I also wonder about fat content. Over time, with enough fat intake, you burn fat more efficiently. But lots of us don't actually get enough fat. I feel much better since I upped my fat at jerseygirl's suggestion. I have more "staying" power, and don't burn out as fast. Don't exercise as intensely as you right now though. WHen I was quite intense during cross-country ski season last winter, I did eat more carbs, about 40g/day.
zen and the art of weight loss, finding the true path of en-lighten-ment