Comparison of peripheral glucose uptake after oral glucose loading and a mixed meal

Forearm glucose uptake (FGU) and other metabolic responses were studied in six normal men for three hours after a 75-g oral glucose load and a mixed meal containing 75 g carbohydrate. After the meal the rise in arterial glucose levels was considerably less than that following the oral glucose load but the overall insulin responses from 0 to 180 minutes were not statistically different. Although the initial rise in FGU was more gradual after the meal, the subsequent elevation was more sustained and, at the termination of the study, exceeded significantly that seen after the oral glucose load. The rise in GIP levels during the first hour was similar after the meal and the oral glucose load, but thereafter concentrations following the oral glucose load fell while those after the meal continued to rise. When the incremental area (Δ) is used as the index of response, the results show that while the glucose response (ΔG) after the meal (19.1 ± 5.3 units) was only 26% of that after oral glucose loading (72.7 ± 7.0 units), the corresponding increase in FGU (ΔFGU) reached 62% (55.0 ± 12.8 units after the meal, 89.2 ± 20.0 units after the oral glucose load). Thus, the increase in peripheral glucose uptake relative to the glycemic response (ΔFGUΔG) was significantly greater after the meal than following the oral glucose load alone (P < 0.05). In conclusion, relative to the rise in arterial glucose levels, peripheral glucose uptake is greater after a meal than after glucose loading with an equivalent carbohydrate challenge. Furthermore, the present data support previous studies emphasizing the failure of GIP alone to explain the entero insular axis.