The influence of macronutrient content of a meal on postprandial fatty acid oxidation was investigated in 13 Caucasian males after consumption of a high-fat (HF) breakfast (33% carbohydrate, 52% fat, 15% protein) and after an equicaloric high-carbohydrate (HC) breakfast (78% carbohydrate, 6% fat, 15% protein). The HF breakfast contained short- and medium-chain fatty acids, as well as long-chain fatty acids. Respiratory quotient (RQ) and plasma beta-hydroxybutyrate (BHB) were measured during the 3 h after the meal as indicators of whole body substrate oxidation and hepatic fatty acid oxidation, respectively. Plasma levels of free fatty acids (FFA), triglycerides, glucose, insulin, and lactate were also determined because of their relationship to nutrient utilization. RQ was significantly lower and plasma BHB was higher after the HF breakfast than after the HC breakfast, implying that more fat is burned in general and specifically in the liver after an HF meal. As expected, plasma FFA and triglycerides were higher after the HF meal, and insulin and lactate were higher after the HC meal. In sum, oxidation of ingested fat occurred in response to a single HF meal.