Abstract 166

Aim: To test the hypothesis whether energy expenditure (EE) of the metabolic active tissue (i.e. lean body mass, LBM) is influenced by the degree of obesity (more fat mass / more leptin / more EE).

Methods: 33 in-patients (13 girls, 20 boys; age 11.8 ± 3.7 yrs). Evaluation of resting EE (REE) and body composition (LBM, %body fat (%BF)) routinely obtained for diagnosis of obesity of otherwise healthy children or before starting long-term inhaled steroids for chronic bronchitis. REE: indirect calorimetry, thermoneutral conditions; 30 min of rest followed by a sampling interval of 30 min (Deltatrac II, Datex); body composition: Dual-energy x-ray absorptiometry (QDR-1500, Hologic), adult whole body software.

Results: (Mean ± SD) body weight (BW): 59.5 ± 19.8 kg; length: 157.3 ± 12.9 cm; BMI: 23.8 ± 6.1 kg/m2, %BF: 34.6 ± 13.1%; REE: 1710 ± 390 kcal/d. REE/BW: 30.0 ± 5.2, REE/LBM: 48.6 ± 6.8 kcal/kg/d. REE as related to LBM increases with increasing %BF (r = 0.536, p < 0.01). Subjects with %BF between 40 - 55% consumed 53. ± 5 compared to 43 ± 4 kcal/kgLBM/d in subjects with %BF between 10 - 25% (significant difference, p < 0.001).

Discussion: The data suggest that the level of energy turnover in the metabolic active tissue is directly related to the degree of obesity. It is unclear whether the elevated metabolic activity in obese subjects is caused by induction via the leptin loop or because components of REE (e.g. breathing) work less economically (more weight per lean mass to move).