We learn to evaluate the body condition score of dogs and cats in Nutrition class, basically the quick and dirty way to decide if they're skinny, fat, or in-between. This is what a body condition score chart looks like :

So Tigger meets the following criteria:
Can't really feel his ribs.
Doesn't have a waist.
Has an abdominal fat pad.
I'm sorry, Tigger, but you are officially a fatty. We're gonna put you at a 6 or a 7. And we're putting you on a diet. Several bags of "Light cat food for fatties" / "Light cat food for fatties with annoying long hair that makes them vomit up hairballs that their owners have to clean up at the most inconvenient times" - await you.
