P.S. Just to quantify the rate of weight loss by strenuous exercise versus water-only fasting, I lost 39 pounds in the first 104 days of my first long distance hike (see journal at http://jwleaf.org/html/solo93-1of7.html
), an average loss of 2.7 pounds of fat per day. By comparison, the loss rate during a water-only fast averages about 1.1 pounds per day because metabolism slows way down, not so when physically active. Therefore strenuous exercise with food limited to what can be carried in your backpack for a week at a time is better than fasting to lose a lot of weight quickly. The two methods cannot be practiced simultaneously.