Oh boy, Cereal can be quite difficult for a diabetic. To answer your question, you should be paying close attention to the number of carbs, in total, in your cereal. Cereals like bran have a higher fiber content, which may make your "net carbs" lower, because the fiber makes the carbs take longer to break down. I have had type 1 diabetes since age 14, and in general I try to stay away from cereal.