Effects of carbohydrate-free diets on the insulin-carbohydrate relationships in rats

Insulin-carbohydrate relationships were investigated in four groups of young rats fed low protein diets differing in carbohydrate and fat contents: (1) a diet in which the nonprotein energy was provided by fatty acids (FA); (2) a similar diet in which the fatty acids were substituted by neutral fat (NF); (3) FA diet supplemented with glycerol (FA-Glyc); and (4) a carbohydrate-rich diet (HC). Control rats were fed a stock diet. Rats fed the FA diet lost weight, were hypoglycemic and hypoinsulinemic in the fed state and normoglycemic and normoinsulinemic in the fasted state, and had an impaired glucose tolerance and hyperinsulinemia after a glucose load. Liver and muscle glycogen were low in fed rats. Fasting increased glycogen in liver and decreased glycogen in muscle. NF animals gained weight, were hypoglycemic in both fed and fasted states, and their plasma glucose level after an oral glucose load was almost normal. Plasma insulin/glucose ratio, both in fed and fasted states and after a glucose load indicated hyperinsulinism, which was accompanied by obesity. Muscle and liver glycogen were low in fed animals and did not change after a fast. Supplementation of the FA diet with glycerol (FA-Glyc) abolished weight loss and fasting hyperglycemia and normalized plasma glucose and insulin response to a glucose load. Rats fed the HC diet had an improved glucose tolerance and an increased sensitivity to insulin. Liver glycogen was high in the fed state and normal in the fasted state, whereas muscle glycogen was normal in both nutritional states.