This study determined whether reductions in postprandial plasma nonesterified fatty acid (FFA) flux would lead to reductions in plasma acylcarnitine (AC) concentrations. Plasma AC was measured by liquid chromatography with tandem mass spectrometry in the fasting state and over 6 hours after a high-fat (50% energy) meal was fed to 16 overweight and obese subjects with a wide range of insulin sensitivities. Body composition was measured by dual-energy x-ray absorptiometry; insulin sensitivity by insulin-modified, frequently sampled intravenous glucose tolerance test; substrate oxidation by indirect calorimetry; blood metabolite and hormone concentrations biochemically; and fatty acid flux by using stable isotope tracers. Lean body mass and fasting fat oxidation correlated positively (r > 0.522, P < .05), whereas glucose oxidation correlated negatively (r < -0.551, P < .04), with fasting AC. Postprandially, plasma glucose, insulin, and triglyceride concentrations increased; and FFA concentrations decreased significantly. The responses of plasma AC species depended on chain length and saturation, with C14:0, C16:0, and C18:0 remaining unchanged, and unsaturated species (eg, C14:1, C14:2) falling significantly (21%-46%, P < .03). Postmeal nadir AC concentrations were positively associated with lean body mass, postprandial fatty acid flux, and FFA concentrations (r > 0.515, P < .05). By contrast, nadir AC correlated negatively with insulin sensitivity and spillover of meal-derived fatty acids (r < -0.528, P < .04). Conditions that impact fatty acid flux contribute to the control of postprandial plasma AC concentrations. These data underscore the need for a better understanding of postprandial fatty acid oxidation and dietary fat delivery in the setting of adipose insulin resistance to determine how postprandial lipemia contributes to chronic disease risk.
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