Hi Alan,
My foodless trips havent been past 3 days yet. And I didnt really notice to much problem. However you energy output would be much higher because of the extra stress and long distance. Mine havn’t been much more than 25miles a day. I am quite into alternate health etc.. and have been on many fasts of durations shorter than 6 weeks. I find that once your body swaps to ketonic generation of energy that your perceived energy levels are enormously higher. Look into the biology of fasting/starvation for more detailed explanations. I understand the possible toxic shock your talking about. At the end of 40 miles your body is really dead, so I guess that this would be much more prevalent if its not been given enough fuel.
Some extra thoughts though. Remember that its only 5 days and thus very little food is required anyway. I’m sure with that length and your determination to succeed you would more than likely lead to getting base weights way below 5lbs. If you feel that your body needs the extra fuel then I think oil is a good option (you may also like to try Ghee, has more flavour). I would really like to test this kind of exertion myself so I know my limits. I find that I do travel much better on a full stomach. It builds confidence and morale etc.. But I would think determination is the key here. Mental strength can easily overpower what the body feels.
I really have no idea about elevation changes as most of my hiking is low, flat to medium grade, warm and certainly closer to safety. I also have no idea about trails in America because I live in Australia. However I understand that I will go through this area in my attempted thru-hike in ’07. Is there possibilities of caching food at all?
I hadn’t even considered your question regarding body fat vs carried food. This is a very intriging question to me. I study biology and have had very little to do with human physiology. From what I can reckon in my head, essentially the food in the bag and weigh carried on body is going to have the same effect on knees, feet, back. However is the utilization of energy from food better than ketonic energy generation? That I don’t know. I was under the impression that it takes about 3 days for the body to start fully using body stores. But I really dont know the rate in which it can use them up. Something like a pound a day when under normal condition is most probable. I will have a look around and see what else I can work out because it is an interesting concept.