Effect of source of dietary carbohydrate on plasma glucose, insulin, and gastric inhibitory polypeptide responses to test meals in subjects with noninsulin-dependent diabetes mellitus.

Previous reports have documented the fact that plasma glucose and insulin responses can vary in response to the ingestion of different carbohydrate-rich foods. This has led to the creation of a "glycemic index," a classification of dietary carbohydrates on the basis of the relative rise in plasma glucose after the administration of the food in question as compared to a standard glucose challenge. In order to test the clinical utility of these observations, we evaluated plasma glucose, insulin, and gastric inhibitory polypeptide responses to four major sources of carbohydrate (potato, rice, spaghetti, lentil) as part of a conventional mixed meal in patients with noninsulin-dependent diabetes mellitus. Each test meal provided 40% of the subjects' calculated caloric requirement and contained 15% of total calories as protein, 40% as fat, and 45% as carbohydrate. The test carbohydrate represented 66% of total carbohydrate. The results indicated that plasma glucose concentrations after meals containing equal amounts of carbohydrate as rice, spaghetti, or lentil were similar and somewhat lower than meals containing potato. The plasma insulin responses to the four carbohydrate foods paralleled the glucose responses. Changes in gastric inhibitory polypeptide levels did not account for the effect of potato. These results are totally disparate from what would have been predicted by previously published values for the "glycemic index" of the four foods studied, and suggest that a "glycemic index" based on isolated challenges would have minimal clinical utility in efforts aimed at reducing postprandial hyperglycemia in patients with noninsulin-dependent diabetes mellitus.