Objective: The aim of this study was to investigate the effects of an acute exercise bout in the morning in the post-absorptive or postprandial state on the glycemic and insulinemic response to three standardized meals throughout the day. It is hypothesized that post-absorptive exercise enhances fat oxidation rate during exercise and thereafter attenuates the glucose and insulin response to subsequent meals.
Research methods and procedures: Seven sedentary males with metabolic syndrome (age, 45 +/- 11 years; BMI, 34 +/- 3 kg/m2) were studied in a crossover design comparing three conditions: no exercise, postprandial and post-absorptive exercise (at approximately 60% of the individual VO2max for 45 minutes). Substrate use was evaluated by indirect calorimetry during exercise. Venous blood samples were taken at regular (30- to 60-minute) intervals throughout the day, and glucose, insulin, and triglyceride concentrations were determined.
Results: During exercise, a higher fat oxidation rate was observed in the post-absorptive than the postprandial state. The glycemic response to a standardized high-carbohydrate breakfast was lower when exercising after breakfast than when exercising before breakfast. There was no effect of either exercise mode on glucose and insulin response to lunch and supper.
Discussion: Post-absorptive exercise has the advantage of promoting fat use, whereas postprandial exercise can attenuate the glycemic response to breakfast. Neither exercise mode acutely induces improved glucoregulation later during the day. The impact of meal timing on the effects of regular exercise training on glycemic control in this population remains to be studied.