Mediation of obesity-related variables in the association between physical fitness and cardiometabolic risk in children and adolescents: a systematic review and meta-analysis

Objective. To examine the mediation of obesity-related variables in the association between physical fitness and cardiometabolic risk in children and adolescents. Design. Systematic review and meta-analysis. Data sources. Studies from electronic databases from inception to 31 December 2023. Eligibility criteria for selecting studies. Included were 123 observational studies (cross-sectional and longitudinal) that assessed risk by constructing a continuous score incorporating cardiometabolic parameters. Studies were considered if they evaluated at least one fitness component as an exposure in children and adolescents (5–19 years). Thirty-one were included in the main meta-analyses. Results. Cross-sectional findings indicate that cardiorespiratory fitness is modestly but beneficially associated with cardiometabolic risk, either indirectly via obesity-related variables (indirect standardized beta coefficient [βIndirect]=−0.17; 95% confidence interval [CI] −0.23; −0.11; inconsistency index [I2]=94.4%) or directly and independently from obesity-related variables (r=−0.11; 95% CI −0.15; −0.07; I2=87.4%), whereas muscular fitness seems to be associated with risk only via obesity-related variables (βIndirect=−0.34; 95% CI −0.47; −0.20; I2=85.1%). There was no cross-sectional difference between biological sexes (p≥0.199). Longitudinal findings indicate no total (r=−0.12; 95% CI −0.24; 0.01; I2=23.1%) and direct (r=−0.03; 95% CI −0.08; 0.03; I2=0%) associations. Conclusion. The association between fitness and risk appears to take place either indirectly through the reduction of obesity-related levels or directly by influencing risk. The latter underscores that the inverse association extends beyond a mere reduction in obesity-related variables, encompassing specific enhancements linked to exercise training, including increased metabolic efficiency, and cardiovascular capacity. PROSPERO registration number. CRD42022354628.