The effects of carbohydrate variation in isocaloric diets on glycogenolysis and gluconeogenesis in healthy men

To evaluate the effect of dietary carbohydrate content on postabsorptive gl ucose metabolism, we quantified gluconeogenesis and glycogenolysis after 11 days of high carbohydrate (85% carbohydrate), control (44% carbohydrate), and very low carbohydrate (2% carbohydrate) diets in six healthy men. Diets were eucaloric and provided 15% of energy as protein. Postabsorptive gluco se production was measured by infusion of [6,6-H-2(2)]glucose, and fraction al gluconeogenesis was measured by ingestion of (H2O)-H-2. Postabsorptive g lucose production rates were 13.0 +/- 0.7, 11.4 +/- 0.4, and 9.7 +/- 0.4 mu mol/kg.min after high carbohydrate, control, and very low carbohydrate die ts, respectively (P < 0.001 among the three diets). Gluconeogenesis was abo ut 14% higher after the very low carbohydrate diet (6.3 +/- 0.2 mu mol/kg.m in; P = 0.001) compared to the control diet, but was not different between the high carbohydrate and control diets (5.5 +/- 0.3 us. 5.5 +/- 0.2 mu mol /kg.min). The rates of glycogenolysis were 7.5 +/- 0.5, 5.9 +/- 0.3, and 3. 4 +/- 0.3 mu mol/kg.min, respectively (P < 0.001 among the three diets). We conclude that under eucaloric conditions in healthy subjects, dietary ca rbohydrate content affects the rate of postabsorptive glucose production ma inly by modulation of glycogenolysis. In contrast, dietary carbohydrate con tent affects the postabsorptive rate of gluconeogenesis minimally, as evide nced by only a slight increase in gluconeogenesis during severe carbohydrat e restriction.