I would have quit that vet too. That's just cruel. Calories were not the dogs problem, it sounds like the thyroid and diabetes were. I had a dog that had kidney failure, she lived to be 17 but it was still hard to lose her. The last six months to a year I let her eat whatever the heck she wanted. The vet kept saying she needed low protein but heck, I was going for Quality not quantity at that point.