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Studies Question Health Benefit of Post-Exercise Meals

01.09.2008
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.

Barry S. Braun, associate professor of kinesiology and director of the Energy Metabolism laboratory at UMass Amherst, says most people who exercise aren’t 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.

Braun says for ordinary people who are using physical activity to improve their health, exercise is a medicine. Each “dose” of exercise gives benefits but 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,” Braun says.

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. In the first study, published in the Journal of Applied Physiology, Steve Black showed that walking on a treadmill for one hour daily, which burned 500 calories, increased the effectiveness of insulin to clear blood sugar by 40 percent. But when the 500 calories burned was replaced by feeding the participants a high-carbohydrate drink following exercise, the positive effect disappeared entirely, along with improvements in several other key health markers like blood lipids and inflammatory proteins.

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, 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, published in the Journal of Applied Physiology, Nutrition and Metabolism, 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.

Brooke Stephens-Hasson conducted a study, also published in the Journal of Applied Physiology, Nutrition and Metabolism, in which she changed the timing of when the meal was given while keeping the total calories and carbohydrate content of each meal constant. She compared identical meals given before, immediately after, or three hours after 75 minutes of moderately intense bicycling. Once again, the effectiveness of insulin to clear blood sugar was better after any of the exercise conditions compared to a no-exercise condition. 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.

Barry S. Braun | Newswise Science News
Further information:
http://www.umass.edu

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