One study tracked 65,000 female nurses (age 40 to 65); the other followed 43,000 male health professionals. Over the course of six years, a total of 1,438 developed diabetes. Men and women whose diet had a high glycemic index and low fiber content more than doubled their chance of developing diabetes. Foods that seemed to pose the greatest risk were white bread, white rice, potatoes, and sugary soft drinks. In contrast, whole grain breads and cereals (rich in fiber and with a lower glycemic index) appeared to reduce the risk of diabetes. Fruits and vegetables didn’t seem to have an effect, good or bad.