The influence of macronutrient content of a meal on postprandial fatty
acid oxidation was investigated in 13 Caucasian males after consumpti
on of a high-fat (HF) breakfast (33% carbohydrate, 52% fat, 15% protei
n) and after an equicaloric high-carbohydrate (HC) breakfast (78% carb
ohydrate, 6% fat, 15% protein). The HF breakfast contained short- and
medium-chain fatty acids, as well as long-chain fatty acids. Respirato
ry quotient (RQ) and plasma beta-hydroxybutyrate (BHB) were measured d
uring the 3 h after the meal as indicators of whole body substrate oxi
dation and hepatic fatty acid oxidation, respectively. Plasma levels o
f free fatty acids (FFA), triglycerides, glucose, insulin, and lactate
were also determined because of their relationship to nutrient utiliz
ation. RQ was significantly lower and plasma BHB was higher after the
HF breakfast than after the HC breakfast, implying that more fat is bu
rned in general and specifically in the liver after an HF meal. As exp
ected, 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.