The fat mass and obesity-associated gene (FTO) has been extensively reported in the literature related to nutritional status, but there has been limited description of the genetic contribution to obesity risk during childhood and adolescence, especially in Latin Americans. This study aims to associate the rs9939609 polymorphism, of the FTO gene, with changes in nutritional status in Brazilian schoolchildren followed for 3 years. A longitudinal study was conducted with 355 schoolchildren, aged 7-15 years in 2011/2012 and subsequently re-evaluated in 2014/2015. Nutritional (obesity) status was classified by identifying those exceeding recommended thresholds for waist circumference (WC), waist-to-height ratio (WHtR), body mass index (BMI), and body fat percentage (BF%). The rs9939609 polymorphism was genotyped by a real-time polymerase chain reaction. Relative risk (RR with 95% confidence interval) of obesity status by FTO gene polymorphism was calculated by Poisson regression. The risk group was determined for genotypes with the allele A polymorphism, and regression models were adjusted for age, sex, height, ethnicity, and geographical location. Considering the longitudinal changes in status over the 3-year follow-up, the RR of developing a WC exceeding the threshold recommended (WC >75age and sex-standardized percentile), or remaining with this condition, was higher in children with AT/AA genotype. For WC, the RR was 1.66 (1.07; 2.58) in crude analysis and 1.17 (1.01; 1.35) following adjustment for age (years), gender, ethnicity, and geographical location. The comparative risk of abdominal obesity, assessed by WHtR (not recommended threshold ≥0.50), was 53% and 8%, respectively, higher in AT/AA compared to TT genotype.Conclusion: This is one of the first longitudinal investigations to show a significant association between the A allele of the rs9939609 polymorphism and individuals with higher than recommended WC and WHtR measures in Brazilian children and adolescents. What is known: • The FTO has an effect on increases in body mass index (BMI) among children and adolescents. • It established the association between FTO and overweight/obesity in Caucasians. What is new: • The presence of the risk allele of rs9939609 (FTO gene) polymorphism is associated with increased abdominal fat in Brazilian schoolchildren. • Was detected an association between FTO gene polymorphism (rs9939609) with WC in follow-up cohort and changes in WC and WHtR follow-up over 3 years, during childhood and adolescence growth. th
