Effect of dietary modification on urinary stone risk factors.
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.


CONCLUSIONS
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.
Pak
Charles Y C
CY
Center for Mineral Metabolism and Clinical Research and Department of Urology, University of Texas Southwestern Medical Center, Dallas, 75390, USA. charles.pak@utsouthwestern.edu
Odvina
Clarita V
CV
Pearle
Margaret S
MS
Sakhaee
Khashayar
K
Peterson
Roy D
RD
Poindexter
John R
JR
Brinkley
Linda J
LJ
D000328:Adult; D002129:Calcium Oxalate / Q000652:urine; D002130:Calcium Phosphates / Q000652:urine; D002136:Calcium, Dietary / Q000652:urine; D005260:Female; D006801:Humans; D008297:Male; D008460:Meat; D008875:Middle Aged; D012042:Registries; D012189:Retrospective Studies; D012307:Risk Factors; D012982:Sodium, Dietary / Q000652:urine; D014527:Uric Acid / Q000652:urine; D014545:Urinary Calculi / Q000178:diet therapy* / Q000453:epidemiology* / Q000652:urine
D002130:Calcium Phosphates; D002136:Calcium, Dietary; D012982:Sodium, Dietary; D002129:Calcium Oxalate; D014527:Uric Acid; C494366:calcium phosphate, dibasic, dihydrate