> Trying to diet didn't really cause any maintainable change.

That's not a surprise. Changing diet composition can in the short-run lead to lower caloric intake than what preceeded (e.g. SAD diet), but doesn't guarantee a sustained caloric deficit, which is why controlling for macros like fat or carbs eventually hits a wall. What are you going to do when there are no more carbs to cut? If you have a lot of excess to lose, you can't "intuitively" eat your way down to your target.

The fasts work similarly owing to deficit: a fasted day lowers the average caloric intake for the week (assuming you don't overcompensate other days). As with macros, here again, what are you going to do to increase deficit further? Fast for 48 hours? If with a fast your caloric intake isn't dropping further week-to-week, weight loss will stagnate.

Whichever approach, one of the pitfalls is steep deficit followed by metabolic adaptation i.e. crashing metabolism. This is why it's helpful to keep a small caloric deficit, and incrementally change your intake target. That is only reliably achieved by tracking calories.