Both. Your body will need energy to burn to make your workout as effective as possible, a snack like a banana and a cup of yogurt, or a sandwich with wheat bread and peanut butter would be great. If you’re body has no fuel, it will take from stored protein or fat. What usually happens is your body ends up cannibalizing on it’s own muscle for energy. After your workout you’ll want to give the body protein for muscle recovery, if you’re planning on going right to bed soon after, you may not need as many carbohydrates.