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Better Rehydrator

In the battle over what best replenishes your body, there’s a surprise ending. Though we’ve been told time and again by experts that all you need is water or a sports drink to replenish lost fluids, the reality is this: Both water and the traditional sports drinks are inadequate. In fact, your best bet is to remove part of your sports drink and replace it with some protein, and here’s the science to prove that beyond a reasonable doubt.

Recently, science nerds compared the effects of milk protein on rehydration after exercise in the heat. The drinks were identical in electrolytes and calories. The main difference was that one included milk protein.

Eight men lost 1.9 percent of their body mass, or weight, through intermittent exercise in the heat. Then they rehydrated 150 percent of their body mass loss with a solution of either 65 grams of carbohydrate per liter or 40 grams of carbohydrate plus 25 grams of milk per liter. Urine samples were collected before and after exercise and for four hours after rehydration. Total urine output after rehydration was greater for the carb-only group than the carb-and-protein group. Total fluid retention over the study was greater for those who got the carb-and-protein drink.

Thus carb plus protein rehydrated folks much better after dehydrating exercise. Even if the drinks are identical in calories, fat content and sodium and potassium counts, a carbohydrate-and-milk-protein solution is better retained than a carbohydrate solution. Gram for gram, milk protein is more effective at supporting fluid retention than carbohydrate.1 So add some protein.

There’s another reason for using the combination. Another study looked at the effects of acute milk-based carb-and-protein-supplementation timing on exercise-induced muscle damage. Four groups of eight healthy men drank a milk-based carb-and-protein solution before, immediately after or 24 hours after muscle-damaging exercise. They discovered that it’s better to have the milk-based drink after rather than before muscle-damaging exercise to lessen decreases in muscle performance and increases in active delayed-onset muscle soreness at 48 hours.2

Bottom line: You’re much better off with a sports drink that has protein as well as carbs in it. In fact, milk-based proteins such as whey isolate are a great way to spur gains in muscle mass when taken immediately postworkout—plus they are a much better choice for replenishing fluids. So choose carbs plus protein.

Editor’s note: Jose Antonio, Ph.D., is the CEO of the International Society of Sports Nutrition (; also check out his site


1 James, L.J., et al. (2010). Effect of milk protein addition to a carbohydrate-electrolyte rehydration solution ingested after exercise in the heat. Br J Nutr. 28:1-7.

2 Cockburn, E., et al. (2010). Effect of milk-based carbohydrate-protein supplement timing on the attenuation of exercise-induced muscle damage. Appl Physiol Nutr Metab. 35(3):270-277.

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