Vets will tell you that being spayed does not make a dog gain weight. Just like a person, only if you stop exercising will you gain. None of the dogs I've ever had(and they've all be spayed/neutered, have gained anymore weight after being fixed. That's another myth actually.
Myth 1: If I get my pet spayed or neutered, he or she will get fat and lazy.
As if most dogs and cats didn't already lie around
the house all day anyway...
In any case, this myth about spaying and neutering pets might be true if you overfeed your pet and don't exercise him enough, but that's hardly the fault of the procedure, now is it?