Objective: We have previously reported that prior exercise increases the oxidation of dietary monounsaturated fat in comparison to rest when the fat is given in a mixed meal 30 min following the completion of exercise. In this study, we determined whether the increase in dietary fat oxidation after exercise persisted when the time between exercise and fatty acid administration was lengthened.
Design: Six female subjects (age=24+/-0.1 y, BMI=21+/-1 kg/m2) were recruited for a total of six visits each. During three visits, a stationary cycle exercise session (1250 kJ) was performed at 65% VO2 peak in a whole-body calorimeter; while during three other visits, exercise was replaced with rest. Subjects received [1-13C]oleate and [d31]palmitate with a different meal at each visit: breakfast, lunch, and dinner.
Results: Dietary oleate oxidation following prior rest did not differ between dose times and was 36+/-3, 42+/-5, and 42+/-3% for the 13 h following breakfast, lunch, and dinner. Prior exercise resulted in greater oleate oxidation following all dose times than prior rest (P<0.01) being 52+/-4, 64+/-3, and 53+/-3% for the breakfast, lunch, and dinner dose. The oxidation was significantly greater following lunch than the other dose times (P<0.05). Prior exercise (1250 kJ) did not result in greater oxidation of palmitate; however, oxidation following prior exercise increased with later dose times (13+/-2, 23+/-2, and 23+/-3% for breakfast, lunch, and dinner; P<0.05) and following rest (18+/-2, 22+/-2, and 27+/-2% for breakfast, lunch, and dinner; P<0.005).
Conclusions: The increase in oleate oxidation when administered after early morning exercise was found to persist for all three meals of the day, with the greatest effect occurring for the lunch meal. Palmitate oxidation, while apparently resistant to the effects of 1250 kJ of prior exercise, increases when administered later in the day, suggesting a diurnal variation in the oxidation of dietary fatty acids. These results demonstrate that prior exercise selectively alters the partitioning of dietary fatty acids. Furthermore, these findings demonstrate additional benefits of substituting monounsaturated for saturated fatty acids in the diet.