Preheat the oven to 350 F. Grease a 12-cup muffin pan, or line with paper muffin cups.
In a large bowl, stir together the all-purpose flour, whole wheat flour, sugar, oat bran, quick-cooking oats, wheat germ, baking powder, baking soda and salt. Gently stir in the blueberries and walnuts. In a separate bowl, mix together the mashed banana, buttermilk, egg, oil and vanilla. Pour the wet ingredients into the dry, and mix just until blended. Spoon into muffin cups, filling all the way to the top.
Bake for 15 to 18 minutes in the preheated oven, or until the tops of the muffins spring back when lightly touched.