Back to the OP, the hunger and satiety signals are very complicated and only partially driven by the digestive track.

I'm a fatty. I've lost a lot of weight but my body knows I used to be fat and it wants to be fat again.

A very potent signal for hunger or fatigue is when your fat cells get small i.e. you've burnt a lot of fat, and your little fuel cells are feeling empty. Each shrunken fat cell sends out a chemical "feed me" signal. And they are very very persuasive.

And the kicker is that when you fill them up, they want to be maintained at full. But if they're full too long, or get too full (persistently increase body fat by a few percent(, it triggers mitosis and you now have two half full fat cells who are both shouting "Feed me"

To add insult to injury when you lose weight, you don't kill off fat cells, you just have a bunch of really hungry fat cells shouting for a cheeseburger.

The nice thing about the GLP1 drugs is that they quiet the shouting. So you just don't get the demonic urge to feet all your wilting fat cells.

The bad thing about it is that the shouting is still there, and as soon as you quit the drug, you can get overwhelmed and go back to overeating and your weight and percent body fat go right back up