The other factor is hydration. In cold weather, it's insidious -- you have to force yourself to drink (guzzle) because you don't feel thirsty at all.

Thing is, your body needs a ton of water to metabolize all the high-energy food (esp. fats) you've been ingesting. Assume you are always dehydrated, and monitor your input with a sceptical eye. Your body will fool you.

Old timers had a "mug-up" every few hours, and it wasn't for warmth. Tea, tea, and more tea!