The aim of this study was to compare the metabolic effects of a high-carbohydrate (CHO), high-fiber diet with only moderate protein restriction with those of a low-CHO, low-fiber diet with a low protein content in six diabetic patients with moderate chronic renal failure. The high-CHO, high-fiber diet induced a significant improvement in blood glucose control, a significant decrease in serum cholesterol, and a significant increase in fecal nitrogen losses. Other variables evaluated were not significantly different between the two diets, except for a significant increase in serum phosphorus during the high-CHO, high-fiber diet. N balance was not significantly different from 0 at the end of either dietary period and was very similar for both diets. The high-CHO, high-fiber diet presents many beneficial metabolic effects in diabetic patients with chronic renal failure.