ANYTHING else is just hearsay.
My MIL has fasted regularly for decades. She’s 90, walks everywhere, takes no medicines, and still has a sharp mind. (She does have a bit of arthritis in her hands.) She also takes a host of vitamins and eats small meals.
One problem with the correlational study may be that people who fast regularly are more health conscious to begin with and probably exercise more, eat more healtful meals, etc.