A university study says that aerobic exercise, a known means of increasing insulin sensitivity, is most effective if the meals following it are low in carbohydrates. The study also revealed that consuming a low-calorie meal after exercising does not increase insulin sensitivity any better than eating a low-carb meal after a workout. In addition, it found that the beneficial effects of exercise are immediate and do not build up over time or last very long. Improvements in metabolism, including insulin sensitivity and lowered blood pressure, occur directly as a result of the latest exercise session, but taper off within hours or days. There is no “storing up” the benefits of exercise.
The study, which appears in the online edition of the Journal of Applied Physiology, was conducted by the University of Michigan. It looked at the effects of post-exercise diet on nine sedentary men, all healthy and in their late 20s. The men, who fasted beforehand, participated in four different study sessions, each lasting almost 30 hours.
The sessions differed in terms of what the men ate after exercising (or not exercising) on a treadmill and stationary bicycle:
- In a control session, the men did not exercise and ate meals that matched their daily calorie expenditure (approximately 12 calories per pound of weight).
- In another session, the men did 90 minutes of moderate exercise, followed by a meal that matched the calories they had just expended. The meal had balanced amounts of protein, fat, and carbohydrates.
- In a third session, the men exercised at moderate intensity for 90 minutes, then ate a meal with enough calories to match their energy expenditure, but with relatively low carbohydrate content. In this case, the amount of carbohydrate was 200 grams, less than half the carbs in the balanced meal.
- In a fourth session, the men exercised for 90 minutes at moderate intensity, then ate a low-calorie meal (about one-third fewer calories than the other two meals) that did not have enough calories to match what they had expended in exercise. This meal had a relatively high carbohydrate content.
The participants experienced increased insulin sensitivity after each of the three exercise sessions. However, the low-carb meals produced “significantly more” insulin sensitivity. That finding, said the researchers, indicates that even without dieting or losing weight, sedentary people who exercise and then eat a low-carb meal can gain an immediate metabolic benefit.
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