Higher habitual protein intake is not linked to decline of iohexol-measured GFR in adults ≥40 years.

BACKGROUND

High habitual dietary protein intake may increase glomerular workload and contribute to hyperfiltration, but the long-term renal effects in individuals without chronic kidney disease remain debated. Prior population studies have relied on estimated glomerular filtration rate, which may be biased by non-GFR determinants. We examined whether higher protein intake is associated with decline in kidney function using repeated measurements of iohexol-measured GFR (mGFR).

METHODS

We analysed data from the Renal Iohexol Clearance Survey, a population-based cohort with repeated mGFR measurements over follow-up (n = 1324). Baseline protein intake was estimated using a validated food-frequency questionnaire. Associations of protein intake with GFR decline rate, accelerated GFR decline (top 10% with the steepest annual reductions), and incident mGFR <60 ml/min/1.73 m² were assessed using linear mixed models, logistic regression, and interval-censored Cox regression.

RESULTS

Mean age was 64 years, 50% were women, and mean baseline mGFR was 89 ml/min/1.73 m². Median follow-up was 10 years. Mean reported protein intake was 1.2 ± 0.5 g/kg/day, with the lowest quartile consuming <0.9 g/kg/day and the highest ≥1.4 g/kg/day. Protein intake was not associated with mGFR decline [-0.01 ml/min/1.73 m² per year (95% CI -0.04 to 0.02) per 0.1 g/kg/day higher protein intake]. Protein intake was not associated with accelerated GFR decline or incident mGFR <60 ml/min/1.73 m².

CONCLUSIONS

Among middle-aged and older adults in the general population, higher estimated habitual protein intake was not associated with mGFR decline.