Preheat the oven to 350°. Spray a 9-by-5-inch loaf pan with cooking spray. Bring a medium saucepan of water to a boil. Add the carrots and boil over moderately high heat until tender, about 15 minutes. Drain and mash the carrots with a potato masher. Let cool.
Meanwhile, in a pie plate, toast the walnuts for about 7 minutes, or until lightly browned. Let cool, then coarsely chop.
Sift the flour with the baking soda, nutmeg, cinnamon and salt. In a large bowl, whisk the eggs with the sugar until pale yellow. Whisk in the oil and buttermilk. Stir in the carrots and walnuts, then stir in the flour mixture until blended.
Pour the batter into the prepared pan and bake for 50 minutes, or until risen and a cake tester inserted in the center comes out clean. Let the loaf cool in the pan for 10 minutes, then turn it out onto a rack to cool completely.
The loaf can be wrapped in plastic and stored for up to 3 days or frozen for up to 1 month.
One Serving 312 calories, 13.2 gm total fat, 1.4 gm saturated fat, 46 gm carb.