Modeling the dynamics of BMI changes during adolescence. The Oporto Growth, Health and Performance Study

The aims of this study were twofold: (i) to model changes in body mass index (BMI) of 10-18-year-old adolescents, and (ii) to investigate the effects of total physical activity (TPA), physical fitness (PF), sleep duration and fruit/vegetable consumption in BMI trajectories across time.

Data were obtained from the Oporto Growth, Health and Performance Study and comprised 6894 adolescents (3418 girls) divided into four age cohorts (10, 12, 14 and 16 years) measured annually for 3 years. BMI was computed using the standard formula (kg m(-2)); TPA was estimated with the Baecke questionnaire; PF measures included 1-mile run/walk, 50 yard dash (50YD), standing long jump (SLJ), handgrip strength (HGr) and agility shuttle run. Longitudinal changes in BMI were analyzed using the multilevel modeling approach.

The average BMI at age of peak of height velocity was 20.7±0.07 kg m(-2) for girls (P<0.001) and 20.58±0.06 kg m(-2) for boys (P<0.001). The annual increment in BMI was 1.36±0.04 kg m(-2), P<0.001 and 1.23±0.03 kg m(-2), P<0.001 for girls and boys, respectively. PF were related to BMI trajectories in both sexes (Girls: β1mile=0.12±0.02, P<0.001; βSLJ=-0.01±0.00, P<0.001; β50YD=0.28±0.05, P<0.001; βHGr=-8.91±0.54, P<0.001; Boys: β1mile=0.18±0.02, P<0.001; βSLJ=-0.01±0.00, P<0.001; β50YD=0.26±0.04, P<0.001; and βHGr=-8.15±0.45, P<0.001). TPA only showed significant, but positive, association with girls' BMI trajectories (β=0.10±0.03, P=0.001). After adjusting for the covariates, sleep duration and fruit/vegetable intake did not show any significant association with BMI trajectories either sex.

BMI increased linearly with age in both gender. PF levels are negatively associated with BMI across time in both boys and girls. Therefore, promotion of PF in the adolescent years seems to be effective in the early prevention of obesity.