I have 4 kittens which were ferals that I took in. I had all 4 spayed/neutered and one of the four, a female, has gained a ton of weight. The other three, two males and a female, have stayed thin. She doesn't seem to eat more than the others so I am concerned it may be something else. I would say the other kittens are around 3-5lbs while she is easily 8lbs or so. They are around 3 months now I think.