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Effect of short-term high-protein compared with normal-protein diets on renal hemodynamics and associated variables in healthy young men^1,2,3

¹ From Nephrology, Klinikum rechts der Isar (HF, RB, and UH), the Else Kroener-Fresenius Center for Nutritional Medicine (JG, UA-G, and HH), and the Molecular Nutrition Unit (HD), Technical University Munich, Munich, Germany.

² Supported by Else Kröner Fresenius-Stiftung, Bad Homburg, Germany.

³ Address correspondence to H Frank, Nephrology Department, Klinikum rechts der Isar, Technical University Munich, Ismaninger Strasse 22, 81675 Munich, Germany. E-mail: helga.frank{at}lrz.tum.de.

Background: High-protein diets are effective for weight reduction; however, little is known about the potential adverse renal effects of such diets.

Objective: The aim of our study was to compare the effect of a high-protein (HP) with a normal-protein (NP) diet on renal hemodynamics and selected clinical-chemical factors.

Design: We prospectively studied the effect of an HP diet (2.4 g · kg^–1 · d^–1) with that of an NP diet (1.2 g · kg^–1 · d^–1) on the glomerular filtration rate (assessed on the basis of sinistrin—an inulin analog—clearance) and renal plasma flow (para-aminohippuric acid clearance) by using the constant infusion technique. Filtration fraction and renal vascular resistance were calculated. Twenty-four healthy young men followed the 2 diet protocols for 7 d each in a crossover design. They were individually advised by a dietitian to achieve the planned protein intake by selecting normal foods under isocaloric conditions. Serum and urinary variables and renal hemodynamics were measured on day 7 of both diets.

Results: The glomerular filtration rate (NP: 125 ± 5 mL/min; HP: 141 ± 8 mL/min; P < 0.001) and filtration fraction (NP: 23 ± 5%; HP: 28 ± 5%; P < 0.05) increased significantly with the HP diet. Renal plasma flow was not significantly different between the HP (496 ± 25 mL/min) and NP (507 ± 18 mL/min) phases. Renal vascular resistance was not significantly different between the NP (94 ± 6 mm Hg · mL^–1 · min^–1) and HP (99 ± 8 mm Hg · mL^–1 · min^–1) phases. Blood urea nitrogen, serum uric acid, glucagon, natriuresis, urinary albumin, and urea excretion increased significantly with the HP diet.

Conclusions: A short-term HP diet alters renal hemodynamics and renal excretion of uric acid, sodium, and albumin. More attention should be paid to the potential adverse renal effects of HP diets.