You should try bloodletting...I know they practiced this often back in the Crusader days.

Another safe method would be to run in a rubber suit on a treadmill next to a fire (make sure the rubber suit is far away from the fire of course).

The best method of all is too lock yourself in a room with four friends and have them beat the crap out of you until you can't stand. This burns countless calories as well as water weight loss. I know we practice this often at my High School's wrestling room.