#1619 Protein intake and the risk of age-related kidney function decline in the general population—the Renal Iohexol Clearance Survey

Abstract Background and Aims In experimental studies, a high-protein diet (>1.3 g/kg/day) has been shown to cause hyperfiltration, which may lead to an accelerated decline in the glomerular filtration rate (GFR) with and without preexisting kidney disease. However, evidence is inconsistent regarding the impact of higher protein intake on GFR decline in individuals with normal kidney function. This inconsistency may stem from imprecise creatinine-based GFR estimates (eGFR), which can be biased by protein intake and muscle mass variations. We aim to use GFR measured as iohexol clearance (mGFR) to address the knowledge gap regarding protein intake and the risk of GFR decline. Method We analyzed data from the second Renal Iohexol Clearance Survey, RENIS, involving 1,066 participants without self-reported diabetes and cardiovascular disease, where mGFR was measured at baseline and after a median follow-up of 5.3 years. Protein intake (g/kg/d) was assessed using a validated food frequency questionnaire specifically designed to capture comprehensive dietary information based on Norwegian dietary habits and food items. We excluded participants with extreme total energy and/or protein intakes, defined as participants in the 1st and 100th percentiles of energy intake (<3417 kJ/d and >19666 kJ/d) and protein intake (<37.6 g/d and >200.9 g/d) to exclude unrealistic energy intakes (n = 35). We used linear mixed models and logistic regression to examine the association between estimated protein intake and the mean GFR decline rate and the odds ratio of accelerated GFR decline (top 10% steepest annual GFR reduction), adjusted for potential confounders. Results The mean baseline age of the participants was 63.7 years (52% women). The mean GFR was 88.8 ml/min/1.73 m2, and 4% had diabetes. The mean protein intake was 1.2 ± 0.4 g/kg/day. The lowest quartile of protein intake ranged from 0.4 to 0.9 g/kg/day, while the highest quartile ranged from 1.4 to 3.7 g/kg/day. Mean baseline mGFR was higher in groups with higher protein intake: 86.1, 88.5, 88.9, and 91.9 mL/min/1.73 m² from lowest to highest quartile, respectively. No association was found between estimated protein intake and mGFR decline, with a yearly change of −0.03 (95% CI: −0.08 to 0.02) per 0.1 g/kg/d increase. No differences were observed across protein intake quartiles. Increased protein intake was not associated with accelerated GFR decline. Results were consistent in sensitivity analyses using absolute GFR without body surface area adjustment. Conclusion The amount of protein consumed in the diet did not correlate with the rate of GFR decline in healthy individuals with normal kidney function. These findings suggest that restricting dietary protein intake does not prevent CKD.