We must therefore look to a number of other sports, which will help us to undersdtand best practice. The longer triathlon is certainly something we can learn from, longer but still a single day event. Captain Scott lost his life because of many factors, nutrition being high amongst them. What about carbo , fats, protein, and vitamins. The answer is respectively, about 30-35 days and only three days in the case of food only.
Water then is quite important.
If we sit around in the house for 24 hours with average temperatures we'll lose around 2.5 litres. On a warm day, exercising then this same amount per hour is lost. Breathing, especially in dry conditions and snow environments can be particularly dry with huge water losses via the lungs. Solid foods will take water out of the blood system until it can assimilate those solids. Drinking, yes drinking.