I am also reading this book and have read other articles like it. I would clarify the elevated heart-rate comment. Stu reccomends keeping your heart-rate at an aerobic level without going anearobic. You burn fat in the aerobic zone, but burn glucose in the anaerobic zone. You store enough fat to run marathons but only enough glucose for about 20-30 minutes of anaerobic activity, unless you take in more glucose (carbs). I am an endurance cyclist and I can do 6 hour rides on zero carbs days before, during, and for days after. The body can run better on fat burning than carb buring of you train properly! The key is to train right near your aerobic/anaerobic treshold and gradually work it higher. Heart rate monitors can help a lot.