Unfortunately, we live with this. Over kt's weekend pass, she ate every fruit snack in the house & proceeded on to a box of wheat thins. I asked her about it - "my midnight snack, mom".
I have found that you cannot win any battle that goes into or comes out of a difficult children mouth. However you lead the war; I generally have a bowl of popcorn out on the counter along with grapes & veggies when kt is home.
husband & I have cleared out all the "junk" food. There isn't much here anyway but with kt coming home this weekend for good we wanted all "garbage" out of the house.
I have a snack drawer that kt is free to chose snacks from at snack time. During other times she can munch on the popcorn & whatever I've put out for her on the island.
I also keep lots of sugar free gum in the house - kt has learned to chew gum versus eating nonstop.
I allow candy, fruit pops, etc, in limited amounts. I bake my own cookies & keep them in the freezer - take out a half dozen at a time.
This may sound annoying but it's become a way of life here. Reactive Attachment Disorder (RAD) children typically have huge food issues, add in BiPolar (BP) & all bets are off.