Substituting milk for apple juice does not increase kidney stone risk in most normocalciuric adults who form calcium oxalate stones

Abstract

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 micromol/day on their self-selected diet.

Design: Randomized crossover trial.

Intervention: Each participant consumed two moderate-oxalate (2,011 micromol/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<.0001) on the milk diet vs the juice diet: 423 vs 514 micromol, respectively. Calcium excretion was 17% higher (P<.05) on the milk vs juice diet: 4.7 vs 3.9 mmol, respectively. Urinary magnesium and citrate excretion, volume, and Tiselius risk index did not differ between diets.

Applications: Substituting 360 mL milk daily for apple juice with meals in a diet containing moderate amounts of dietary oxalate from whole grains, legumes, fruits, and vegetables does not increase the risk index of calcium oxalate precipitability in most normocalciuric adults who form stones.