Don't equate Raisin Bran cereal with All- Bran cereal. All-Bran is the best source of insoluble fiber in the American Diet. In fact, it's virtually the only good source. Although the glycemic load of All-Bran pushes the upper limits (85 for a half-cup), it's worth eating because of the fiber. However, Raisin Bran is another story. It provides much less fiber, and its high refined flour content and the raisin in it makes its glycemic load unacceptable. If you want to reduce glucose shocks and lessen your body's demands for insulin, Raisin Bran is a bad way to start the day.