Quotewell the past films show that they didn't and didn't need to. No evidence of food storage being raided in the colony complex in Aliens, nor were any chestbursted bodies eaten after death. (Notice Alien:Resurrection and Aliens)
I agree when people say they shouldn't have to eat. My personal preference.
But Alien 3 at least first brought up the idea, and if you think that it wasn't 'eating' whether for aditional benefits or whatever, then maybe the scenes in this movie will be the same way and people can interpret it however they want.
On a side note, I think it's an inevitability that as more movies are created with aliens and preds in them, the more mysteries about them are solved because every movie does that to some degree. With each movie made, there are less mysteries. Now I don't like that because one, it ruins them sometimes when revealing details, and two sometimes there are parts about them added I don't like. but I guess it's the downside to seeing them on screen again.
And yes, canon is a seperate issue.