Low-protein diet and kidney function in insulin-dependent diabetic patients with diabetic nephropathy

BACKGROUND: Initiation of a low-protein diet (LPD) in patients with various nephropathies induces a faster initial and slower subsequent decline in the glomerular filtration rate (GFR). Whether this initial phenomenon is reversible or irreversible remains to be elucidated.

METHODS: We performed an eight-week prospective, randomized, controlled study comparing the effect of an LPD with a normal-protein diet (NPD) in 29 insulin-dependent diabetic patients with diabetic nephropathy. At baseline, the patients were randomized to either an LPD (0.6 g.kg-1.24 hr-1, LPD group, N = 14) or their NPD (NPD group, N = 15) for four weeks (phase I). Between weeks 4 and 8, all patients received their NPD (phase II, recovery). Dietary protein intake (g.kg-1.24 hr-1), GFR (51Cr-EDTA, ml.min-1.1.73 m-2), albuminuria (enzyme-linked immunoadsorbent assay, mg.24 hr-1), and arterial blood pressure (Hawksley random zero sphygmomanometer, mm Hg) were measured at baseline and after four- and eight-weeks of follow-up. During the investigation, all patients in the LPD group (N = 12) and in the NPD group (N = 14) received their usual antihypertensive treatment.

RESULTS: At baseline, the LPD group and the NPD group were comparable regarding dietary protein intake, GFR, albuminuria, and arterial blood pressure. During phase I, a significant decline in dietary protein intake, GFR, and albuminuria (mean, 95% CI) was observed in the LPD group [0.4 (0.3 to 0.5) g.kg-1.24 hr-1, 8.6 (3.2 to 13.9) ml.min-1.1.73 m-2, and 28.7 (14.0 to 40.9)%, respectively] compared with the NPD group [0.0 (-0.1 to 0.2) g.kg-1.24 hr-1 (P < 0.0001 between diets), 2.5 (-1.8 to 6.8) ml.min-1.1.73 m-2 (P = 0.07 between diets), and 0.0 (-20.1 to 23.5)% (P < 0.05 between diets), respectively]. Conversely, during phase II, a significant increase in dietary protein intake, GFR, and albuminuria [mean, 95% CI; 0.3 (0.2 to 0.5) g.kg-1.24 hr-1, 5.9 (0.8 to 11.1) ml.min-1.1.73 m-2, and 25.0 (4.5 to 49.6)%, respectively] took place in the LPD group compared with the NPD group [0.0 (-0.2 to 0.1) g.kg-1.24 hr-1 (P < 0.0001 between diets), -2.9 (-6.4 to 0.6) ml.min-1.1.73 m-2 (P < 0.01 between diets), and 2.9 (-18.3 to 29.7)% (P = 0.16 between diets), respectively]. Arterial blood pressure was comparable in the two groups of patients during phase I and II.

CONCLUSIONS: Dietary protein restriction for four weeks induces a reversible decline in GFR and albuminuria in insulin-dependent diabetic patients with diabetic nephropathy, whereas systemic blood pressure remains unchanged.