Maximizing postprandial energy expenditure and fat oxidation could be of clinical relevance for the treatment of obesity. This study investigated the effect of prior exercise on energy expenditure and substrate utilization after meals containing varying amounts of macronutrients. Eight lean (11.6% ± 4.0% body fat, M ± SD) and 12 obese (35.9% ± 5.3% body fat) men were randomly assigned to a protein (43% protein, 30% carbohydrate) or a carbohydrate (10% protein, 63% carbohydrate) meal. The metabolic responses to the meals were investigated during 2 trials, when meals were ingested after a resting period (D) or cycling exercise (Ex+D; 65% of oxygen consumption reserve, 200 kcal). Energy expenditure, substrate utilization, and glucose and insulin responses were measured for 4 hr during the postprandial phase. Although postprandial energy expenditure was not affected by prior exercise, the total amount of fat oxidized was higher during Ex+D than during D (170.8 ± 60.1 g vs. 137.8 ± 50.8 g, p < .05), and, accordingly, the use of carbohydrate as substrate was decreased (136.4 ± 45.2 g vs. 164.0 ± 42.9 g, p < .05). After the protein meal fat-oxidation rates were higher than after carbohydrate intake (p < .05), an effect independent of prior exercise. Plasma insulin tended to be lower during Ex+D (p = .072) and after the protein meal (p = .066). No statistically significant change in postprandial blood glucose was induced by prior exercise. Exercising before meal consumption can result in a marked increase in fat oxidation, which is independent of the type of meal consumed.
The authors are with the Dept. of Human and Health Sciences, University of Westminster, London W1W 6UW, UK.