Hyperfiltration in Obesity: The Vicious Link Between Visceral Fat, Proteinuria, and Sodium Excretion

: Background/Objectives: The global rise in obesity represents a major public health issue, extending its detrimental impact beyond metabolic complications to encompass renal dysfunction. A key element in this relationship lies in the interaction between visceral obesity and glomerular hyperfiltration-an early, often silent indicator of kidney injury that may precede the onset of chronic kidney disease (CKD). Methods: In this monocentric, retrospective study, we evaluated 43 adults with obesity attending the Outpatient Clinic for Diet Therapy in Transplantation, Renal Failure and Chronic Pathology at the University of Naples Federico II between March 2022 and March 2024. Clinical, anthropometric, biochemical, and 24 h urinary parameters were recorded, along with several validated visceral adiposity indices. Glomerular hyperfiltration was assessed through measured creatinine clearance (mClCr) tertiles, while associations with adiposity indices, proteinuria, and urinary sodium excretion were explored. Results: Higher creatinine clearance values were significantly associated with increased levels of adiposity indices-particularly Lipid Accumulation Product (LAP), New Visceral Adiposity Index (NVAI), and Metabolic Score for Visceral Fat (METS-VF)-as well as greater proteinuria, urinary sodium excretion, and daily salt intake. Subjects with proteinuria ≥ 150 mg/day exhibited higher NVAI values and elevated sodium and potassium urinary excretion compared with those without proteinuria. Significant correlations emerged between LAP and mClCr, sodium excretion, and proteinuria, even after adjustment for age and BMI. Conclusions: Higher visceral adiposity indices were associated with increased creatinine clearance, proteinuria, and urinary sodium excretion in adults with obesity. These findings suggest that visceral adiposity may represent a useful marker of early obesity-related renal alterations. Prospective studies are warranted to determine the causal relationships and mechanisms underlying these associations.