A weight reduction program preserves fat-free mass but not metabolic rate in obese adolescents

OBJECTIVE: To determine the effects of a multidisciplinary weight reduction program on body composition and energy expenditure (EE) in severely obese adolescents. RESEARCH METHODS AND PROCEDURES: Twenty-six severely obese adolescents, 12 to 16 years old [mean BMI: 33.9 kg/m(2); 41.5% fat mass (FM)] followed a 9-month weight reduction program including moderate energy restriction and progressive endurance and resistance training. Body composition was assessed by DXA, basal metabolic rate by indirect calorimetry, and EE by whole-body indirect calorimetry with the same activity program over 36-hour periods before starting and 9 months after the weight reduction period. RESULTS: Adolescents gained (least-square mean +/- SE) 2.9 +/- 0.2 cm in height, lost 16.9 +/- 1.3 kg body weight (BW), 15.2 +/- 0.9 kg FM, and 1.8 +/- 0.5 kg fat-free mass (FFM) (p < 0.001). Basal metabolic rate, sleeping, sedentary, and daily EE were 8% to 14% lower 9 months after starting (p < 0.001) and still 6% to 12% lower after adjustment for FFM (p < 0.05). Energy cost of walking decreased by 22% (p < 0.001). The reduction in heart rate during sleep and sedentary activities (-10 to -13 beats/min), and walking (-20 to -25 beats/min) (p < 0.001) resulted from both the decrease in BW and physical training. DISCUSSION: A weight reduction program combining moderate energy restriction and physical training in severely obese adolescents resulted in great BW and FM losses and improvement of cardiovascular fitness but did not prevent the decline in EE even after adjustment for FFM.