This has happened to cats I have owned many, many times. I recently took my long haired cat to get a lion cut and they gave him a sedative in order to do it so when he came home 2 of the cats hated him and kept trying to attack him and one had no problem with him at all. It took about a week...
It is just genetics. It isn't fat or anything to worry about. It isn't about spaying or neutering. Two of my cats have it and two don't. One that does is female and the other male. I have read that it is for times of plenty so they can gorge themselves when there is food so that they can...