I'm absolutely not an expert here, but with our first diabetic kitty, weight loss was a huge issue too. He was a big boy prior to DX as well (23lbs), and lost about as much as Bubba, and all three vets that we saw at our regular practice, and when he landed at NCSU Veterinary Teaching Hospital for some unrelated issues and was reviewed by multiple vets and students, they all said to *just feed him*. Make it the best food for his diagnosis, assuming he is eating. And of course if he ever stops eating (which I am sure makes you laugh because that isn't even on your radar at this point if he is like my boy was!), then feed him whatever he will eat. Unless you are feeding something like straight boiled chicken...which might be a good option to supplement calories and bulk...then he is getting more carbs then he would have normally and you should just adapt insulin accordingly.
They were all worried that weight loss added another variable to the equation, he could become weaker, and it also adds stress to his little kitty life being on a continuous hunt for food.
I would love to hear other opinions, but I just wanted to share what my vets had said.
Best,
Sandi.