In large bowl, stir together whole wheat and all-purpose flours, baking soda, salt and nutmeg. Make a well in center; add buttermilk and orange rind. Mix just until dough is soft but not sticky. Turn dough out onto lightly floured surface. Knead 10 times. Put dough into greased 8 x 4 in (1. 5 L) loaf pan. Bake in 350F (180C) oven 20 minutes. Reduce temperature to 300F (150C); bake 25 to 30 minutes longer or until a cake tester inserted in center of loaf comes out clean. Turn out onto wire rack.