Grapes may help you from developing autoimmune diabetes.

Preliminary animal studies show that compounds found in grapes may reduce the risk for autoimmune diabetes in humans.

Type I juvenile diabetes mellitus occurs when T lymphocytes and monocytes (immune cells) attack the islets of Langerhans of the pancreas, resulting in inflammation and progressive destruction of the insulin-producing ß cells. Researchers in this study hypothesized that feeding nonobese diabetic (NOD) mice diets rich in polyphenols or vitamin A, both known modulators of immune function, would decrease the autoimmune inflammatory process associated with type I diabetes.

After being treated with either 1% freeze-dried grape powder or 250 IU vitamin A, the incidence of diabetes was reduced to 33%  and 25% in mice receiving 1% dietary grape powder and vitamin A, respectively. Mice receiving both grape powder and vitamin had lower TNF- production (immune cells) than the control mice treated with nothing. There was also a significant reduction in the severity of insulitis in the mice receiving grape powder and vitamin A compared with the control group. This study suggests that diets rich in polyphenols or vitamin A have protective effects against autoimmune inflammatory attack of the islet ß cells and have the potential to reduce the onset and pathogenesis of autoimmune diabetes.1

References:
1. American Society for Nutrition J. Nutr. 137:1216-1221, May 2007.