Beneficial effects of low-carbohydrate-high-protein diets in long-term diabetic rats

Groups of streptozotocin-diabetic rats (65 mg/kg subcutaneously) were fed ad lib. on three different diets over 12 mo: a low-carbohydrate (CHO)-high-protein (6%:63% of calories) diet; a moderate-CHO-high-protein (27%:50%) diet; and a standard control diet (68% as CHO, 20% as protein). The 6%-CHO diet resulted in an initial decrease in nonfasting blood glucose from 550 to 280 mg/dl, followed by a further gradual improvement ending with blood glucose levels below 160 mg/dl and reduction of glycosuria to physiologic amounts. In the group fed the 27%-CHO diet, there was a similar initial decrease in blood glucose, but blood glucose values below 160 mg/dl after 12 mo were attained in only 3 of 8 rats. All rats fed the standard 68%-CHO diet maintained blood glucose levels between 500 and 650 mg/dl throughout. The late recovery in the low-CHO fed groups was associated with increased pancreatic insulin content. Animals fed low-CHO diets showed a better weight gain and improved general condition. The onset of cataracts as observed with the hand slit-lamp was regularly delayed in the animals on the 6%- and 27%-CHO diet; in some instances, it was entirely prevented. The threshold concentration of blood glucose seemingly required for onset of cataracts was about 300 mg/dl. Nerve sorbitol and fructose levels were clearly higher in hyperglycemic animals and correlated well with the severity of hyperglycemia. Thus, low-CHO-high-protein diets, which markedly improve hyperglycemia, may also improve at least some of the secondary changes usually seen in severely hyperglycemic rats.