Diabetes is a disease in which the body either does not produce enough of the hormone insulin, or produces enough but does not use it properly. When either of those things happens the body does not use carbohydrates (sugars) properly, and that causes blood sugar levels to rise.
In humans you may have heard the terms Type 1, Type 2, insulin-dependent, or non-insulin-dependent to describe the kind of diabetes the person has.
Type 1 means the same thing as insulin-dependent (technically that is not entirely accurate, but the difference is irrelevant for us right now). A person who is described as Type 1 diabetic or insulin-dependent diabetic is one who no longer produces enough insulin on their own and must take insulin injections to survive.
Type 2 means the same thing as non-insulin-dependent (again, not technically true, but good enough for us right now). A person who is described as Type 2 diabetic or non-insulin-dependent diabetic is one who produces enough insulin, but does not use it properly. These are the people for whom “diet and exercise” can often cure their diabetes. Usually they will take insulin when they are first diagnosed, and may take insulin periodically, but they may not be required to take insulin forever.
Why did I waste all that time talking about humans when this is a site about cats? I am glad you asked!
Overwhelmingly, when cats are diagnosed with diabetes, they are diagnosed as having the Type 2 kind. And that is great news for kitties and parents, because it means that there is an possibility that the diabetes can be reversed. Dogs are not quite that lucky, they are typically Type 1 diabetics, so if you have a dog, do not let them read this page. I do not want them to feel sad.
Disease Information Sites
http://www.felinediabetes.com/ is probably the best site around for understanding and managing diabetes in your cat.
If your cat happens to also have Chronic Kidney Disease, be sure to check out the resources listed on that page. There is information in the linked website about managing both diseases together, and there are members in the support group for that site who have cats with both diseases.
If your cat has cancer or an autoimmune disease that requires the use of steroids, such as prednisolone, you will want to make sure you understand each condition, and hopefully you will have access to support groups for each condition. Steroids will raise blood sugar levels, and diabetic cats in remission can relapse into full blown diabetes.
The Feline Diabetes website has their own support group as well. This group is run through an online message board and can be found at http://www.felinediabetes.com/FDMB/