Well...always remember...muscle weighs more than fat. My Zoey weighs 4.25 pounds (1.93 kg). Can you tell I have a handy converter program? I had to use it to figure out how much Fido weighs in pounds so I could understand.
Seriously...can you feel his ribs and backbone? He may not be fat at all...just a bodybuilding muscle man!
Can you post a picture? I'd love to see Mr. Fido.