Presentation Authors: Carter Boyd*, John Knight, Ross Holmes, Dean Assimos, Kyle Wood, BIRMINGHAM, AL
Introduction: Urinary oxalate levels are affected by both dietary and endogenous components. Prior studies have demonstrated the positive correlation between weight/body mass index (BMI) and urinary oxalate excretion. Our objective was to determine if this association is secondary to increased endogenous oxalate synthesis.
Methods: Healthy subjects, between 18 and 65 years old, with variable BMI were recruited. Subjects of various BMIs were recruited. Subjects consumed a low oxalate controlled diet containing 16% protein, 30% fat, 54% carbohydrate, 1000 mg calcium, and 30 mg oxalate which was devoid of vitamin C and calcium supplements. This diet limits the contribution of diet to the urinary oxalate pool. Subjects remained on this diet for 3 days. 24-hour urine collections were performed on the last two days. Urinary oxalate was measured by ion chromatography coupled with mass spectroscopy. Statistical analysis included Chi-squared, correlation and linear regression analysis, and student t-test.
Results: There were 41 subjects recruited with various BMIs (19-42). Urinary oxalate excretion (mg/day) was positively correlated with BMI (r=0.44, p=0.004) and waist circumference (r=0.42, p=0.006). Similar correlations were see with urinary glycolate excretion (mg/day) with BMI (r=0.41, p=0.007) and waist circumference (r=0.36, p=0.02). Urinary oxalate and glycolate excretion was positively correlated (r=0.31, p=0.049).
Conclusions: These results demonstrate a positive correlation between urinary oxalate derived from endogenous oxalate synthesis and BMI as well as other measures of obesity. This also provides an explanation for the association between stone risk and obesity.
Source of Funding: AUA Research Scholar/Medical Student Summer Fellowship; NORC Intramural Grant; K-08