Reproducibility and determinants of the metabolic responses during a mixed‐meal tolerance test

Abstract

AbstractObjectiveThe aim of this study was to assess the reproducibility and physiological determinants of mixed‐meal tolerance tests (MMTTs) on glucose and insulin responses.MethodsWhile inpatients on a weight‐maintaining diet, 894 individuals (574 with normal and 267 with impaired glucose regulation and 53 with type 2 diabetes [T2D]) underwent 9‐hour MMTTs (breakfast and lunch; 30% weight‐maintaining diet each; 40% carbohydrate, 40% fat, and 20% protein). Total/incremental areas under the curve (AUC/iAUC) were calculated from MMTT plasma glucose/insulin concentrations. Acute insulin response (AIR) was quantified by intravenous glucose tolerance test and insulin action (M) via hyperinsulinemic‐euglycemic clamp. A subset had repeat MMTTs (median follow‐up = 1.4 years).ResultsIn individuals without T2D, for breakfast‐versus‐lunch reproducibility of glucose, AUCs were moderate (intraclass correlation coefficients [ICCs]: 0.44‐0.61), and iAUCs were poor (ICCs < 0.15). For repeated MMTTs, reproducibility of AUC/iAUCs was low (ICCs: 0.11‐0.36). For insulin, AUC reproducibility was high (ICCs > 0.70), and iAUCs were moderate (ICCs: 0.64‐0.71). For repeated MMTTs, ICC AUC/iAUCs were 0.34 to 0.54. In those with T2D, ICC glucose AUC/iAUCs were >0.80 and >0.50, respectively, and for insulin were <0.40. For repeated MMTTs, ICC glucose/insulin AUC/iAUCs were moderate. Glucose AUCs associated with M/AIR (partial Rs < −0.25), and insulin AUCs negatively/positively associated with M/AIR (partial Rs = −0.51/0.24).ConclusionsReproducibility of glucose/insulin responses to MMTTs varied by subtraction of fasting values, glucose status, and time. Insulin secretion and action explained ~20% of MMTT responses. The substantial variability in MMTT response requires consideration in studies using MMTT outcomes.