Minor physiological relevance of oral glucose tolerance test

The physiological relevance of the oral glucose tolerance test was evaluated in ten healthy nonobese subjects and nine subjects with slightly impaired glucose tolerance. In random order, all subjects received a 50 g oral glucose tolerance test or a standardized breakfast meal of equivalent carbohydrate content. Changes in plasma glucose, insulin, and pancreatic glucagon concentrations were measured. In both groups, plasma glucose increased significantly during the oral glucose tolerance test and the meal test but the incremental glucose area (0-60 min) of the oral glucose tolerance test was about 350% and 120% greater than that of the mean test (p less than 0.001) in the normals and the patients with impaired glucose tolerance, respectively. In both groups, insulin responded almost similarly to the oral glucose tolerance test and the meal test whereas plasma glucagon declined significantly during the oral glucose tolerance test only (p less than 0.001). Glucagon remained unchanged during the meal test in the normals and increased slightly (p less than 0.05) in the group with impaired glucose tolerance. These data show that the response of glucose, insulin and glucagon to an oral glucose tolerance test in various respects is different to that obtained by the more physiological stimulation with a breakfast meal.