STONE DISEASE

Effect of Dietary Modification on Urinary Stone Risk Factors
Pak CY, Odvina CV, Pearle MS, Sakhaee K, Peterson RD, Poindexter JR, Brinkley LJ
Center for Mineral Metabolism and Clinical Research and Department of Urology, University of Texas Southwestern Medical Center, Dallas, USA
Kidney Int. 2005; 68: 2264-73

• Background: This study was undertaken to ascertain the effect of dietary modification on urinary stone risks, and to determine whether the response depends on the prevailing urinary calcium.
• Methods: A retrospective data analysis was conducted from our stone registry involving 951 patients with calcareous stones undergoing ambulatory evaluation, whereby 24-hour urine samples were collected during random diet and after dietary modification composed of restriction of calcium, oxalate, sodium, and meat products. Samples were analyzed for stone risk factors. Urinary calcium was also obtained after overnight fast and following a 1 g-calcium load. Changes produced by dietary modification from the random diet were evaluated in 356 patients with moderate-severe hypercalciuria (> 6.88 mmol/day, group I), 243 patients with mild hypercalciuria (5.00-6.88 mmol/day, group II), and 352 with normocalciuria (< 5.00 mmol/day, group III).
• Results: Urinary calcium postcalcium load and the percentage of patients with absorptive hypercalciuria type I were highest in group I, intermediate in group II, and lowest in group III. During dietary modification, urinary calcium declined by 29% in group I, 19% in group II, and 10% in group III. Urinary oxalate did not change. Urinary saturation of calcium oxalate declined by only 12% in group I, 6% in group II, and nonsignificantly in group III, owing to various physicochemical changes in urinary biochemistry, which attenuated the effect of the decline in urinary calcium. Urinary saturation of brushite declined in all 3 groups due to the fall in urinary calcium, phosphorus, and pH. This reduction was more marked in the hypercalciuric groups than in the normocalciuric group. Urinary saturation of monosodium urate also decreased from a decline in urinary sodium and uric acid.
• Conclusion: Secondary rise in urinary oxalate occurring from calcium restriction can be avoided by concurrent dietary oxalate restriction. Dietary modification (restriction of dietary calcium, oxalate, sodium, and meat products) is more useful in reducing urinary saturation of calcium oxalate among patients with hypercalciuria than among those with normocalciuria.
  
  
• Editorial Comment
  The pendulum swings once more. Dietary restriction of calcium may play a select role in recurrent stone management. This study suggests that those who stand to benefit most from calcium restriction are those with urinary CA > 275 mg/day and those with calcium phosphate supersaturation. The authors correctly note that the addition of potassium citrate supplementation to dietary restriction of calcium may be important to have a significant impact on calcium oxalate saturation, as limiting dairy products alone will decrease the alkali load leading to lower pH and citrate levels. They also emphasize that calcium restriction should be part of a broad dietary intervention that also limits oxalate intake so as to avoid a compensatory increase in urinary oxalate due to increased bowel absorption. Though a diagnosis of absorptive hypercalcuria type I (AH1) was determined by a calcium load test, the authors did not stratify response to calcium restriction based on this diagnosis. However, almost 75% of patients with urinary CA > 275 mg/day were diagnosed with AH1. The authors propose that the use of a calcium-sparing diuretic and potassium citrate supplementation are additional important considerations to prevent a negative calcium balance with subsequent impact on bone density.

Dr. Manoj Monga
Professor, Department of Urology
University of Minnesota
Edina, Minnesota, USA