Preheat oven to 350º. Lightly coat a 9x5-inch loaf pan with cooking spray.
In a large bowl, combine butter, oil, and sugar; beat with an electric mixer until smooth. Add egg whites and beat again until smooth.
In a medium bowl, combine flours, baking powder, and salt. Alternately add flour mixture and buttermilk to the egg mixture, beating after each addition. Add lemon juice, zest, and vanilla. Beat until smooth. Gently fold in frozen blueberries.
Pour batter into prepared loaf pan. Bake for 1 hour, or until lightly browned. Remove from oven and let cool for 30 minutes before slicing.