I wrote a three-part series of articles on "50 Years of Running" [1], and the issue of motivation is specifically addressed, since how else would you keep up something for 50 years?
It's not at all about eating, and I'm honestly not sure it'll help you, but the tag in the first article is:
If you can't find time to exercise, you'll have to find time to be sick.
This is one of the least helpful advice one can give...
We all know that "if you can't find time to exercise, you'll have to find time to be sick", but in practice we're either wired to overfocus on short term rewards, or we don't really have any connection or emapthy with our future self ("let that bastard rot and die if he ain't got a currage to put a bullet in his head when it gets too nasty") etc. etc.
It's easy to talk from the high horse when you've been blessed with a mind not made up of pieces that are always fighting with each other or always prone to focus on other more stuff more important than your health (yes, there are more important problems in the world than you and your health!)...
It's not at all about eating, and I'm honestly not sure it'll help you, but the tag in the first article is:
If you can't find time to exercise, you'll have to find time to be sick.
[1] https://albertcory50.substack.com