In addition to triggering the muscle rebuilding process that follows the breakdown from training, a study published in the British Journal of Nutrition suggests that dairy proteins can help restore hydration by promoting the absorption of electrolytes. Compared to water, low-fat milk (2%) did a better job of restoring body water levels in dehydrated people.
This doesn't mean you should rely on your favorite protein shake to rehydrate after a long grueling session under stacks of heavy iron plates. Even a little dehydration can take something away from your physical performance. For more on the subject, check out yesterday's Breaking News story at OptimumNutrition.com which showed how hydration status can affect post-workout hunger hormones.