i have a strategy that is counter to most of the suggestions in this thread. i was in a similar situation to OP's, not food related but i don't want to go into that much detail on a public forum.
the only thing that worked, after years of trying to change the behavior of another human being, was to give up and detach physically and emotionally. i stood in and picked up the slack with child rearing, cleaning the house and everything else that should have been shared. in a way it was positive because i'm much closer with my kid as a result.
detaching was the only way i could stay sane. continuing to care was making me literally crazy and sick. but when i made the decision to reduce contact, i began to make positive changes to my own routine and slowly gained my strength back. i changed my already pretty good diet to a stellar one. hit the gym, played more sports etc. basically only spoke to the other half for functional things like who's in charge of the kid and what obligations we have outside the home. it's important to note that this was strictly a strategy for my own mental health. i was going nuts.
the other half will see the positive changes and at first be mad, then jealous, then all other kinds of crazy but she will never change until SHE wants to and has the drive to do it. eventually she realized she wanted to be in a relationship again and made major changes. things are pretty much ok now, but not because i did anything to change her. she did it all herself while i was detached and mildly supportive.
bottom line: OP take care of yourself and let your wife live in peace or die in peace. forcing a change isn't going to work. she'll change when she hits bottom as she defines it, not as you define it.