Effects of 5 different diets on urinary risk factors for calcium oxalate kidney stone formation: evidence of different renal handling mechanisms in different race groups.
OBJECTIVE
Since the incidence of renal calculi in the South African black population is extremely rare while in white subjects it occurs at the same rate as elsewhere in the western world, we investigated the possibility that different renal handling mechanisms in response to different dietary challenges might occur in the 2 race groups.


METHODS
We administered 5 different dietary protocols, including low calcium, high oxalate, vitamin C, high salt and lacto-vegetarian, to 10 healthy male subjects from each race group. We collected 24-hour urine at baseline and after 4 days on the prescribed diet which were analyzed for biochemical and physicochemical risk factors. Dietary intake was controlled throughout the experimental period. A 24-hour dietary recall questionnaire was recorded at baseline and analyzed using food composition tables. Statistical analysis of variance was performed on all the data.


RESULTS
The low calcium diet caused statistically significant changes only in black subjects, which consisted of urinary oxalate increase (0.17 to 0.23 mmol./24 hours, p = 0.01), relative supersaturation of calcium oxalate decrease (1.88 to 0.97, p = 0.03) and relative supersaturation of brushite increase (0.85 to 1.69, p = 0.03). The high oxalate diet caused statistically significant changes in both race groups but these changes were different in the 2 groups. In white subjects urinary pH increased (6.24 to 6.62, p = 0.01), potassium excretion increased (40.01 to 73.49, p = 0.01) and relative supersaturation of brushite increased (1.34 to 2.12, p = 0.05). In black subjects urinary citrate increased (1.94 to 2.99 mmol./24 hours, p = 0.01). Clinically unimportant changes occurred in both race groups after the other 3 diets.


CONCLUSIONS
Renal handling of dietary calcium and oxalate in South African black and white subjects is different and may explain the different stone incidence in the 2 race groups.
Department of Chemistry, University of Cape Town, South Africa.
Allen L
AL
Rodgers
Sonja
S
Lewandowski
D000293:Adolescent; D000328:Adult; D001205:Ascorbic Acid / Q000009:adverse effects; D044383:Black People; D002129:Calcium Oxalate / Q000032:analysis*; D002136:Calcium, Dietary / Q000009:adverse effects; D004032:Diet / Q000009:adverse effects*; D014676:Diet, Vegetarian / Q000009:adverse effects; D006801:Humans; D007668:Kidney / Q000378:metabolism*; D007669:Kidney Calculi / Q000737:chemistry / Q000209:etiology* / Q000378:metabolism; D008297:Male; D010070:Oxalates / Q000009:adverse effects; D044469:Racial Groups; D012307:Risk Factors; D012982:Sodium, Dietary / Q000009:adverse effects; D044465:White People
D002136:Calcium, Dietary; D010070:Oxalates; D012982:Sodium, Dietary; D002129:Calcium Oxalate; D001205:Ascorbic Acid