I have tried virtually all the mainstream IF protocols including 16:8, 20:4 and even a bit of OMAD. All of them work. Are they sustainable? Maybe for some people. But in general I think they should not be used long-term as, yes, there is a significant chance of it permanently lowering your BMR/metabolism. Fasting IS a stressor, and increases cortisol. People need to do more research before going all-in on this stuff.
I have tried virtually all the mainstream IF protocols including 16:8, 20:4 and even a bit of OMAD. All of them work. Are they sustainable? Maybe for some people. But in general I think they should not be used long-term as, yes, there is a significant chance of it permanently lowering your BMR/metabolism. Fasting IS a stressor, and increases cortisol. People need to do more research before going all-in on this stuff.