The main things a diabetic has to watch out for are fat, salt and sugar. If you watch these and the portions, you should not have too many problems. Don't go out and eat a whole lot of fruit and muesli in order to be "Healthy" because they are full of sugar.
There are lots of books on low GI foods to eat, so they are good to read and he should stay off the rice and potatoes as there are only a couple of varieties of each that are low GI. It is best to be strict with yourself because it will slow down the side - effects of the disease.
Dr Jennie Brand Miller and Co. has written the best book, in my opinion, on low GI. I have her books and recommend them.
http://books.google.com/books?id=cUz...page&q&f=false