β-cell function, incretin response, and insulin sensitivity of glucose and fat metabolism in obese youth: Relationship to OGTT-time-to-glucose-peak

BackgroundIn adults, the time-to-glucose-peak at or after 30minutes during an oral glucose tolerance test (OGTT) identifies physiologically distinct groups with differences in insulin sensitivity, beta-cell function and risk for type 2 diabetes. In obese non-diabetic adolescents, we investigated if the OGTT-time-to-glucose-peak also reflects incretin and free fatty acid (FFA) responses besides insulin sensitivity and beta-cell function, measured by the clamp. MethodsObese adolescents (n = 278) were categorized according to their OGTT-time-to-glucose-peak by Early-peak (at 30minutes) vs Late-peak (>30minutes) groups. Body composition, visceral adipose tissue, oral disposition index and OGTT-area under the curve (AUC) were examined. A subset of 102 participants had both hyperinsulinemic-euglycemic and hyperglycemic clamps to measure in vivo insulin sensitivity, insulin secretion, and beta-cell function relative to insulin sensitivity. ResultsCompared with the Early-peak group, the Late-peak group had impaired beta-cell function relative to insulin sensitivity, lower glucose-dependent insulinotropic polypeptide-AUC, and higher FFA-AUC despite higher insulin- and C-peptide-AUC. They also had lower hepatic and peripheral insulin sensitivity despite similar percent body fat and visceral adipose tissue, and had higher prevalence of impaired glucose tolerance (all P<.05). ConclusionsIn obese non-diabetic youth, those with a Late-peak vs an Early-peak glucose during an OGTT showed diminished beta-cell function, blunted incretin secretion, and lower insulin sensitivity of glucose and FFA metabolism. It remains to be determined if Late-peak glucose predicts the future development of type 2 diabetes in these high-risk youth.