Food Journals?

My doctor said to keep a food journal so that I know what raises my sugar and what keeps it steady. But he failed to tell me what to write down. Do I write just the food that I am eating? Or be very specific (wheat bread, turkey, cheese, lettuce, etc) Do I write the calories, fiber, carbs down as well?

if you can get the specifics that would be great in the beginning to maybe identifying what causes a spike or low maybe so you can get idea how differnt ingredents or portions affect you but if that is too much go w/ the general info