"Set point" was one of the first disagreements I had with gNads, and resulted in a threatened 'iggy'. She maintained that the body 'knows' what it wants to weigh, and adjusting what and how much one eats and exercises will not affect the weight because of that 'body knowledge'.
Increase exercise, reduce caloric intake - if the body has not attained the 'set point', it won't matter.
If the bodies of the starving people of the Sudan region had 'set points' of 180 lbs, would they look healthy despite the lack of food? This was a question she would not answer.
I think she uses the 'set point' argument to justify being large.