Did the vet take him off the insulin?

I'd try a second opinion, taking the results of the lab tests from the first vet.

Without some sort of insulin, all the best food in the world will do no good.

http://www.petdiabetes.org/faq.htm#types

http://www.petdiabetes.org/faq.htm

http://sugarcats.blogspot.com/2006/0...at-feline.html

smokey the elder has lots of experience with diabetic kitties, so hopefully that point of view will be here shortly.