I did not know that yesterday!

Food is hard to come by in the wild, so rarely will an animal will have the opportunity to overfeed. Occasional access to extra nutrition generally results in a benefit to the next generation, by either the production of more young or a size advantage in the competition for mates.

Some wild animals, especially those that hibernate, put on additional weight in the fall that they can use for energy in the winter. They conserve that energy during the colder months by decreasing activity. The American black bear begins to prepare for hibernation in the summer, and can gain as much as 30 pounds per week. It then loses about half its total weight while wintering-over.

Usually when there's an imbalance between activity spent hunting or foraging and amount of food intake, humans are involved. Captive and domesticated animals can be more prone to a sedentary lifestyle, in which they don't need to expend much energy for their meals. Even animals closer to human populations might behave differently than those in the wilderness.