Abstract
OBJECTIVE: To assess the genetic contribution to determinants of therapeutic weight loss in obese female identical twins. DESIGN: Subjects were studied for 40 days on an inpatient unit in three phases: 7 baseline days; 28 days of weight reduction by a very low calorie diet (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 rate by indirect calorimetry were assessed before and after weight loss.
RESULTS: There was great variability among pairs in loss of weight (5.9 - 12.4 kg) and body fat (3.1 - 12.4 kg). By contrast, the intraclass correlation (ICC) within twin pairs was 0.85, P < 0.001 for weight and 0.88, P < 0.001 for body fat.
A measure of metabolic efficiency, calculated as the difference between 'estimated' and 'measured' energy deficit showed high intrapair 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 contribution.