Diabetes mellitis has, unfortunately, become a common diagnosis in veterinary medicine. Pets are being fed diets that are inappropriate, laden with carbohydrates that break down into sugars, causing secondary problems like obesity and diabetes. Cats are carnivores and should not be fed dry kibble, as the carbohydrate content is very high in kibble food (minimum 45 to 50% carbs). Dogs don't fare much better, but their metabolism is a bit better suited.
Once a pet is diagnosed with diabetes, it becomes imperative to feed a more species-appropriate diet in order to regulate the blood sugar fluctuations. Here is an excerpt from my book From Needles to Natural: Learning Holistic Pet Healing:
"Diet plays an extremely important role in regulating and maintaining diabetic pets. Without controlling the diet, you will not control the diabetes. Diets high in carbohydrates will cause increased insulin requirements and will make control more difficult. Diets deficient in moisture will add to the problems of increased thirst and urination...Medications and supplements can interfere with insulin and sugar metabolism, making it difficult to get the pet regulated. Be sure to tell your veterinarian about all supplements you are giving...If you are having a difficult time achieving diabetic regulation, have your pet checked for other endocrine diseases, such as Cushing's disease or hyporthyroidism. If concurrent disease is left untreated, diabetes can be hard to manage."
I have had great success getting diabetic patients regulated and maintained with low doses of insulin by feeding a meat-based diet suitable for dogs and cats. My pets eat this diet, which helps maintain proper weight and metabolism.