Body Mass Index and Body Composition in Relation to Sexual Maturation

Abstract

To assess body mass index. (BMI) in relation to sexual maturation and verify how fat-free mass (FFM) and fat mass (FM) contribute to its increase. 1,275 White adolescents (656 girls and 619 boys), aged 9 to 18 years, were evaluated according to Tanner stages. FFM and FM were calculated by triceps and subscapular skinfold measurements and leg-to-leg bioelectrical impedance. BMI-for-maturation was distributed into percentiles. Fat-free mass index (FFMI) and body fat mass index (BFMI) were calculated based on BMI 50t" ph percentile values. During maturation, as BMI increases, girls gain FFMI (13.3 kg/m2 at B1 and 15.8 kg/m2 at B5) and BFMI (3.7 kg/m2 at B1 and 5.7 kg/m2 at B5)--proportionally more fat-- while boys gain FFMI (14.3 kg/m2 at G1 and 17.9 kg/m2 at G5) and lose BFMI (4.8 kg/m2 at G1 and 3.2 kg/m2 at G5). These data suggest that FFMI and BFMI-for-maturation should be assessed in adolescents monitored for overweight and obesity.