Effects of high intake of dietary animal protein on mineral metabolism and urinary supersaturation of calcium oxalate in renal stone formers.

The metabolic effects of a high protein diet (HPD) were studied in eight patients with idiopathic recurrent calcium oxalate stones. On the HPD there was a 35% increase in urinary calcium concomitant with increased excretion of cyclic AMP and hydroxyproline. These findings point to an enhanced resorption of bone, possibly secondary to increased renal loss of calcium. The urinary citrate decreased by 25% along with reduced serum standard bicarbonate and urinary pH. The high formation of acid metabolites might also have adverse effects on calcium balance and bone. Urinary oxalate excretion was not affected nor were there any significant changes in the calculated urinary supersaturation of calcium oxalate, if changes in urinary citrate, pH, sulphate, sodium, phosphate and volume were also considered. This study suggests that the possible negative influence on the propensity to form renal stones of a diet rich in animal protein is probably due to reduced urinary inhibitory activity.