title: Are the physically active adolescents belonging to the "at risk of overweight" BMI category really fat?
abstract: The adolescence is recognized as one of the critical periods for the development of obesity. Children and adolescents who practice sports regularly have higher muscle mass and lower percentage of body fat than their peers who are physically less active. Since body mass index (BMI) is a widely used indicator of overweight/obesity in spite of the fact that it directly measures excess in weight but not in fat, it often misclassifies athletic populations, both children and adults. The specific aim of this study was to evaluate whether BMI adequately assesses fatness in adolescents, especially physically active ones. The analysis was performed on anthropometric data from two surveys (1997 and 2009/2010) of Zagreb secondary school adolescents, 1315 girls and 1034 boys, aged 15-19 years. The group defined as "physically active" consisted of adolescents who practice organized sports (36.2% girls, 44.6% boys), while the "physically inactive" group was made of their peers who practice sport only as a part of physical education in schools. The standardized values, calculated within each sex by survey, were used for comparison of adolescents with different levels of physical activity. Physically active adolescents of both sexes had lower sum of skinfolds mean Z-valutes (Pgirls<0.05, Pboys<0.001); additionally, boys had higher Z-values for body weight (p<0.05) and triceps/subscaputar ratio (indicating peripheral distribution of body fat) (p<0.05) than their less active peers. In order to evaluate whether BMI was adequate indicator for body composition during adolescence, we estimated the concordance of above-median category defined by BMI and the other body fat indicators. The largest discrepancy was found for sum of skinfolds in both sexes and was more pronounced in physically active adolescents. This finding was further confirmed in more extreme BMI category (85th - 95th percentile) which indicated that adolescents categorized as "at risk of overweight" were predominantly characterized by larger lean body mass and not by increased fatness.
authors.affiliation: Institute for Anthropological Research, Zagreb, Croatia. matea@inantro.hr
authors.forename: Matea Zajc
authors.initials: MZ
authors.lastname: Petranović
authors.forename: Zeljka
authors.initials: Z
authors.lastname: Tomas
authors.forename: Tatjana
authors.initials: T
authors.lastname: Skarić-Jurić
authors.forename: Jasna
authors.initials: J
authors.lastname: Milicić
authors.forename: Nina Smolej
authors.initials: NS
authors.lastname: Narancić
mesh_terms: D000293:Adolescent; D015992:Body Mass Index; D017523:Croatia / Q000453:epidemiology; D005260:Female; D006306:Health Surveys; D006801:Humans; D008297:Male; D009043:Motor Activity / Q000502:physiology*; D050177:Overweight / Q000453:epidemiology* / Q000503:physiopathology*; D012307:Risk Factors; D012885:Skinfold Thickness; D055815:Young Adult