Help for a friend

I have a friend who was recently denied for his surgery, and he needs it badly. he has diabetes and high blood pressure problems,,and is currently off work due to those things. Does anyone have a sample of an appeal letter we could use as a model for us to write one? I had my surgery with no hitches,,was approved in 6 hours, but I had a lot of diet documentation too, he does not. Any help would be appreciated. The insurance company told him 6 months of doctor supervised diet,,and he is doing that, is in his third month right now. But what else can we do? thanks everyone!