Feline obesity

I had to take my cat to the ASPCA for a check-up and shots the other day on East 92nd Street -- and he almost broke the scale. He weighs 16.8 pounds! When you are a cat, you can't convert carbs to energy. It goes straight to blibble. No wonder I can not breath when my cat sits on my neck or chest at night. Not sure what to do. I suppose I could switch him to the very stinky canned food -- the stinkier the better, as far as he is concerned --- but he eats one smidgen and then I put the rest in the refrigerator. There, in the corner, with a plastic lid that barely fits, the cat food stinks up all the other food items. He is a great cat but his laziness is pervasive.