The Effect of Modified Diets on Urinary Risk Factors in Kidney Stone Disease
It has been suggested that dietary therapy can manipulate the following urinary risk factors for calcium-oxalate stone disease: low urinary volume, hypercalciuria, hyperoxaluria, and hyperuricosuria. To address this issue, a two-part study was conducted. Part I investigated the effect of a modified fluid/calcium/oxalate/protein diet (MD) on urinary risk factors, and Part II determined if the addition of fiber (MD+F) would provide further benefit. A daily 10-g supplement of dietary fiber was supplied by two Fibermed biscuits (wheat and corn bran). Twenty-one hypercalciuric patients with calcium-oxalate stone disease were included in the study. Four-day food records (analyzed for 10 nutrients) and corresponding 24-h urine collections (analyzed for volume, calcium, oxalate, and uric acid) were assessed three times for each patient: an initial visit prior to any dietary intervention; following a three-month period on the MD; and following a four-week period on the MD+F. There were statistically significant decreases in the dietary energy, protein, fat, calcium, sodium, and oxalate, and an increase in water content following implementation of the MD. This resulted in a mean increase in 24-h urine volumes of 800 ml/day (p<0.001) and a non-significant decrease in the 24-h urinary calcium and oxalate excretion. The MD+F led to an average increase in dietary fiber from 5.9 g/day to 18.1 g/day (p<0.0001), an increase in dietary iron (p<0.0001), and a further reduction in dietary oxalate, but no other dietary changes occurred. The corresponding urine analysis showed a reduction in calciuria when compared to the initial visit (p<0.001) and to the period of MD alone (p<0.05). The 24-h urinary oxalate decreased from an initial value of 0.48 to 0.35 mmol (p<0.01), and urine volumes remained at the levels reported for the period of MD. Urinary uric-acid levels were unchanged following either diet.