MYTH: A spayed or neutered cat will invariably gain weight.
FACT: Like most animals, including humans, cats get fat either by eating too much, or by not exercising enough, or by a combination of both. These sterilizing operations are often performed on cats at an age when their metabolic rates have slowed down, meaning they need less food than younger animals. If the cat continues to eat the amount of food it has been used to before the operation, it may gain weight. You can help a spayed or neutered cat to stay fit by making sure that it does not overeat and that it gets plenty of exercise.
You should see an indentation just behind your cat's ribs when you look at it from above. If you have difficulty feeling its ribs and it is difficult to make out this indentation then your cat is most likely overweight.
My tabby is quite tubby so I have to watch what she eats. In a multi-cat household that is not always easy. I have changed their treats from Temptations to Pure-Bites because Pure-Bites Chicken Breast treats have one calorie per treat. They love em!