It is essential to exclude previous respiratory conditions that may influence lung function and control variables that are indicatives of inflammation, including CRP, erythrocyte sedimentation rate, FeNO or serum levels of leptin, adiponectin, IL-6 and TNF-α, which will allow precise determination of the influence of overweight in lung function of children and adolescents with obesity. This evidence concerns the gene TNF and obesity due to melanocortin 4 receptor deficiency.