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.

The problem with diets based only on calories is that they don't take satiety into account, nor health.

Calories is what makes you gain/lose weight, it's basic physics. Satiety is what makes you want to eat more/less. Nutrients are what is making you healthy.

Fiber and protein tends to make you feel full. Lack of them allow you to eat large amount of calories without feeling full. You need to keep track of micro and macro nutrient to stay healthy.