Adipose tissue retains an epigenetic memory of obesity after weight loss

As this article shows, there are incredibly complex feedback mechanisms around weight and metabolism, but thermodynamics are still fundamentally a thing.

After he died last year, I ran across this engineering and accounting approach to weight maintenance and loss written up by John Walker (one of the Autodesk founders). It worked very well for him and changed the way I thought about weight and eating. It is interesting reading because he is "one of us"

    https://www.fourmilab.ch/hackdiet/

Basically, he uses a first level approximation of the body as a control system with a feedback loop, and tries to pin down some techniques to bring the system to a known good state (target weight) and manage that loop for long term stability.