Glucose curve morphology and peak time as biomarkers of metabolic health.

The oral glucose tolerance test (OGTT) is widely used to assess glucose tolerance, but the conventional 2-h postprandial glucose value faces limited reliability. Alternative OGTT-derived indices, such as the shape of the glucose curve and the time to glucose peak, may offer additional insights into metabolic health. This study examined whether these indices could serve as biomarkers of metabolic risk. Normoglycemic adults [n = 85 (males: 40; females: 45); age: 26.9 ± 4.6 yr; body mass index: 23.1 ± 2.4 kg/m2] underwent a 3-h OGTT, with repeated measurements of blood glucose, insulin, and free fatty acids (FFAs). Insulin sensitivity was assessed by hyperinsulinemic-euglycemic clamp. Energy expenditure (EE) and sleep respiratory quotient (RQ) were measured by metabolic chamber, and body composition by the EchoMRI-AH. Participants were classified by glucose curve morphology (monophasic vs. biphasic) and glucose peak time (early: ≤30 min vs. late: >30 min). Compared with the monophasic group, the biphasic group showed lower postprandial glucose (P < 0.05), with no differences in 3-h glucose area under the curve (AUC), insulin AUC, insulin sensitivity, FFA, EE, RQ, or body fat. In contrast, the early peak exhibited lower postprandial glucose, 3-h insulin AUC, 2-h FFA AUC, RQ, and body fat, with higher EE (P < 0.05) and a trend toward higher insulin sensitivity (P = 0.0592), compared with the late-peak group. Biphasic glucose curves and early glucose peak time indicate better glucose tolerance and insulin sensitivity. Compared with glucose curve morphology, glucose peak time demonstrated a stronger discriminative index of metabolic health and could serve as an additional biomarker of the OGTT for identifying potential diabetes risks.NEW & NOTEWORTHY Participants in biphasic groups showed better glucose tolerance than monophasic participants. Participants in early-peak groups showed better glycemic control and energy metabolism than late-peak participants. Glucose peak time demonstrates a stronger discriminative index of metabolic health than glucose curve morphology. Glucose peak time could serve as a useful biomarker of the OGTT for identifying potential diabetes risks.