With chronic diseases I’d be looking at focussing on a diet based around whole or minimally processed food and reducing or eliminating ultra processed foods. I’d start with time restricted feeding or intermittent fasting, rather than longer fasts.
I’m a big fan of Tim Spector, and there are a many podcasts he’s done about the impacts he’s seen of fasting in his research, and he’s about to start a new wide scale research project into fasting, which I don’t think it’s too late to join.
I have a couple of chronic autoimmune issues that my doctors have said are permanent. I’ve been able to manage a few really well buy sticking to a vegan whole food diet. The worst one is noticeably better when I fast but comes back with eating. I’m working up to longer fasts to see it I can heal. I also developed a lot of weird allergies to foods. I suspect they are all related.
I haven’t really been able to narrow things down to specific food triggers. It may be I’m simply getting more nutrients eating vegan.
I’ve never had an ED and don’t know enough about it either way. You can look into FMD (Fast Mimicking Diet). Prolon is the big one but there’s a sub where people do their own versions.