EFFECT OF DIETARY-PROTEIN RESTRICTION ON FUNCTIONAL RENAL RESERVE IN DIABETIC NEPHROPATHY

purpose, patients, and methods: Functional renal reserve in patients with insulin-dependent diabetes mellitus, as determined by the glomerular filtration rate (GFR) response test, is a measure of the capacity of the kidney to increase glomerular filtration in response to the stimulus of a protein meal or amino acid infusion. This 12-month study evaluated the changes in functional renal reserve in eight patients with insulin-dependent diabetes mellitus with nephropathy (micro-albuminuria [greater than or equal to 30 μg/minute]) who chronically decreased their dietary protein intake to a mean of 0.6 g/kg/day (Group 1) compared with a group of similar patients (n = 7) who maintained their usual dietary protein intake (1.0 g/kg/day, Group 2). Patients were evaluated and measurements taken at 3-, 6-, and 12-month intervals. Absolute and percent increases in GFR were calculated from three averaged 1-hour measurements after an 80-g protein test meal. results: Although the initial absolute mean rise (14 ± 12 versus 18 ± 13 mL/minute/1.73 m2) in GFR and maximal percent rise (16% ± 16% versus 32% ± 27%) after the meal did not differ significantly between the two groups, at 12 months, values in the lower protein group increased (27.8 ± 9.5 mL/minute/1.73 m2 and 54.7% ± 48.8%), whereas those in the normal protein intake group declined significantly (3.7 ± 3.6 mL/min-ute/1.73 m2 and 6.5% ± 6.5%) (p <0.05). Both urine urea and microalbuminuria decreased significantly (p <0.05) in the low protein group. Unstimulated GFR at the end of 12 months was significantly less (p <0.05) in Group 2 (47 ± 2 mL/minute/1.73 m2) than in Group 1 (71 ± 21 mL/minute/1.73 m2). The rate of decline in GFR was significantly greater (p <0.05) in the normal protein intake group than in the low protein intake group (0.68 ± 0.4 versus 0.28 ± 0.15 mL/minute/1.73 m2/month). conclusion: This study indicates that sustained dietary protein restriction can help to preserve renal function, decrease albuminuria, and lower the baseline GFR while maintaining functional renal reserve in patients with insulin-dependent diabetes mellitus. © 1990.