Research Department of Human Nutrition, The Royal Veterinary and Agricultural University, Copenhagen, Denmark.
BACKGROUND: Due to the high satiating effect of protein, a high-protein diet may be desirable in the treatment of obesity. However the long-term effect of different levels of protein intake on renal function is unclear. OBJECTIVE: To assess the renal effects of high vs low protein contents in fat-reduced diets. DESIGN: Randomized 6 months dietary intervention study comparing two controlled ad libitum diets with 30 energy (E%) fat content: high-protein (HP; 25 E%) or low-protein, (LP, 12 E% protein). All food was provided by self-selection in a shop at the department, and high compliance to the diet composition was confirmed by measurements of urinary nitrogen excretion. SUBJECTS: 65 healthy, overweight and obese (25<body mass index (BMI)<34 kg/m2). RESULTS: Dietary protein intake changed from 91.1 g/d to a 6 months intervention average of 70.4 g/d (P<0.05) in the LP group and from 91.4 g/d to 107.8 g/d (P<0.05) in the HP group, producing changes in glomerular filtration rate (GFR) of -7.1 ml/min in the LP group and +5. 2 ml/min in the HP group (group effect: P<0.05). Kidney volume decreased by -6.2 cm3 in the LP group and increased by +9.1 cm3 in the HP group (P<0.05), whereas albuminuria remained unchanged in all groups. CONCLUSION: Moderate changes in dietary protein intake cause adaptive alterations in renal size and function without indications of adverse effects.