I can't speak for everyone, but my body definitly has a set point. I'm 5'6" and that set point seems to be around 125ish. Not ripped, but enough that you can see muscle definition. I've been cover model ripped as hell before, and my body definitly didn't like it, and it required a super strict adherence to primal ontop of being a gym rat to accomplish it. Was funny, everyone always told me how healthy I was, when in reality I am pretty sure I am healthier now with a little more meat on my bones. That being said, I have also been around 140 before, and my body definitly didn't like that either, atleast in terms of how I felt, but it was plenty happy staying at that point.
“To insure good health: eat lightly, breathe deeply, live moderately, cultivate cheerfulness, and maintain an interest in life.” - William Londen