Increased rates of meal absorption do not explain elevated 1-hour glucose in subjects with normal glucose tolerance

Context: In subjects with normal fasting glucose (NFG) and normal glucose tolerance (NGT), glucose concentrations .155 mg/dL 1 hour after 75 g of oral glucose predict increased risk of progression to diabetes. Recently, it has been suggested that the mechanism underlying this abnormality is increased gut absorption of glucose. Objective: We sought to determine the rate of systemic appearance of meal-derived glucose in subjects classified by their 1-hour glucose after a 75-g oral glucose challenge. Design: This was a cross-sectional study. Participating subjects underwent a 75-g oral glucose challenge and a labeled mixed meal test. Setting: An inpatient clinical research unit at an academic medical center. Participants: Thirty-six subjects with NFG/NGT participated in this study. Interventions: Subjects underwent an oral glucose tolerance test. Subsequently, they underwent a labeled mixed meal to measure fasting and postprandial glucose metabolism. Main Outcome Measures: We examined βcell function and the rate of meal appearance (Meal Ra) in NFG/NGT subjects. Subsequently, we examined the relationship of peak postchallenge glucose with Meal Ra and indices of βcell function. Results: Peak glucose concentrations correlated inversely with βcell function. No relationship of Meal Ra with peak postchallenge glucose concentrations was observed. Conclusion: In subjects with NFG/NGT, elevated 1-hour peak postchallenge glucose concentrations reflect impaired βcell function rather than increased systemic meal appearance.