The Effect of Dietary Phosphate Load on Urinary Supersaturation and Phosphate Metablism in Non-stone-forming Asian Individuals.

Abstract

Introduction Phosphate ion is common in the core of urinary stones and may initiate stone formation. However, the precise role of phosphate in the initiation of stone formation remains obscure. We assessed the effects of dietary phosphate load on urinary stone risk and phosphate metabolism. Methods Ten non-stone-forming healthy volunteers completed this randomized, crossover study. Each subject was provided a high or low phosphate diet for 3 days. After a 2-day equilibration period with a moderate phosphate diet, the participants received a low or high phosphate diet for another 3 days. Serum, fecal and 24-hour urine samples were collected at the end of each intervention. Results High dietary phosphate load increased urinary phosphate excretion, and low dietary phosphate decreased urinary phosphate excretion. In addition, urine pH was lower and supersaturation index of uric acid was higher after high a phosphate diet. There was no significant difference in the supersaturation index for calcium oxalate, brushite and hydroxyapatite, or in 24-hour urinary citrate between the high and the low dietary phosphate. Also, no significant change was observed in fecal phosphate excretion after a high or low phosphate diet. The serum phosphate level increased after a high phosphate diet, but there was no difference in serum phosphate between low phosphate and moderate phosphate diets. Conclusion High dietary phosphate load led to higher urinary phosphate excretion, a higher supersaturation index of uric acid, and lower urine pH. Stone formers should be advised to limit the intake of high phosphate source diet, including high protein diets and phosphate-based food additives.