If the game will have difficulty options when released, that would be one way to restrict it. Make eating food in combat available on Easy and locked out of combat on Normal and Hard.
I like that better than the "just don't do it if you don't like it" approach, or even a settings in an Options menu. You're choosing what kind of experience you want with the difficulty settings, and it avoids looking like dumb game design if you're a more hardcore player.
