Like, I just was thinking about how lots of pet species will just eat as much food as you give them to the point of making themselves sick, and keeping them at a healthy weight requires not giving them access to too much food. Obviously some humans have problems with this, but imagine how bad things would be if everyone were basically psychologically incapable of not eating food when we had access to it even when we’d had enough, given our dramatically higher access to food due to agriculture.
This is just on the top of my head, but since obesity is one of the leading causes of death, coupled with the stigma of getting into relationships with obese people, in the far future the genes somehow responsible for obesity would be gone. Those who would survive and pass on their genes are the normal or at most, overweight ones.
Natural selection like that only occurs if you die before you get a chance to reproduce, a lot of the diseases affecting the obese kill you a bit later than that. And of course it’s not just a genetic thing either.
But to be fair, obesity does affect your chances of finding a mate.
Obesity is also linked to an increased chance of infertility in both men and women.