The trouble with that is that you'll probably won't be able to... While you won't starve to death for several weeks, nobody said anything about being fit for a 60 mile hike at the various stages of starvation.

The Swedish military survival manual (which is at least 20 years old, I'd love to see this verified or falsified) makes a bold statement that a healthy young male needs 500 kcal of carbohydrates each day to be able to operate at a functional level. Less than that and all the negative effects of food deprivation will leave most people in a poor state to fight the survival battle of their lives (no resistance to cold, poor cognitive skills, fatigue and so on).

This figure is (probably) based on some of those "hell week" excercises that they put some cathegories of military personell through: Give them 500 kcal and they'll still able to think and work, give them less and they essentially aren't.

As I understand it, no carbohydrates what so ever means your muscles are canibalized to be converted to something your brain can eat. Some carbs (500 kcal?) and you'll be very hungry, but you will burn your own fat reserves and can essentially keep going untill they run out. (According to the Swedish manual, a healthy young male has about 2-4 weeks before that happens).

Then again, there are those that claim that such nuisances as unable to keep warm, unable to think, unable to do hard physical work are mere transitional - that you can get into fat burning (ketogenesis), you will be decent functional, albeit at a lower tempo. I doubt those making that claim has ever tried it... Neither have I, for that matter. I doubt "cleansing" rituals as fasting (i.e. not eating for religious reasons) or extreme low carb diets in controlled circumstances has all that much relevance for a true survival scenario. BTW, Cody Lundin seriously suggests that everyone should try fasting every once in a while to see how it affects you personally - there may be large individual differences.