As to the basic statement that animals automatically keep weight “correct”, total horse pucky. Get off yer butt (fat or otherwise) and go observe.
Predators gorge themselves right after a kill. Then, lay about until they digest. And, then they go out to hunt again. Can they hunt with their bellies dragging? ‘Ell no.
Same with herbivores. They gorge themselves. But, but, if too fat they get culled by the predators.
There is no naturally “healthy” system working here, except “eat or be eaten”.
Humans and their companions/food animals have the ability to insulate themselves from this cycle. There is nothing intrinsic going on.
It is simply eating too much. Close yer pie hole for a bit and your weight will come down. Don’t and you waddle about. There is no intrinsically healthy food. It is calories.