Objective: The aim of this study was to determine how training modifies metabolic responses and lipid oxidation in overweight young male subjects.
Research methods and procedures: Eleven overweight subjects were selected for a 4-month endurance training program. Before and after the training period, they cycled for 60 minutes at 50% of their VO(2)max after an overnight fast or 3 hours after eating a standardized meal. Various metabolic and endocrine parameters, and respiratory exchange ratio values were evaluated.
Results: Exercise-induced plasma norepinephrine concentration increases were similar before and after training in fasted or fed conditions. After food intake, exercise promoted a decrease in plasma glucose and a higher increase in epinephrine than in fasting conditions. The increase in epinephrine after the meal was more marked after training (264 +/- 32 vs. 195 +/- 35 pg/mL). Training lowered the resting plasma nonesterified fatty acids. During exercise, changes in glycerol were similar to those found before training. Lipid oxidation during exercise was higher in fasting than in fed conditions (15.5 +/- 1.4 vs. 22.3 +/- 1.7 g/h). Training did not significantly increase fat oxidation when exercise was performed in fed conditions, but it did in fasting conditions (18.6 +/- 1.4 vs. 27.2 +/- 1.8 g/h).
Discussion: Endurance training decreased plasma nonesterified fatty acids, cholesterol, and insulin concentrations. Training increased lipid oxidation during exercise, in fasting conditions, and not when exercise was performed after the meal. During exercise in overweight subjects, the fasting condition seems more suited to oxidizing fat and maintaining glucose homeostasis than a 3-hour wait after a standard meal.