Influence of dietary animal protein on renal stone disease

Abstract

The effect of dietary protein load on the incidence of nephrolithiasis was studied in rats and men. Three groups of adult male Wister rats were fed with a standard protein diet, a high protein diet, or a low protein diet for 4 weeks. In the high protein group, calcium excretion was significantly increased and citrate excretion was remarkably decreased. This group also exhibited low grade metabolic acidosis due to catabolism of excess amino acids, and increases in urinary cyclic AMP excretion and bone resorption. These findings indicate that protein-induced hypercalciuria is due to low grade metabolic acidosis, which directly affects renal handling of calcium. Long-term calcium loss in the urine may lead to negative calcium balance and hyperfunction of the parathyroid gland may induce bone resorption. The influence of 40 g animal protein load on urinary risk factors of calcium stone formation was investigated in 23 healthy males and 26 patients with nephrolithiasis. All subjects were given control diets each day containing 60 g protein for a week and during the next week each received an additional 40 g animal protein. In the controls, added dietary protein resulted in decreased urinary citrate and increased urinary uric acid, with no change in urinary calcium or cyclic AMP excretion. In contrast, the patients showed increased urinary calcium and cyclic AMP as well as decreased urinary citrate. Further examinaiton of the patients revealed that the significant increases of calcium and cyclic AMP excreton occurred only in hypercalciuric patients, who seemed to be classified into renal hypercalciuria. These results suggest that even 40 g animal protein affects citrate and uric acid metabolism in normal subjects and patients, and affects calcium metabolism in hypercalciuric patients. These findings indicate the importance of diet guidance to patients with nephrolithiasis, with special regard to the correction of excessive animal protein intake. © 1989, THE JAPANESE UROLOGICAL ASSOCIATION. All rights reserved.