The reduction in postprandial lipemia after exercise is independent of therelative contributions of fat and carbohydrate to energy metabolism duringexercise

A single session of exercise several hours before a high-fat meal reduces p ostprandial lipemia. The purpose of the present study was to test the hypot hesis that this effect is independent of substrate metabolism during exerci se. 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 dai ly living were allowed the preceding day (control). On the other two occasi ons, subjects ran on a treadmill for 90 minutes on the afternoon preceding the fat tolerance test; 90 minutes before running, they ingested either aci pimox, an inhibitor of lipolysis in adipose tissue, or placebo. Acipimox ab olished the increase in the nonesterified fatty acid (NEFA) concentration o bserved 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 t he fasted state and for 6 hours after consumption of a high-fat meal (per k ilogram of body mass: 1.2 g fat, 1.2 g carbohydrate, and 61 kJ energy). Pla sma concentrations of NEFA were higher postprandially with acipimox, compar ed with control and placebo (P < .05), as were glucose concentrations measu red over the first 4 hours. The insulin response to the meal was lower in p lacebo compared with control and acipimox (P < .05). Despite these counterr egulatory responses, postprandial lipemia was reduced to the same degree (c ompared with control, P < .05) by exercise preceded by acipimox and by exer cise preceded by placebo (area under the plasma triacylglycerol concentrati on v time curve: control, 8.77 +/- 1.17 mmol/L . 6 h; placebo, 6.95 +/- 0.9 7 mmol/L . 6 h; acipimox, 6.81 +/- 0.81 mmol/L . 6 h). These findings sugge st that some factor other than the nature of the metabolic substrate used d uring exercise determines the attenuating effect of prior exercise on postp randial lipemia. Copyright (C) 1999 by W.B. Saunders Company.