Substituting Milk for Apple Juice Does Not Increase Kidney Stone Risk in Most Normocalciuric Adults Who Form Calcium Oxalate Stones

Objective Increasing intake of dietary calcium from less than 400 mg to 800 mg daily may decrease the absorption of dietary oxalate, which in turn would decrease urinary oxalate excretion. The effect of substituting milk for apple juice on urine composition and risk of calcium oxalate precipitability was studied. Subjects Twenty-one normocalciuric adults with a history of at least 1 calcium oxalate stone and urinary oxalate excretion exceeding 275 μmol/day on their self-selected diet. Design Randomized crossover trial. Intervention Each participant consumed two moderate-oxalate (2,011 μmol/day) study diets, which were identical except that one contained 360 mL milk and the other contained 540 mL apple juice as the beverage with meals. Setting Four days free-living then 2 days in the metabolic unit of a university nutrition department. Main outcome measure Tiselius risk index for calcium oxalate precipitability calculated from urine composition. Statistical analyses Paired t tests. Results Twenty-four hour urinary oxalate excretion was 18% lower ( P