Some studies have suggested that the quality of the food fed to a cat determines the cat's risk for diabetes. For example, it was previously thought that dry foods, which are higher in starch and carbohydrates, lead to an increased risk of diabetes as compared to higher protein-based wet cat foods. However, more recent studies suggest that what type of food being fed is not as important as quantity of food. Overweight cats are at highest risk for diabetes, and that cats that eat dry food have a higher incidence of obesity than those that eat only canned or wet food. So, the best way to prevent diabetes in your cat is to feed your kitty the proper amount of food to maintain ideal body weight.
If you have any concern that your cat could be a diabetic (ie, the main symptoms are increased thirst and urination), see your veterinarian. Diabetes in cats is easily diagnosed with a simple blood and urine tests.