Clin Nephrol. 1984 Dec; 22(6): 273-8.

The effect of dietary protein on cystine excretion in patients with cystinuria.

Rodman JS, Blackburn P, Williams JJ, Brown A, Pospischil MA, Peterson CM.

Seven patients with homozygous cystinuria were studied on a metabolic ward to determine the effect of dietary manipulation on urinary cystine excretion. Isocaloric diets were calculated based on body weight and activity. Balance studies were performed for 5 days on a low protein diet (9.4 +/- 1.0% total calories) with equal amounts of animal and plant protein sources and an additional 5 days on a high protein (27 +/- 3.0% of total calories) with 70% animal protein. A significant (p less than 0.01) decrease in the excretion of 1/2-cystine, histidine, 3-methylhistidine, 1-methylhistidine, lysine, and ornithine plus arginine occurred on the low protein diet. The mean excretion of 1/2-cystine on the high protein diet was 6.13 +/- 1.48 mMoles per 24 hours which decreased to 4.89 +/- 1.06 mMoles per 24 hours on the low protein diet (p less than 0.001). Thirty seven percent of urine collections during the study were less than 2 liters/24 hours despite the fact that patients were encouraged to drink enough fluid to make 3 liters of urine/24 hours. For patients whose customary diet is high in animal protein, a more vegetarian diet may significantly reduce urinary cystine excretion. Cystine excretion in patients with cystinuria may be significantly different from day to day if animal protein consumption is variable.