BackgroundWe intended to evaluate the effects of physical activity (PA) programs on renal function in obese boys.MethodsThirty-nine boys participated in one of the following three groups: soccer (SG, n=13), traditional PA (AG, n=13), and sedentary control (CG, n=13). SG and AG were involved in 6-month PA programs, involving three sessions/week for 60-90 min. Anthropometric measurements, body composition, creatinine and cystatin C plasmatic levels, and estimated glomerular filtration rate (eGFR) were evaluated.ResultsAt baseline (n=39), age and lean mass index (LMI) were positively correlated with creatinine levels. After 6 months, both intervention groups decreased the BMI z-score and waist circumference, while the CG increased the body fat percentage (BFP). LMI increased in all the groups. SG presented a small increment in plasma creatinine and a decrease in the eGFR values, using the Schwartz formula. Concerning the cystatin C levels and eGFR values using Filler (cystatin C-based) or Combined Zappitelli (creatinine/cystatin C-based) formulas, no significant changes were observed in any group.ConclusionThe combined Zappitelli formula showed no significant impact of PA on eGFR in obese boys. Although plasma creatinine is significantly influenced by lean body mass, cystatin C is likely to be a more accurate marker of renal function in this population.