Whole-body protein turnover and resting energy expenditure in obese, prepubertal obese children

Background: Obesity is becoming more frequent in Children; understanding the extent to which this condition affects not only carbohydrate and lipid metabolism but also protein metabolism is of paramount importance. Objective: We evaluated the kinetics of protein metabolism in obese, prepubertal children in the static phase of obesity. Design: In this cross-sectional study, 9 obese children (x̄ ± SE: 44 ± 4 kg, 30.9 ± 1.5% body fat) were compared with 8 lean (28 ± 2 kg, 16.8 ± 1.2% body fat), age-matched (8.5 ± 0.2 y) control children. Whole-body nitrogen flux, protein synthesis, and protein breakdown were calculated postprandially over 9 h from 15N abundance in urinary ammonia by using a single oral dose of [15N]glycine; resting energy expenditure (REE) was assessed by indirect calorimetry (canopy) and body composition by multiple skinfold-thickness measurements. Results: Absolute rates of protein synthesis and breakdown were significantly greater in obese children than in control children (x̄ ± SE: 208 ± 24 compared with 137 ± 14 g/d, P < 0.05, and 149 ± 20 compared with 89 ± 13 g/d, P < 0.05, respectively). When these variables were adjusted for fat- free mass by analysis of covariance, however, the differences between groups disappeared. There was a significant relation between protein synthesis and fat-free mass (r = 0.83, P <0.001) as well as between protein synthesis and REE (r = 0.79, P < 0.005). Conclusions: Obesity in prepubertal children is associated with an absolute increase in whole-body protein turnover that is consistent with an absolute increase in fat-free mass, both of which contribute to explaining the greater absolute REE in obese children than in control children.