"Don't orcs eat, and don't they drink? Or do they just live on foul air and poison?"
"No, they eat and drink, Sam. The Shadow that bred them can only mock, it cannot make: not real new things of its own. I don't think it gave life to the orcs, it only ruined them and twisted them; and if they are to live at all, they have to live like other living creatures. Foul waters and foul meats they'll take, if they can get no better, but not poison."
 

-Frodo Baggins to Samwise Gamgee