Mix the whole wheat flour, all-purpose flour, nutmeg, cinnamon, salt, baking soda, white sugar, and light brown sugar together in a large bowl. Fold the vanilla extract, eggs, vegetable oil, lemon juice, and zucchini into the flour mixture one ingredient at a time with a rubber spatula; divide the mixture between 2 loaf pans.
Bake in the preheated oven until a toothpick inserted into the center comes out clean, 65 to 75 minutes. Cool in the pans for 10 minutes before removing to cool completely on a wire rack.
