Risk factors for overweight among Brazilian adolescents of low-income families: a case-control study

Objective: To study risk factors for overweight among Brazilian adolescents of low-income families. Design: Case-control study of obese and non-obese adolescents. Setting: Anthropometric survey including 1420 students (aged 14-19 years) attending a public high school in Sao Paulo, Brazil. Methods: Selection of 83 overweight (body mass index (BMI) > 85th percentile) and 89 non-overweight (BMI > 5th percentile and < 85th percentile) subjects, frequency-matched by age, gender, pubertal development and socio-economic status. Among the nutritional, familial and behavioural data available, five covariates (parents' obesity, adolescents' past obesity, to have a best friend, dietary restriction and habit of napping) were included in the fitted hierarchical conditional logistic regression models. Measurements: Parents or guardians and adolescents were weighed, measured and answered a pre-tested questionnaire applied by trained nutritionists and paediatricians. Results: The prevalence of overweight was 15.2%. As previous risks, obese parents and obesity during infancy presented odds ratios (OR) and 95% confidence intervals (CI) of 2.23 (1.15-4.35) and 3.60 (1.47-8.80), respectively. As concurrent factors, the habit of napping, to have a best friend and reported dietary restriction presented OR (95% CI) of 3.43 (1-32-8-92), 5.15 (1-76-15-07) and 7.26 (2-95-17.88), respectively. Dietary patterns, frequency of obesogenic foods and other physical activity indicators presented no statistical significance. Conclusion: In case-control studies, OR may overestimate the true risks. Parents' obesity and previous childhood obesity were identified as risk factors; therefore these factors should be the target for preventive programmes and policies in order to prevent the burden of obesity in the near future.