Lean mass modulates glomerular filtration rate in males of normal and extreme body composition

Background: Understanding determinants of glomerular filtration rate (GFR) is important in aiding prediction and interpretation of kidney function. Body composition is known to affect GFR but is not included in current screening of kidney disease. We investigated the association between GFR and body composition in healthy young men with differing body mass but without known diabetes or kidney injury. Methods: Three groups were recruited: normal BMI (n = 22) with a body mass index (BMI) <25 kg/m 2 , muscular (n = 23) with BMI ≥30 kg/m 2 and bioelectrical impedance body fat ≤20% and obese (n = 22) with BMI ≥30 kg/m 2 and bioelectrical impedance body fat ≥30%. Dietary analyses, GFR clearance by 99m Tc-DTPA, urine protein and body composition by dual-energy X-ray absorptiometry were measured in all participants. Linear and nonlinear associations of constituents of body composition with GFR were assessed. Results: Muscular men had a higher GFR (mean 186.4 mL/min; 95% CI 171.7‐201.1) than normal BMI and obese groups (P = 0.0007). Urine protein and albumin excretion were not elevated in any participants. On multiple regression analysis (r 2 = 0.60), the variables with strong associations with GFR were age (P = 0.0009) and lean mass (P = 0.0001). Fat mass, protein intake and smoking status were not associated. Skeletal muscle mass correlated significantly with GFR in all subgroups. Conclusion: Age and lean mass were strong determinants of GFR. Estimates of GFR should therefore be indexed to an estimate of lean mass.