From what I've read some people have success with this and others don't. I recently read a post on "Earth Clinic" from a husband commenting on how successful berberine had been in treating his wife's diabetes.
It goes under several names: bitter melon, bitter gourd, karela, and, of course, berberine, and can be purchased in its natural state from Asian stores. Without checking, I'm not too sure whether it's a fruit or a vegetable. A while ago I did purchase some and cooked it but found it extremely bitter, and because it was so bitter I didn't pursue the experiment as to whether it worked or not. So I think the easy option would be to take it in tablet/capsule form.
It's worth a try!