Whole body fat oxidation increases during exercise. However 24-h fat oxidation on a day with exercise often remains similar to that of sedentary day, when energy intake is increased to achieve energy-balanced condition. The present study aimed to examine a possibility that time of the day when exercise is performed makes differences in 24-h fat oxidation. As a potential mechanism of exercise affecting 24-h fat oxidation, its relation to exercise-induced transient energy deficit was examined. Nine young male endurance athletes underwent three trials of indirect calorimetry using a metabolic chamber, in which they performed a session of 100 min exercise before breakfast (AM), after lunch (PM) or two sessions of 50 min exercise before breakfast and after lunch (AM/PM) at 65% of VO2max. Experimental meals were designed to achieve individual energy balance. Twenty-four-hour energy expenditure was similar among the trials, but 24-h fat oxidation was 1142±97, 809±88 and 608±46 kcal/24-h in descending order of its magnitude for AM, AM/PM and PM, respectively (P<0.05). Twenty-four-hour carbohydrate oxidation was 2558±110, 2374±114 and 2062±96 kcal/24-h, for PM, AM/PM and AM. In spite of energy-balanced condition over 24-h, exercise induced a transient energy deficit, magnitude of which was negatively correlated with 24-h fat oxidation (r=-0.72, P<0.01). Similarly, transient carbohydrate deficit after exercise was negatively correlated with 24-h fat oxidation (r=-0.40, P<0.05). The time of the day when exercise is performed affects 24-h fat oxidation, and the transient energy/carbohydrate deficit after exercise is implied as a factor affecting 24-h fat oxidation.
- energy balance
- energy flux
- metabolic chamber
- Copyright © 2014, Journal of Applied Physiology