The effects on renal function of moderate restriction in protein intake were studied in 14- to 20-yr-old type I diabetic patients who had no clinical renal disease or hypertension; matched normal subjects served as controls. After assessment of protein intake and renal function, studies were conducted at the completion of each of two consecutive dietary periods of 1 wk. Diets containing 3.5 and 1.5 g · kg−1 · day1 protein were provided during the first and second periods, respectively. Baseline protein intakes were substantial in both controls (1.86 g · kg−1 · day1) and diabetics (2.17 g · kg−1 · day1). Baseline creatinine clearance was increased in diabetics (P < .043). At the end of the highprotein intake period, both diabetics and controls showed similar high values of glomerular filtration rate (GFR) and renal plasma flow (RPF). GFR and RPF decreased markedly (P < .001) and to a similar degree in both groups after normal protein intake. GFR and RPF in diabetics were not higher than in controls at this point, but filtration fraction was increased in diabetics. Albumin excretion rates were similar in both groups and not influenced by renal function changes. GFR and RPF values correlated significantly with the quantity of protein intake, as estimated from the urea nitrogen appearance rate in both groups. The results suggest that the functional response to variations in protein intake is not altered in the diabetic kidney. In addition, increased renal function in diabetics may be related partly to the excessive protein content in commonly prescribed diabetic diets. Moderate dietary protein restriction is an additional approach for the correction of diabetic hyperfiltration.

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