Effect of dietary protein restriction and influence of proteinuria on progression of type 2 diabetic renal failure

Abstract

PURPOSE : This study investigated the effect of dietary protein restriction on disease progression and how it is influenced by proteinuria in patients with type 2 diabetic nephropathy (DN) and renal failure. METHODS : One hundred and six type 2 DN patients whose baseline creatinine clearance (Ccr) values were 29±12 ml/min/1.73 m² were maintained on a diet containing 0.66±0.05 g/kg/day of protein. They were classified into 3 groups according to mean dietary protein intake (DPI) estimated from urinary urea nitrogen excretion during the follow-up period of 23±14 months (I, <0.7 g/kg/day ; II, 0.7-0.89 g/kg/day ; III, ≥ 0.9 g/kg/day). Furthermore, they were divided into 3 subgroups according to mean urinary protein excretion (UP) during the follow-up period (a, ≥ 5.0 g/day ; b, 2.0-4.99 g/day ; c, <2.0 g/day) . Their rates of decline of Ccr (D-Ccr) and the changes in UP were examined. RESULTS : There were no significant differences in D-Ccr among Group Ia, IIa, and IIIa (1.1±0.6, 1.5±0.7, 1.2±0.6 ml/min/1.73 m²/month), among Group Ib, IIb, and IIIb (0.6±0.3, 0.7±±0.4, 0.8±0.4ml/min/1.73 m²/month), and also among Group Ic, IIc, and IIIc(0.1±0.3, 0.2±0.2, 0.2±0.6 ml/min/1.73 m²/month). On the other hand, significant differences were revealed in D-Ccr among Group Ia, Ib, and Ic, among Group IIa, IIb, and IIc, and among Group IIIa, IIIb, and IIIc. There were no significant differences in final UP and minimum UP during follow-up among 3 groups of different DPI levels in patients with 5.0 g/day≤baseline UP (n=49) and in patients with 2.0≤baseline UP<5.0 g/day (n=37).However, significant correlations were demonstrated between D-Ccr and the relative changes in UP between baseline and minimum during the follow-up period in both patients (r=0.49, 0.48, p<0.001, p <0.01). CONCLUSIONS : Irrespective of the level of dietary protein restriction, proteinuria has a great influence on disease progression, and the reduction in UP correlates with retardation of renal function loss in patients with type 2 DN and renal failure.