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 β-cell function and the rate of meal appearance (Meal R(a)) in NFG/NGT subjects. Subsequently, we examined the relationship of peak postchallenge glucose with Meal R(a) and indices of β-cell function. RESULTS: Peak glucose concentrations correlated inversely with β-cell function. No relationship of Meal R(a) with peak postchallenge glucose concentrations was observed. CONCLUSION: In subjects with NFG/NGT, elevated 1-hour peak postchallenge glucose concentrations reflect impaired β-cell function rather than increased systemic meal appearance.