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Protein and exercise: what does science say?

Athletes, coaches and scientists have recognized for decades that training and nutrition are highly interrelated in improving performance.

Nutrition intake right after exercising may benefit the athlete in that it aids the synthesis of muscle protein and the replenishment of muscle glycogen.

Similar to the effect seen after resistance exercise, consuming protein with carbohydrate during recovery from endurance exercise promotes muscle repair. This may be due to a direct effect of amino acids on signaling pathways that control muscle protein synthesis.

A more controversial issue is whether consuming protein with carbohydrate enhances muscle glycogen resynthesis during the first several hours of recovery from prolonged exercise.

Most evidence suggests that ingesting a high amount of carbohydrate at frequent intervals negates the benefits of added protein. However, if an athlete does not eat enough carbohydrate during recovery, then consuming protein with carbohydrate may augment glycogen synthesis.

Thus, similar to the effect on endurance capacity, the beneficial effect of ingesting protein with carbohydrate on glycogen storage may be due to higher nutrient intake per se rather than any unique physiological mechanism.

A key issue for some athletes is whether consuming protein with carbohydrate during recovery improves subsequent endurance performance. One study reported that ingesting a carbohydrate-protein drink during recovery from glycogen-depleting exercise--activity lasting more than 90 minutes--markedly improved time to exhaustion during a subsequent exercise bout, as compared to a sports drink.

However, the carbohydrate-protein drink provided about three times as many calories as the sports drink, and thus the improved endurance capacity could have been due to the higher energy intake.

Another study that did not match energy intake compared chocolate milk, a diluted carbohydrate sports drink and a drink matched to chocolate milk in terms of protein and carbohydrate content.

Endurance capacity was improved with chocolate milk and the sports drink compared to the third beverage, even though the latter provided carbohydrate and protein equivalent to chocolate milk and more carbohydrate and energy than the sports drink. The mechanisms that might explain the rather surprising findings are unclear.

Studies that have compared a carbohydrate-protein drink with a carbohydrate drink that provided the same amount of energy showed no difference in a subsequent 5-kilometer running time trial or a timed run to exhaustion.

So there is no compelling evidence that suggests consuming protein with carbohydrate during recovery has a direct effect on subsequent exercise performance.

Nonetheless; given that protein has been shown to promote muscle recovery after strenuous exercise, it seems prudent for athletes to consume protein with carbohydrate as part of their recovery strategy.

These conclusions can be drawn:

* Some studies have suggested that consuming protein with carbohydrate during exercise improves endurance performance, while other studies have reported no benefits. There is no established mechanism by which protein intake during exercise should improve performance.

* Recent evidence indicates that when enough carbohydrate is consumed during exercise, adding protein provides no performance benefit and does not enhance muscle glycogen synthesis after exercise.

* Consuming a small amount--10 to 20 grams--of high-quality protein after exercise promotes muscle protein synthesis compared to carbohydrate alone and may enhance long-term training.
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Title Annotation:HEALTH
Author:Gibala, Martin J.
Geographic Code:1USA
Date:Nov 1, 2012
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