BackgroundEating disorders together with the overweight and obesity are important health concerns in adolescents. ObjectiveTo analyse the individual and combined influence of overweight and physical fitness on the risk of developing eating disorders in Spanish adolescents. MethodsThe sample consisted of 3571 adolescents (1864 females), aged 13 to 18.5 years, from Spain who participated in the AVENA and AFINOS studies. The risk of eating disorders was evaluated using the SCOFF questionnaire. Body mass index was calculated and the adolescents were classified into two groups: overweight (including obesity) and non-overweight according to Cole’s cut-off points. Cardiorespiratory fitness in the AVENA Study was assessed by the 20-m shuttle-run test and the overall physical fitness level was self-reported in the AFINOS Study. ResultsOverweight adolescents had a higher risk of developing eating disorders than non-overweight adolescents (odds ratio [OR]=4.91, 95% confidence interval [CI]: 3.63-6.61 in the AVENA Study and OR=2.45, 95% CI: 1.83-3.22 in the AFINOS Study). Also, adolescents with medium and low levels of physical fitness had a higher risk of developing eating disorders (OR=1.51, 95% CI: 1.05-2.16, and OR=2.25, 95% CI: 1.60-3.19, respectively, in the AVENA Study, and OR=1.73, 95% CI: 1.37-2.17, and OR=4.11 95% CI: 2.98-5.65, respectively, in the AFINOS Study) than adolescents with high levels of physical fitness. In both studies, the combined influence of overweight and physical fitness showed that adolescents with lower levels of physical fitness had an increased risk of developing eating disorders in both non-overweight and overweight groups. ConclusionsPhysical fitness might attenuate the influence of overweight on the development of eating disorders in adolescents.