The three studies, published by kinesiology researchers at the University of Massachusetts Amherst, suggest that, unless you are a competitive athlete, consuming sports drinks or high-carbohydrate foods such as energy bars right after exercising may negate the health benefits that physical exercise creates.
According to Barry S. Braun, associate professor of kinesiology and director of the Energy Metabolism laboratory at UMass Amherst, most people who exercise are competitive athletes.
They exercise to help their overall health, seeking to manage their weight and reduce risk for diabetes, heart disease or other health problems.
For them, the potent benefits of exercise are quickly reversed by consuming high-carbohydrate foods such as sports drinks and energy bars after workouts.
But, for ordinary people who are using physical activity to improve their health, exercise is a medicine. Though each 'dose' of exercise gives benefits, the effects are lost in one to two days.
Like other medications, exercise also has interactions with food.
Recommendations for athletes seeking to optimize their performance may be precisely the wrong advice for people using exercise to improve their health.
"The latter might be wiser to avoid sports drinks and energy bars during, and for one to three hours following, exercise to maximize the positive effects of each exercise dose," said Braun.
In three recently published studies, graduate students under Braun's direction looked at how the total calories, the carbohydrate content, and the timing of post-exercise meals influence metabolic health.
To understand whether the negative effects of the post-exercise meal were due to the total calories or to the carbohydrate content of the meal, Braun's student Kaila Holtz tested two different meals given immediately after 75 minutes of moderately intense bicycle exercise.
The meals contained exactly the same amount of calories but one was high in carbohydrates and the other was very low in carbohydrates.
Her results showed that the effectiveness of insulin to clear sugar from the blood was greater after either exercise/meal combination compared to participants who did not exercise.
The effects were larger, however, when the meal was low in carbohydrates.
These results suggest that, when the post-exercise meal is low in carbohydrates, more of the metabolic benefits of exercise are retained.
Although there were a few subtle differences, the results were similar among all three exercise/meal combinations, suggesting that timing of the meals was not an important consideration.