There is a hormone called leptin (I think). It exists in our “fat cells”. Once the fat cells get filled to a certain point, leptin is released. Leptin tells us that we’re full.
People who have lots of fat have developed lots of fat cells, more than people who are thin and who also have never had lots of fat. The fat cells never die, even after losing all the body fat.
Once someone who once had lots of fat loses all that fat, it takes more food to fill up the fat cells to release that leptin to tell us we’re full, because there are so many of them.
So, eating can be a delicate balance for people who have lost fat. It takes more than waiting for that fullness feeling from the leptin.