Fat oxidation in nonobese and obese adolescents:: Effect of body composition and pubertal development

Objectives: To measure postabsorptive fat oxidation (F-ox and to assess its association with body composition (lean body mass [LBM] and body fat mass [BFM]) and pubertal development Design: We studied 235 control (male/female ratio = 116/119; age [mean +/- SD]: 13.1 +/- 1.7 ears; weight: 45.3 +/- 10.5 kg; LBM: 34.3 +/- 7.1 kg; BFM 11.0 +/- 4.5 kg) and 159 obese (male/female ratio 93/66; age: 12.9 +/- 2.1 years; weight: 76.2 +/- 19.1 kg; LBM: 47.4 +/- 10.9 leg; BFM: 28.8 +/- 9.2 kg) adolescents. Postabsorptive F-ox was calculated from oxygen consumption, carbon dioxide production, and urinary nitrogen as measured by indirect calorimetry and Kjeldahl's method, respectively Body composition was determined by anthropometry Results: Postabsorptive F-ox (absolute value and percentage of resting metabolic rate) uas significantly (p < 0.001) higher in the obese adolescents (76.7 +/- 26.3 gm/24 hours, 42.3% +/- 18.7%) than in the control subjects (40.0 +/- 26.3 gm/24 hours, 28.7% +/- 17.0%), even if adjusted for LBM. F-ox corrected for BFM was similar in control and in obese children, but was significantly lower in girls compared with boys (control mate subjects: 62.1 +/- 29.1 gm/24 hours, control female subjects: 51.6 +/- 28.4 gm/24 hours, obese male subjects: 57.3 +/- 29 gm/24 hour, obese female subjects: 45.0 +/- 28.4 gm/24 hours). BFM and LBM showed a significant positive correlation with F-ox. By stepwise regression analysis the most important determinant of F-ox vas BFM in obese and LBM in control children. There nias a significant rise in F-ox during puberty; however, it was mainly explained by changes In body composition Conclusions: Obese adolescents have higher Fox rates than their normal-weight counterparts. Both LBM and fat mass are important determinants of F-ox.