If you push the issue and the kid is not interested it will only backfire. try to keep the junk in the house to minimal and/or get the “healthier” kind of junk. incoursge fruit and vegtables but DON’T make it a major issue otherwise it will become an emotional issue as well and the kid not only wont lose weight but a now have to battle emotional issues as well.
I took this approach with my daughter and recently she started putting in an effort and lost 6 kilo!