Ever wonder why athletes carbo-load? Carbohydrates are the first source your body goes to when it needs fuel to burn—whether it’s a marathon or a spin class. You want to nosh on carbs an hour or two before you work out to allow your body to digest a bit, but still have access to that fuel. Protein may be packed with energy, but it’s harder to digest and therefore more likely to upset your stomach during a workout. Same goes for fat. Pick up a banana or Luna bar to prepare for a moderate workout. Snack on both before a major sweat sesh.