This study aims to describe associations of obesity and CKD in a Swedish urban population. The impact of fat mass, from bioimpedance analysis, on eGFR based on cystatin C and/or creatinine is studied. 5049 participants from Malmö Diet and Cancer Study the cardiovascular arm (MDCS-CV) with available body mass composition (single frequency bioimpedance analysis) and cystatin C measured at baseline were selected. Body mass index (kg/m.sup.2) was used to define overweight/obesity. eGFR was calculated using cystatin C (eGFR.sub.CYS) and creatinine (eGFR.sub.CR) equations: Chronic Kidney Disease Epidemiology Collaboration 2012 (CKD-EPI.sub.CR, CKD-EPI.sub.CYS, CKD-EPI.sub.CR-CYS).sub., eGFR.sub.CYS based on Caucasian, Asian, pediatric, and adult cohorts (CAPA), the Lund-Malmö revised equation (LMrev), and Modified Full Age Spectrum creatinine-based equation (EKFC.sub.CR). Two different fat mass index (FMI) z-scores were calculated: FMI z-score.sub.Larsson and FMI z-score.sub.Lee. Lower eGFR.sub.CYS and eGFR.sub.CR-CYS following multiple adjustments were prevalent in overweight/obese subjects. Increase in FMI z-score.sub.Larsson or FMI z-score.sub.Lee was related to decrease in predicted CAPA, CKD-EPI.sub.CYS, CKD-EPI.sub.CR-CYS and CAPA-LMrev equation. eGFR.sub.CYS, in contrast to combined eGFR.sub.CR-CYS and eGFR.sub.CR, demonstrate the strongest association between FMI and kidney function.