Preheat the oven to 350°F (175°C). Grease a loaf pan.

In a mixing bowl, whisk together the buttermilk, vegetable oil, egg, and vanilla extract.

In another bowl, combine the all-purpose flour, whole wheat flour, sugar, baking powder, baking soda, and salt.

Gradually add the dry mixture to the wet mixture, stirring until just combined.

Gently fold in the blueberries, being careful not to overmix.

Pour the batter into the prepared loaf pan and smooth the top.

Bake for 55-60 minutes, or until a toothpick inserted into the center comes out clean.

Allow to cool in the pan for 10 minutes before transferring to a wire rack to cool completely.