During the winter it’s important to be adequately hydrated. Your body demands more water in the winter as your lungs lose moisture humidifying and warming the dry, cold winter air. The average person needs about 1.5 to 2.5 liters per day, whereas a winter exertions may require 2.5 to 5 liters per day. In order to burn fuel efficiently you must keep your body hydrated.
Avoid caffeine, alcohol and nicotine. Caffeine is a diuretic which causes water loss increasing dehydration. Although alcohol has some caloric value, it is a detriment in cold weather. Physiologically, alcohol creates peripheral vessel dilation which results in the rapid loss of body heat. Nicotine is a strong vasoconstrictor that decreases circulation to your extremities and promotes frostbite.
Eat a hot, hearty meal for dinner. Your body will use this fuel to keep you warm throughout the night. If the weather is really bad and you don’t feel like cooking a big meal, then cook the meal that is easiest and fastest to make. When cold-weather camping, you carry a freeze dried meal since they are a quick, easy hot meal.
Eating a a high calorie, high fat content snack before bedtime will give your body more fuel to help keep you warm. Proteins, such as cheese, nuts, or grains, are better than simple sugars. Proteins release their energy more slowly than sugars, keeping you warmer through the night.
Do calisthenics to get your circulation moving and your metabolism going. Take a brief hike around camp, or do jumping jacks or pushups to increase your metabolism and get warm before getting into the sleeping bag.
Go to the bathroom before bed and save yourself a middle of the night trip in the cold.