Potential renal acid load and the risk of renal stone formation in a case-control study.

OBJECTIVE: The potential renal acid load (PRAL) in diet may have a key role in renal stone formation through its effect on calcium and citrate metabolism. We examined the association between calcium renal stone formation and the PRAL in a population-based case-control study. METHODS: A group of 123 calcium renal stone formers was compared with an equal number of age- and sex-matched controls. Dietary history was obtained by 24-h recall. Odds ratios (ORs) and 95% confidence intervals (CI) were calculated across quartiles of dietary intakes of PRAL. RESULTS: Compared with those in the lowest quartiles of PRAL, we found an increased risk of renal stone formation for those in the highest quartile (Q4 OR=2.51, 95% CI 1.218-5.172). Regarding individual food patterns, we found a significant protection for a high consumption of vegetables (two or more servings/day; OR=0.526, 95% CI 0.288-0.962). CONCLUSIONS: A PRAL in diet and a reduced consumption of vegetables are associated with an increased risk of calcium renal stone formation. In renal stone formers consumption of plant foods should be encouraged in order to counterbalance the acid load derived from animal-derived foods.

Effect of acute load of grapefruit juice on urinary excretion of citrate and urinary risk factors for renal stone formation.

The effect of citrus fruit juice ingestion on the risk of calcium oxalate stone formation is still debated. The present study was undertaken to investigate changes in urinary stone risk factors after administration of a soft drink containing grapefruit juice. Seven healthy subjects, with no history of kidney stones, were submitted to an acute oral load (20 ml/kg body weight over 60 min) of a soft drink containing grapefruit juice diluted (10%) in mineral water. After a 7-day wash-out period, each subject underwent an oral load with mineral water alone under the same conditions. Urine specimens were collected before (for 120 min) and after each oral fluid load (for 180 min). Urinary flow was significantly increased after both grapefruit juice (46+/-26 vs 186+/-109 ml/h, p = 0.01) and mineral water (42+/-16 vs 230+/-72 ml/h, p=0.001) compared to baseline. Compared to mineral water, grapefruit juice significantly (p=0.021) increased urinary excretion of citrate (25.8+/-9.3 vs 18.7+/-6.2 mg/h), calcium (6.7+/-4.3 vs 3.3+/-2.3 mg/h, p=0.015) and magnesium (2.9+/-1.5 vs 1.0+/-0.7 mg/h, p=0.003). Citrus fruit juices could represent a natural alternative to potassium citrate in the management of nephrolithiasis, because they could be better tolerated and cost-effective than pharmacological calcium treatment. However, in order to obtain a beneficial effect in the prevention of calcium renal stones a reduced sugar content is desirable to avoid the increase of urinary calcium due to the effect of sugar supplementation.

Effect of potential renal acid load of foods on calcium metabolism of renal calcium stone formers.

OBJECTIVES: Diet has been proposed as a causative factor of hypercalciuria in patients with calcium stones. The aim of this study was to investigate the influence of diet on calcium metabolism of renal stone formers. METHODS: Thirty-five renal calcium stone formers were entered in this study. A 2-day recall of dietary intake was obtained from each subject. The food records were coded and computer analyzed for total energy, protein, fat, carbohydrate, sodium, potassium, calcium, magnesium, phosphate, oxalate, vitamin C and fiber. Daily potential renal acid load (PRAL) of the diet was calculated considering the mineral and protein composition of foods, the mean intestinal absorption rate for each nutrient and the metabolism of sulfur-containing amino acids. A fasting blood sample was drawn and a 24-hour urine collection were obtained for analyses of calcium, phosphate and creatinine. Serum osteocalcin was also analyzed. A fasting 2-hour urine sample was collected in the morning for hydroxyproline, pyridinium cross-links and creatinine. RESULTS: The mean daily dietary PRAL of renal stone formers was 22.4 +/- 15.7 (range 4.2-65.8) mEq/day. Regression analysis demonstrated that urinary calcium excretion is dependent on daily protein intake and dietary PRAL, whereas the urinary pyridinium cross-links/creatinine ratio is inversely dependent on daily calcium intake. The urinary pyridinium cross-links/creatinine ratio was significantly lower in patients on a low calcium diet (< 600 mg/day) than in other patients (19.5 +/- 7.8 vs. 27.3 +/- 7.5 nM/mM, p = 0.008). No significant difference was observed between the 2 groups for daily urinary calcium (254 +/- 109 vs. 258 +/- 140 mg/day), serum osteocalcin (8.2 +/- 3.3 vs. 6.2 +/- 2.4 ng/ml) and urinary hydroxyproline/creatinine (14.1 +/- 7.4 vs. 10.3 +/- 4 mg/g). CONCLUSIONS: The urinary calcium excretion of renal stone formers seems to be dependent on dietary acid load rather than dietary calcium intake. In patients consuming an acidifying diet a restriction of calcium intake could increase bone resorption leading to a progressive bone loss.