You aren't supposed to eat something for a period of time if they are doing bloodwork. They want to get your fasted state blood sugar levels. Just call the doctors office and they will tell you. If you are not getting blood work on your physical, then don't worry about it.
If it is in the morning, first thing, just don't eat anything before you go. If it is later in the day, just eat a couple of scrambled eggs to tide you over.