What's more natural than fresh and dried fruit? David Nieman's recent research found that eating half a banana with water every 15 minutes rehydrated and powered expert cyclists just as well as a cup of Gatorade. "Bananas have the perfect, highly bio-available blend of glucose, fructose, and sucrose, as well as a ton of potassium and vitamin C," Nieman says. Plus, bananas are cheap and portable. For hour-long runs or rides, he suggests eating one banana before or immediately after for max benefits. Nieman also recommends popping raisins with water during exercise. They are potassium bombs and deliver the proper amount and balance of sugars.