JAK...

According to one book I read on the energy costs of staying warm:

It takes 70kcal/hr just to keep the body alive; and
It takes 45kcal/hr to compensate for the heat lost by breathing in zero degree (F) air.

Carbohydrates burn the quickest, fats give the highest number of calories and last a long time, and proteins are the most EFFICIENT source of calories, but they are slow. I think not only do you need to increase your calories during winter, but you also need to base the fuel source you consume to the activity at hand. For stoking the fire at bedtime, a snack heavy in protein and fat, with a scosh of carb, will help keep you warm at night. In the morning you need to go heavy on the carbs and lighter on the fat and protein... you don't want to spend extra energy digesting a heavy meal. Lunch should be a combination of all three, heavier on the carbs again, but enough fat and protein to get you through the afternoon. Dinner could be heavier on the fat and protein, but give yourself time to digest before turning in. And don't forget to drink!!!!!

MNS