Postprandial metabolic flexibility during an oral glucose tolerance test in adults with excess body weight and/or excess adiposity: a sex-based comparison using indirect calorimetry.

BACKGROUND AND AIMS: Sex-related differences in postprandial metabolism remain incompletely understood, particularly in individuals with excess body weight or excess adiposity. This study aimed to compare postprandial metabolic responses between females and males with excess body weight or excess adiposity during a 75-g oral glucose tolerance test (OGTT) using indirect calorimetry and measuring circulating biomarkers. METHODS: In this cross-sectional study, 69 adults (26 females and 43 males) underwent a standardized OGTT after an overnight fast. Energy metabolism was assessed using a Q-NRG indirect calorimeter (COSMED, Rome, Italy) with a ventilated canopy system, and body composition was assessed using tetrapolar bioelectrical impedance analysis. Metabolic variables were assessed after fasting and at 60, 120, 180, and 240 min after glucose ingestion. The outcomes included non-protein substrate oxidation rates, respiratory exchange ratio (RER), energy expenditure, oxygen consumption ( O2), carbon dioxide production ( CO2), and circulating glucose and lactate levels. The incremental area under the curve (iAUC) was calculated to summarize the responses. RESULTS: Substrate utilization shifted from lipid to carbohydrate oxidation during the OGTT (time effect, all P<0.01). RER, energy expenditure, O2, CO2, glucose, and lactate also changed significantly over time (all P<0.01). Males had higher O2 and CO2 than females (both P<0.001), whereas no significant sex or time-by-sex interactions were observed for substrate oxidation, energy oxidation, RER, glucose, or lactate. The iAUC analyses showed no significant between-sex differences. Sensitivity analyses adjusting iAUC outcomes for relative glucose dose (per kg lean mass and per kcal REE) confirmed the absence of sex differences. CONCLUSIONS: No moderate-to-large sex differences in postprandial metabolic responses were detected in adults with excess body weight or excess adiposity.