Preheat your oven to 350°F (175°C). Grease and flour a 9x5-inch loaf pan.
In a mixing bowl, combine the all-purpose flour, whole wheat flour, baking powder, baking soda, salt, and ground cinnamon. Mix well and set aside.
In another bowl, combine the granulated sugar, brown sugar, and vegetable oil until well mixed.
Add the eggs one at a time, mixing well after each addition. Stir in the vanilla extract.
Gradually mix in the dry ingredients, alternating with the buttermilk, starting and ending with the dry ingredients. Mix until just combined.
Fold in the chopped pecans gently using a rubber spatula.
Pour the batter into the prepared loaf pan and smooth the top.
Bake in the preheated oven for 50 minutes, or until a toothpick inserted into the center comes out clean.
Remove from the oven and let the bread cool in the pan for about 10 minutes, then transfer to a cooling rack to cool completely.