Dietitian Jack Norris has published an excellent overview of research on vegan diets and diabetes on

Please note Jack’s comments about fat in his discussion of the findings. I agree with him that adopting a very low fat diet over the long term may not be advisable. I’m also not convinced that severe fat restriction is helpful in managing diabetes; other research suggests that replacing carbohydrate in the diet with monounsaturated fats improves diabetic control. Higher fat diets may also improve blood cholesterol (as long as the diet is still very low in saturated fat).

Finally, weight loss is among the most powerful ways of improving diabetes control, so it’s very hard to draw any conclusions about impact of various dietary factors when the subjects lose weight. With that said—it makes sense that vegan diets would be a good choice for people with diabetes since they tend to have a lower glycemic index and are high in fiber. And vegans (on average—but certainly not always!) have a lower body mass index.

Here is a link to Jack’s blog which links to the article.