Variations and determinants of energy expenditure as measured by whole-body indirect calorimetry during puberty and adolescence.

BACKGROUND

Adolescence is characterized by rapid anatomic, physiologic, and behavioral alterations expected to induce changes in metabolic rate.

OBJECTIVE

The aim of the present study was to investigate variations in daily energy expenditure (DEE) and its main components during adolescence and to quantify their significant determinants.

DESIGN

Eighty-three children and adolescents (44 boys and 39 girls aged 10-16 y) participated in this cross-sectional study. Tanner stages ranged from 1 to 5. Body composition was assessed by both the skinfold-thickness method and bioimpedance analysis. Energy expenditure (EE) was determined continuously over 24 h by using 2 whole-body calorimeters. The subjects followed a standardized activity program that included four 15-min periods of exercise on a cycle ergometer.

RESULTS

Body composition, DEE, sleeping EE (SEE), resting EE, and EE during meals, miscellaneous activities, and physical exercise varied significantly with sex and stage of puberty. The DEE of boys and girls averaged 8.22 and 7.60 MJ in prepubertal children, 11.35 and 9.10 MJ in pubertal children, and 11.73 and 9.68 MJ in postpubertal adolescents, respectively. The significant determinants of DEE and SEE, respectively, were fat-free mass (r2 = 0.842 and 0.826), sex (r2 = 0.017 and 0.022), and season (r2 = 0.021 and 0.011). Stage of puberty and fat mass were not significant factors. DEE and SEE adjusted for fat-free mass were on average 5% higher in boys than in girls and 6% higher in spring than in autumn.

CONCLUSIONS

The DEE of adolescents measured under standardized conditions varied with sex, body composition, and season, but not with stage of puberty. These variables could be predicted accurately from fat-free mass, sex, and season.