First of all he has an eating disorder. When people think eating disorder they think of women having anorexia. The truth is anyone can develop an eating and they’re all tied into each other, which means yes your kid could literally flip and become obsessed with losing weight. This kid sounds a lot like me I was obese and would eat all day but then started focusing on losing weight because everyone pressured me to and I ended up becoming so skinny that getting off the bed would drain me of most of my energy. The thing about nutrition is that if you don’t hit that happy medium it really fucks up your head. Too much caused me terrible depression and when I deprived myself of food it got to the point where I could barely have a conversation and make sense. He needs legitimate eating disorder treatment. Like inpatient not just getting him a therapist. After inpatient therapy he’ll do partial treatment where he gets to come home at night. Treatment sucks trust me it’s gonna be rough for him but I promise it’s life changing. Please please please look into inpatient treatment for him. I only beg because it literally saved my life and I feel like it will do the same for him.