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Introduction: Epidemiologic studies have demonstrated that high dietary protein intake may increase risk of nephrolithiasis. The current study examines the relationship between dietary protein intake and 24-hour urine composition in patients with nephrolithiasis.
Materials & Methods:
A retrospective review was performed. Multivariate linear regression examined the relationship between protein intake and 24-hour urine composition. Regression models adjusted for known risk factors for stone disease. Urine urea nitrogen was used as a surrogate for dietary protein intake.
Results: 460 patients were included in the study. Female:male ratio was 184:276 (i.e. 40% female), mean age was 52.4 years (SD 14.3), mean BMI was 28.7 (SD 6.3). Mean 24-hour urine urea nitrogen was 12.1 g/day (SD 4.5). On multivariate linear regression, increasing dietary protein intake was significantly associated with increasing urine calcium (β = 4.53, 95% CI 0.51 to 8.54), uric acid (β = 0.012, 95% CI 0.007 to 0.018), sodium (β = 1.45, 95% CI 0.85 to 1.96), and volume (β =0.073, 95% CI 0.04 to 0.10). Increasing dietary protein was also significantly associated with decreasing urine citrate (β =-23.3, 95% CI -34.8 to -11.8) and pH (β =-0.05, 95% CI -0.07 to -0.04). There was no association between protein intake and urine oxalate.
Conclusions: Among known risk factors for nephrolithiasis, increasing dietary protein intake appears to increase urine calcium and uric acid, while decreasing urine citrate and pH. Restriction of protein intake, therefore, should reduce patient risk for both calcium oxalate and uric acid nephrolithiasis.