Good point to bring up. Being overweight can severely shorten our pet's lives. It is more important than just the way they look -- it is a critical health factor to their heart, bones, and joints! I used to worry that my pups were too skinny but the vet said they were "lean" which is perfect for their health.
My Ben gained a pound (1 pound on a yorkie can be a lot!) after he was neutered & had also been sneaking puppy food in addition to his own. I think he had a jealousy factor going with Annie, our new puppy & wanted to eat all of her food! I actually noticed in pictures first. When we are just holding & hugging every day, we don't notice the very gradual addition of a pound or so. But in his pic, Ben definately showed me he needed some smart weight reduction. I thought it about it and not only was Ben getting additional calories in the form of his stolen puppy food, but he was also not getting as many walks as usual because Annie has not taken to the leash quite as well as I would like. Realizing I had neglected Ben's needs a little, I made a commitment to fix this!
I concentrated on two main things -- adding exercise and a switching to a different food. I switched all of my pups to the same All Life Stage food,
Solid Gold Just a Wee Bit. It has proved to be a great food! Ben can actually continue to eat the same quantity that he was, but this is better for him & not as high in calories. It is a low residue food too, meaning little compact, tootsie roll poops.

We are on an "all win" plan! He has lost most of the extra weight, still a little stockier than he had been for years, but at least not an unhealthy weight. This is something I'll have to stay on top of. Once fat cells are formed, they are always there, just waiting for a chance to plump up again. I want my Ben around for a very long time & do not want him to have to suffer bone & joint problems as he ages. So -- healthy weight it is!