I do agree that it's more than what your body is used to, I think it's as much as what your lifestyle encourages.
Everyone knows that we tend to eat the same foods over and over, and we are much more creatures of habit than we admit to ourselves at times.
So, I think there is a point where it's subconsciously uncomfortable to go any lower with calories or higher with activity levels. To change those things, takes a REAL effort on our part and so it feels dramatic when we do it, and when we do it, it's harder to keep up long term.
IF we do keep it up, then that will become our go-to pattern and thereby establishing a new set point.

