Coat a 9 x 5" loaf pan with cooking spray. Line the bottom of the pan with parchment paper, and coat with cooking spray.
Weigh or lightly spoon flours into dry measuring cups, and level with a knife. Combine flours and next 6 ingredients (through salt). Combine buttermilk and egg; add to flour mixture. Stir just until combined.
Spoon the mixture into prepared pan. Bake for 1 hour and 5 minutes or until a wooden pick inserted in the center comes out clean. Invert bread onto a wire rack, cool completely. Remove parchment; slice bread into 12 slices.