For anyone suffering from diabetes, it's important to eat fiber-rich foods. This is especially true for patients of Type 2 diabetes.
But to answer the question of how fiber controls blood sugar, the simple answer to this is that it does not increase blood glucose levels. Since fiber is not broken down by the body, the fiber-rich food you eat does not impact blood glucose levels because it does not get digested. This makes fiber-rich food good for diabetics.