Reduced Albuminuria After Dietary Protein Restriction in Insulin-Dependent Diabetic Patients With Clinical Nephropathy

Abstract

Recent clinical investigations have demonstrated that an early restriction of dietary protein intake may reduce the rate of progression of chronic renal failure in humans. In this study the effects of a restricted-protein diet on kidney function in type I diabetic patients with clinical nephropathy were evaluated. Sixteen patients (9 men, 7 women) with mean age 37.1 ± 9.8 yr, mean duration of diabetes 17.7 ± 6.6 yr, proteinuria > 0.5 g/24 h, and serum creatinine concentration of 0.7−1.9 mg/dl were studied. Patients were randomly divided into two groups. The low-protein diet (LPD) group comprised seven patients who were kept for 4.5 ± 1 mo on a diet containing 0.71 ± 0.12 g × kg−1 × day−1 protein. The normal-protein diet (NPD) group comprised nine patients as controls maintained for 11.7 ± 7 mo on their usual diabetic diet containing 1.44 ± 0.12 g × kg−1 × day−1 protein. All patients were studied every 1–2 mo. Metabolic control was assessed by evaluation of 5–8 blood glucose determinations/day and by glycosylated hemoglobin, whereas renal function was evaluated by albumin, IgG and β2-microglobulin urinary excretion rates, serum creatinine concentration, and creatinine clearance. At each visit, serum concentrations of total protein, albumin, phosphate, calcium, and electrolytes and weight and blood pressure were also measured. A significant reduction (434 ± 244 to 205 ± 212 μg/min, mean ± SD) in albumin excretion rate was found in all LPD patients after dietary protein restriction, with a significant reincrease (689 ± 201 μg/min) in the same patients several months after interruption of diet. In contrast, a significant increase in albumin (452 ± 200 to 850 ± 288 μg/min) and IgG (82 ± 63 to 129 ± 79 μg/min) urinary excretion rates was found in NPD patients. No significant variations were noticed during the study regarding creatinine clearance, serum creatinine, urinary β2-microglobulin, arterial blood pressure, and other parameters. Mean daily insulin requirements remained unchanged in all patients. We conclude that our study supports the hypothesis that diabetic nephropathy, like other forms of chronic renal disease, might benefit from an early restriction of dietary protein intake.