Confirmed in two of the films and plenty of the comics, if you consider the games canon then that too. They eat meat.
The Runner was eating a prisoner in Alien 3, Ripley even said "I could have been lunch"
It became even more obvious in AVP-R when The Alien was snacking on that teen next to the pool.
Personally, I dont think they need to eat to survive, its probably just satisfying for them and helps their bodies heal faster if they are injured.