Hi Ellyn,
I see you just joined FDMB on Tuesday. Welcome to the group! I remember how overwhelming it was when I first got my cat's diagnosis and joined FDMB. There is so much to learn about feline diabetes, and it's easy to become overwhelmed with information. Take a deep breath. You can do this, and the amazing people here can help you.
My first vet, unfortunately, wasn't very knowledgeable about feline diabetes. He prescribed Hill's w/d for my cat, which I later found out was not much better than the Meow Mix I had been feeding her. Both were way too high in carbs for a diabetic kitty. My vet also didn't advocate home testing, but I'm really glad I did learn to test her at home - even though I was absolutely terrified to do so in the beginning. One day, Jersey dropped down to a glucose reading of 58 just four hours after her morning shot. At that time, we were using Humulin-N and feeding her the Hill's diet. (Just in case you may not know, we consider a reading of under 50 on a human meter to be too low. In other words, Jersey was close to going too low that morning.)
I would agree with some of the previous comments not to change foods until you are able to test your kitty's glucose. We definitely want to make sure your boy is safe, and switching to a low-carb food can cause insulin needs to decrease dramatically.
Back to the original question you raised,
here's a link on feline nutrition that you might find helpful.
Hang in there!
Shelly