I guess I look at as "My body can only carry so much weight." I can either carry that weight as gear, gear plus fat, or fat. If gear includes food, then why carry the fat? In a survival situation your body will breakdown muscle before fat. Your brain can only function on two forms of calories, carbohydrates and ketone bodies. Your body only stores about 200 grams of carbs and that is almost enough to get you from dinner to breakfast. Ketone bodies are breakdown products of protein. I guess what I am trying to say is, if you know that you are going to be out for x number of days and are going to expend about y number of calories, you should take z amount of food such that the number of calories provided by the food is equal to or greater than the number of calories required, and leave the beer gut and thunder thighs in the gym.
Went elk hunting in Colorado a couple of years ago. A friend and I packed everything in, and packed the elk out. It was a 5 day trip and I was eating close to 5000 calories per day. I lost 12 lbs. Remember that water weighs close to 8 lbs per gallon. If you are sweating a lot and not drinking enough, it is easy to shed some serious weight.
Continuing with the wrestler theme: A friend of mine (name ommitted to protect the guilty) wrestled competitively in high school. His regimen for cutting weight before a competition consisted of getting hammered the night before (alcohol is a diuretic), and running on a tread mill in a neoprene wet suit before weigh in. Apparently it worked, the only match he lost was to the eventual state champ.
That big fat sumo wrestler could curl heavier weights if his arms had less fat.