The reduction in postprandial lipemia after exercise is independent of the relative contributions of fat and carbohydrate to energy metabolism during exercise.

A single session of exercise several hours before a high-fat meal reduces postprandial lipemia. The purpose of the present study was to test the hypothesis that this effect is independent of substrate metabolism during exercise. Twelve men aged 21 to 36 years underwent three oral fat tolerance tests with intervals of at least 1 week. On one occasion, only activities of daily living were allowed the preceding day (control). On the other two occasions, subjects ran on a treadmill for 90 minutes on the afternoon preceding the fat tolerance test; 90 minutes before running, they ingested either acipimox, an inhibitor of lipolysis in adipose tissue, or placebo. Acipimox abolished the increase in the nonesterified fatty acid (NEFA) concentration observed during the run after placebo and reduced lipid oxidation (placebo, 37 +/- 7 g; acipimox, 21 +/- 3 g; P < .05, mean +/- SEM), but had no effect on gross energy expenditure (placebo, 4.86 +/- 0.20 MJ; acipimox, 4.83 +/- 0.18 MJ). Before each of the three fat tolerance tests, subjects reported to the laboratory after an overnight fast. Blood samples were obtained in the fasted state and for 6 hours after consumption of a high-fat meal (per kilogram of body mass: 1.2 g fat, 1.2 g carbohydrate, and 61 kJ energy). Plasma concentrations of NEFA were higher postprandially with acipimox, compared with control and placebo (P < .05), as were glucose concentrations measured over the first 4 hours. The insulin response to the meal was lower in placebo compared with control and acipimox (P < .05). Despite these counterregulatory responses, postprandial lipemia was reduced to the same degree (compared with control, P < .05) by exercise preceded by acipimox and by exercise preceded by placebo (area under the plasma triacylglycerol concentration v time curve: control, 8.77 +/- 1.17 mmol/L x 6 h; placebo, 6.95 +/- 0.97 mmol/L x 6 h; acipimox, 6.81 +/- 0.81 mmol/L x 6 h). These findings suggest that some factor other than the nature of the metabolic substrate used during exercise determines the attenuating effect of prior exercise on postprandial lipemia.