Acute effects of moderate dietary protein restriction in patients with idiopathic hypercalciuria and calcium nephrolithiasis

Background: High dietary protein intake is a potential risk factor for neph rolithiasis because of its capacity to increase urinary calcium and to faci litate lithogenesis through many other mechanisms. Objective: Our aim was to verify the effects of moderate protein restrictio n in hypercalciuric patients. Design: We studied 18 patients (10 men and 8 women aged 45.6 +/- 12.3 y) wi th idiopathic hypercalciuria and renal calculi. Before and after 15 d of a diet with 0.8 g protein.kg(-1).d(-1) and 955 mg Ca, all patients were evalu ated for the main serum and urinary measures of calcium metabolism as well as for urinary uric acid, oxalate, citrate, and prostaglandin E-2. Results: Urinary excretion of urea fell after the diet (P < 0.001). Urinary calcium (P < 0.001), uric acid (P < 0.005), oxalate (P < 0.01), and hydrox yproline (P < 0.01) decreased after protein restriction, whereas urinary ci trate increased (P < 0.025), Blood pH increased after the hypoproteic diet (P < 0.05), 1,25-Dihydroxycholecalciferol (calcitriol) concentration fell s ignificantly (P < 0.025) and parathyroid hormone increased (P < 0.001). Cre atinine clearance tended to decrease (106.4 +/- 4.8 compared with 97.5 +/- 5.7 mL/min) after the diet. The decrease in urinary uric acid after the die t correlated with calcitriol concentration (r = 0.57, P < 0.05) and the dec rease in urinary urea correlated positively with that in hydroxyproline exc retion (r = 0.58, P < 0.01), Conclusions: In hypercalciuric patients, moderate protein restriction decre ases calcium excretion, mainly through a reduction in bone resorption and r enal calcium loss; both are likely due to a decreased exogenous acid load. Moreover, dietary protein restriction ameliorates the entire lithogenic pro file in these patients.