Background/objectives: Exercise performed shortly before (that is, within half a day of) a high-fat meal is beneficial for stimulating fat oxidation after the meal and reducing postprandial triglycerides (TG). This benefit of exercise is unfortunately negated if the after-exercise food choice to replace the calories expended during exercise is one containing high-glycemic index (HGI) carbohydrates. We determined the effect of consuming low-glycemic index (LGI) carbohydrates after an exercise session on fat oxidation and TG after a subsequent high-fat meal.
Subjects/methods: Using a randomized, counterbalanced crossover design, 23 overweight or obese individuals (body mass index ⩾25 kg m(-2)) performed: walking exercise (90 min) at 1800 h followed by no meal (EX); exercise followed by a meal with LGI carbohydrates (that is, lentils, EX-LGI); exercise followed by a meal with HGI carbohydrates (that is, instant potatoes, white bread, EX-HGI); and a control condition with no exercise or meal. After a 10-h overnight fast, participants were given a standardized high-fat meal. Fat oxidation was estimated before and for 6 h after this meal from respiratory gas measures and TG determined from blood samples.
Results: Fat oxidation (mean±s.d.) was higher with EX (6.9±1.7 g h(-1)) than EX-HGI (6.3±1.6 g h(-1); P=0.007) and Control (5.9±1.7 g h(-1); P=0.00002), and EX-LGI (6.6±1.7 g h(-1)) was higher than Control (P=0.002). TG total area under the curve was 18-32% lower with EX and EX-LGI compared with control (P=0.0005 and P=0.0001, respectively) and EX-HGI (P=0.05 and P=0.021, respectively).
Conclusions: A meal containing HGI carbohydrates consumed after an evening exercise session cancels the beneficial effect of exercise for stimulating fat oxidation and lowering TG after a subsequent high-fat meal, whereas consuming a post-exercise meal with LGI carbohydrates retains the positive effect of exercise.