Apples. In a Finnish study, men who ate the most apples and other foods high in quercetin had 20 percent less diabetes and heart disease deaths.
Generally, if you are at risk of diabetes it's important to eat plenty of fresh fruit and vegetables, get enough fibre and of course be very careful about fat, sugar and too many carbohydrates. Your doctor may well be able to give you a diet sheet, but in the meantime, the diabetes information website gives a clear overview of diet, exercise and other important points.
I have heard great things about cinnamon keeping blood sugar in check . I have researched it myself as I have no reason to but I have heard it a lot on TV, it may be worth your time to ask your doctor and research it .