Diets with either beef or plant proteins reduce risk of calcium oxalate precipitation in patients with a history of calcium kidney stones.

OBJECTIVE: To determine the effect of substituting equal amounts of dietary protein as animal protein (beef) for plant protein (legumes, seeds, nuts, and grains) on urinary components associated with calcium oxalate precipitability risk. DESIGN: Randomized crossover trial. SUBJECTS: Twenty-three normocalciuric patients with a history of calcium kidney stones (8 women and 15 men, mean age 50.7+/-14.6 years) with 24-hour urinary calcium < or =10.3 micromol, 24 hour urinary oxalate excretion between 228 and 963 micromol, and a urinary calcium increase of < or =1.0 micromol in 4 hours after a 25 micromol oral calcium load. SETTING: Four-day, free-living adaptation period, followed by 2-day metabolic unit study. INTERVENTION: The study compared consumption of 2 servings of beef (43 g protein for women and 50 g for men) daily with an equal amount of protein from plant foods including legumes, nuts, and grains. MAIN OUTCOME MEASURES: Tiselius risk index (TRI) for calcium oxalate precipitability calculated from urinary calcium, oxalate, magnesium, citrate, and volume. STATISTICAL ANALYSES: Paired t tests. RESULTS: Urinary calcium, oxalate, magnesium, citrate, phosphorus, volume, and TRI did not differ between diets. Urinary sodium and potassium were higher for patients on the plant protein diet. After correcting for variations in urinary sodium and potassium between diets, the difference in urinary calcium remained insignificant. TRI was lower on both beef- and plant-protein diets compared with self-selected prestudy diets for all participants. CONCLUSION/APPLICATIONS: Balanced diets containing moderate amounts of either beef or plant protein are equally effective in reducing calcium oxalate kidney stone risk based on changes in urinary composition.

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 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.

Effect of caffeine on circadian excretion of urinary calcium and magnesium.

OBJECTIVE: To determine if later renal conservation occurs in calcium (Ca) and magnesium (Mg) excretion after morning caffeine-induced increases in urinary Ca and Mg excretion. DESIGN: Before-after trial of caffeine abstinance and consumption was conducted on two consecutive days in a metabolic ward while subjects ate a controlled diet containing 11.3 mmol Ca and 12.7 mmol Mg. 17 healthy males and females, ages 17-41 yr volunteered. Two caffeine doses of 3 mg/kg lean body mass caffeine were consumed at 7 and 10 a.m. on second day. Salivary caffeine concentrations and urinary Ca, Mg, sodium and creatinine excretion were measured. RESULTS: Salivary caffeine peaked at 4.7 umol/mL at 11:30 a.m. and declined with a half-life of 7.3 hours. Urinary Ca and Mg were elevated significantly (p = 0.01 and p = 0.04) for six h after the second caffeine dose. Caffeine had no significant effect on urinary calcium or magnesium excretion between 4 p.m. and 1 a.m. Between 1 and 4 a.m., urinary Ca and Mg excretion was decreased after caffeine (p = 0.04 and p = 0.01). Creatinine excretion was not different at any time. CONCLUSIONS: Nighttime compensatory renal conservation was insufficient to offset morning caffeine-induced mineral losses, resulting in net 24-hour urinary increases of 0.32 mmol Ca and 0.16 mmol Mg.

Effects of dietary calcium from dairy products on ambulatory blood pressure in hypertensive men.

The effect of consumption of 400 mg vs 1,500 mg of dietary calcium per day was examined in 13 male volunteers who had been diagnosed as hypertensive. Dietary calcium consumption was varied by manipulation of the intake of dairy products over 4-week periods. Caffeine intake (mean = 500 mg/day) was monitored. Neither laboratory blood pressure measured by standard sphygmomanometry nor ambulatory blood pressure monitored by automated sphygmomanometry varied significantly among men consuming baseline, low-calcium, or high-calcium diets (laboratory blood pressure = 136/83, 133/83, and 137/84 mm Hg, respectively; ambulatory blood pressure = 136/86, 138/87, and 138/87 mm Hg, respectively). Serum ionized calcium values did not vary with the three diets (1.25, 1.26, and 1.25 mmol/L, respectively). The parathyroid hormone level decreased (39 mmol/L vs 37 mmol/L) and the urinary calcium:creatinine ratio was elevated (0.41 vs 0.50) in the high-calcium diet. Consumption of a diet containing 1,500 mg calcium per day over 4 weeks did not produce a significant decrease in blood pressure or alterations in calcium metabolic indexes.