Imagine taking a long run on a Florida trail in the middle of the summer. Up ahead you see a taco stand selling steak tacos. The thought of ingesting protein when it's muggy outside isn't pleasant, but you absolutely have to have protein for fuel. Without it, your body will begin to cannibalize itself -- that is, it will turn to muscle as a source of energy [source: Hammer Nutrition].
Fortunately, you don't have to carry a steak or kidney beans in your pockets, and you don't have to stop at a taco stand. Protein supplements come in a variety of forms -- including refreshing liquids.