Place the oat bran, baking powder, and baking soda in a large bowl, and stir to mix well. Add the buttermilk, honey, egg whites or egg substitute, and vanilla extract to the oat bran mixture, and stir just until the dry ingredients are moistened. Fold in the raisins, nuts, or blueberries, if desired.

Coat muffin cups with nonstick cooking spray, and fill three-fourths full with the batter. Bake at 350°F for about 14 minutes, or just until a wooden toothpick inserted in the center of a muffin comes out clean. Be careful not to overbake.

Remove the muffin tin from the oven, and allow it to sit for 5 minutes before removing the muffins. Serve warm or at room temperature, refrigerating any leftovers not eaten within 24 hours.