A short-term low-protein diet reduces glomerular filtration rate in insulin-dependent diabetes mellitus patients.

1. The effect of a 7-day low-protein diet on renal function was studied in 17 normotensive, normoalbuminuric, insulin-dependent diabetes mellitus (IDDM) patients. Glomerular filtration rate (GFR) and urinary albumin excretion (UAE) were measured after 7 days on an isocaloric low-protein diet (0.5 g protein/kg per day). 2. Compliance was confirmed by 24-h urinary urea levels. GFR was measured after a single injection of 51Cr-EDTA and UAE by radioimmunoassay. 3. GFR was reduced by 13.8% on the low-protein diet (139.9 +/- 27.7 vs 120.4 +/- 25.1 ml min-1 (1.73 m2)-1) (P less than 0.05). This effect was of the same magnitude as that obtained by others after long-term strict metabolic control. No changes were observed in UAE (5.6 +/- 6.4 vs 5.7 +/- 6.8 micrograms/min) during the study. The patients were classified as hyperfiltering (N = 9; GFR = 160.3 +/- 16.6 ml min-1 (1.73 m2)-1) or normofiltering (N = 8; GFR = 117.1 +/- 17.6 ml min-1 (1.73 m2)-1) on the basis of GFR, and no difference in the reduction of GFR was observed in either group. 4. The reduction in GFR is probably caused primarily by the reduction of protein intake since other factors that might influence the GFR such as glucose control and blood pressure did not change during the study.