I had a diabetic dog. She did have to get insulin injections twice a day, but there were many dietary issues involved, also.

I eliminated dry kibble. Most contain grains and also lack moisture. Your cat will need as much moisture/water as you can get it to drink. You may think you should hold back water because of all the peeing, but that is a bad thing to do. They will pee a lot anyway if their blood Sugar is high, because that is how the body tries to flush it from the system. By holding back water when they will pee a lot anyways, this will cause major dehydration.

Minimize/eliminate salt/sodium products. This will cause blood Sugar levels to skyrocket.

Also, check ingredients in all food and treats for sweeteners. I was shocked at how mnay treats, cookies, etc. contained some form of sweetener -- sugar, honey, molasses, maple syrup, fructose, etc.

I'm not sure if glucosamine is a supplement given to cats for joints, but I learned the hard way (through my own research and not from the vet - disappointed he didn't know to tell me) that glucosamine can raise blood Sugar levels.

I didn't feed my dog any grains at all. Really the only carbohydrates she got were lima beans occasionally (her favorite food --- weird, I know). I fed her lean beef or chicken and lots of vegetables. Some people believe they still need grains/carbs, others feel they do not. It's your call, but carbs can turn to sugar easily.

Oh, you may also want to look into some different supplements geared towards kidney/diabetes. Vetri-Science has a line of products. I give my current dog one called Renal Essentials. She had high bun levels, but they are in the normal range with these supplements.

You may also try the Only Natural Pet website. They contain a lot of different natural products. Pet Remedies also has homeopathic treatments for many different ailments.

I would still recommend a vet, because not controlling the blood Sugar levels can cause fast forming cataracts / blindness, kidney problems, and much else. However, supplementing with natural products is a good idea. Chromium is recommended for people with diabetes, but I'm not sure about cats.

I could be wrong, but I'm thinking that it is recommended that dogs with diabetes/kidney issues should be given fish oil made from the whole body.