Milk.
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Milk: The New Sports Drink? A Review | BodyRecomposition - The Home of Lyle McDonald and
Milk as an Effective Post-Exercise Rehydration Drink | BodyRecomposition - The Home of Lyle McDonald
I currently use 8oz's of skim milk, and 8oz's of water PWO. Trying to get leaner right now. I would switch to 2% or whole milk if trying to gain mass.
Bottom line is that whey/casien combo's PWO instead of just whey has been shown to be superior.