Short answer - For an hour long workout, nothing. Workout in a fasted state. Wait at least 3 hours after your last food.
Longer answer - Lets take it back few years. To a time before storing food for long periods of time was an option. Without a constant fuel source, we hunted and gathered when hunger came a knocking.
What causes hunger? Science has labeled the hormone ghrelin as the culprit. When you haven’t consumed adequate calories, this hormone makes us feel hungry. This feeling causes us to act. Back in the day, this act took labor and work to satisfy.
No one knows for sure but finding food back then might have spent as many calories as a modern day CrossFit workout. So, if hunger caused us to “work out” back then, as the theory goes, we are genetically hard wired to work out on an empty stomach.
Its apparent we are rock stars when it comes to storing calories. For an hour long workout, for a well fed human, you have plenty of stored energy to crush the WOD!
Workout fasted my friends.