Associations between physical fitness and adherence to the Mediterranean diet with health-related quality of life in adolescents: results from the LabMed Physical Activity Study

Background: Physical fitness (PF) and adherence to the Mediterranean diet are important indicators of healthy lifestyles. The purpose of this study is to analyze the independent and combined associations between PF and adherence to Mediterranean diet with health-related quality of life (HRQoL) in adolescents. Methods: This is a cross-sectional analysis with 956 Portuguese adolescents aged 12-18 years. HRQoL was measured with the Kidscreen-10 questionnaire. PF was assessed with the ALPHA health-related fitness battery. The 20-m shuttle run test was used for the estimation of cardiorespiratory fitness; handgrip strength and standing long jump tests were applied for the assessment of muscular fitness and the 4 10 m shuttle run test for the assessment of motor fitness (speed and agility). The results of the PF tests (cardiorespiratory fitness, muscular fitness and motor fitness) were transformed into standardized values (Z-scores) by age and sex. Adherence to the Mediterranean diet was assessed with the KIDMED index. Regression analysis and analysis of covariance were performed. Results: PF (B = 0.228; P < 0.05) and adherence to the Mediterranean diet (B = 0.259; P < 0.05) were positively associated with HRQoL, after controlling for several variables. Participants classified as high PF and high adherence to Mediterranean diet had on average the highest HRQoL score compared with those with low PF and low adherence to Mediterranean diet (F(3, 939) = 4.270; P = 0.005), after adjustments for potential confounders. Conclusions: The combination of high PF levels and optimal adherence to Mediterranean diet is positively associated with HRQoL.