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Introduction: A single previous study demonstrated that dietary protein intake may be associated with urine oxalate excretion. We evaluated the relationship between dietary protein intake and urine oxalate excretion in a cohort of stone formers.
Materials & Methods: A retrospective review was performed of a metabolic stone database at a tertiary care academic hospital. Univariate and multivariate analysis was performed to evaluate the relationship between urine urea nitrogen (a known surrogate for dietary protein intake) and urine oxalate. Multivariate models adjusted for age, gender, body mass index, race, hypertension, diabetes, medications, and urinary constituents (volume, sodium, potassium, phosphorus, creatinine, sulfate, pH).
Results: Six hundred two (602) patients were evaluated. Mean age was 52.5 (SD 14.3), mean BMI was 28.3 (SD 6.8), gender prevalence was 37% female:63% male, 27% of patients had hypertension and 10% of patients has diabetes mellitus. Mean urine oxalate excretion was 38.5 mg/day (SD 15.3). On univariate linear regression, dietary protein intake (urine urea nitrogen) was significantly associated with urinary oxalate excretion (β = 1.48, 95% CI 1.24 to 1.73, p < 0.001). On multivariate logistic regression controlling for confounders, increasing quintile of dietary protein intake was associated with significant increases in urine oxalate excretion (p = 0.03 for trend).
Conclusions: Dietary protein intake appears to be significantly associated with urine oxalate excretion. Prospective metabolic studies would be useful to confirm this finding. These data may be used in the future to help counsel stone formers on appropriate dietary therapies.