Impact of gastric emptying to the glycemic and insulinemic responses to a 75‐g oral glucose load in older subjects with normal and impaired glucose tolerance

The majority of studies relating to the oral glucose tolerance test (OGTT) have not taken gastric emptying (GE), which exhibits a substantial inter‐individual variation, into account. We sought to evaluate the impact of GE, on the glycemic and insulinemic responses to a 75‐g oral glucose load in older subjects with normal and impaired glucose tolerance. Eighty‐seven healthy ‘older’ subjects (47F, 40M; age 71.0 ± 0.5 year) were given a drink comprising of 75‐g glucose and 150 mg C(13)‐acetate made up to 300 mL with water on a single occasion. Exhaled breath was obtained for analysis of (13)CO(2) and calculation of the 50% GE time (T(50)). Blood glucose, serum insulin and plasma glucagon‐like peptide‐1 (GLP‐1) and glucose‐dependent insulinotropic peptide (GIP) were measured, and the insulin sensitivity index (ISI), and the disposition index (DI), were calculated. Thirty‐one subjects had normal glucose tolerance (NGT) and 46 had impaired glucose tolerance (IGT). Blood glucose at t = 60 min and t = 120 min were related inversely to ISI (P < 0.001) and DI P < 0.001). The rise in blood glucose at t = 60 min was related inversely to the T(50) in all subjects (P < 0.01), and those with IGT (P < 0.001), but not NGT. There were no significant relationships between the blood glucose at t = 120 min with the T(50), but in both groups the change in blood glucose from baseline at t = 180 min was related (NGT: P < 0.001; IGT: P < 0.001) to the T(50). We conclude that in NGT and IGT, the effect of GE on both the ‘early’ and ‘late’ glycemic responses to a 75‐g oral glucose load is complementary to that of insulin sensitivity.