Associations of changes in BMI and body fat percentage with demographic and socioeconomic factors: the ELANA middle school cohort.

BACKGROUND AND OBJECTIVES

Adolescent weight and fat gain is determined by multiple factors. This study examined the association between changes in body fat indicators, excessive weight and fat gain, and sociodemographic factors among Brazilian adolescents over a 4-year period.

METHODS

Body mass index (BMI) and body fat percentage (BFP) of 809 middle school students (mean age: 11.8 ± 1.15 years) were evaluated annually, from 2010 to 2013. Linear mixed effects models were used to assess the trajectories of BMI and BFP in both boys and girls according to the type of school attended (public or private) and skin colour. General estimating equations logistic regression analyses were performed to investigate associations between sociodemographic variables and the development of overweight or high BFP.

RESULTS

Girls from private schools (p = 0.003) and white boys (p = 0.041) experienced bigger increases in BMI, as compared to girls from public schools and black/brown boys, respectively. White boys also had an increased chance of presenting excessive weight (OR = 3.28; CI 95%: 1.13-9.52) and BFP (OR = 3.32; CI 95%: 1.38-8.01) gain than black/brown boys. Conversely, white girls were less likely to present excessive body fat gain when compared to black/brown girls (OR = 0.42; CI 95%: 0.18-0.96).

CONCLUSIONS

Adolescents who experienced better socioeconomic conditions, especially boys, were more likely to have greater increases in body fat indicators. Our findings contribute to the better understanding of BMI trajectories and body composition changes during puberty, as well as demonstrates the relationship between socioeconomic variables and adiposity indicators among adolescents in middle-income countries.