Check out the Random Jack Fact:
http://www.notrly.com/jackbauer/index.php
Jack Bauer's biological make-up is so advanced that he internally recycles his own human waste into nourishment. That's why Jack never eats or goes to the bathroom.
Many ask what happened to Beruz in season 4. To Jack Bauer the day is a game, and if you leave the designated area without the blessing of Jack you get erased from existence.
He never brushes his teeth, either.