and resting metabolic r ate by indirect calorimetry were assessed before and after weight loss. RESULTS: There was great variability among pairs in loss of weight (5.9 - 1 2.4 kg) and body fat (3.1 - 12.4 kg). By contrast, the intraclass correlati on (ICC) within twin pairs was 0.85, P < 0.001 for weight and 0.88, P < 0.0 01 for body fat. A measure of metabolic efficiency, calculated as the diffe rence between 'estimated' and 'measured' energy deficit showed high intrapa ir correlation (ICC = 0.77; P < 0.001). CONCLUSIONS: The high correlation in metabolic efficiency within twin pairs in response to therapeutic weight loss suggests a strong genetic contribut ion.