Foods high on the glycemic index can cause glucose levels to spike upward very fast, but eating low glycemic index foods do not prevent type 2 diabetes. High blood glucose levels are just an indicator of the presence of diabetes, not the root cause. The disease is caused by the body's resistance to insulin which allows the glucose (from foods eaten) into the blood and then into each of our cells to be used as fuel.

Additional Resources:

http://www.diabetesnet.com/diabetes_food_diet/glycemic_index.php

http://lpi.oregonstate.edu/infocenter/foods/grains/gigl.html