Love2, it is my understanding after some pretty extensive reading, that you need carbohydrate to exercise intensely. Even easy running gets a large percentage of its energy from carbohydrate. It is just the way the body works. If you run out, intense exercise pretty much stops--you bonk, or hit the wall. I've done it, it isn't pretty! Fat burning can go on much much longer, but it doesn't provide as much energy as quickly, like you would need for running.
Having said that, I know there are people around here who do lower carb diets, which would tend to deplete the glycogen stores, and still manage to run, quite happily at that. I don't understand how that works, but obviously it does for some people. You could try that and see if it works for you--everybody is different. For me, I need my carbs, and when I increase mileage, my cravings for them goes up as well. And if I don't eat more, I'll literally start to feel sick.
From a weight loss perspective, a calorie is pretty much a calorie. There's a pretty good thread on the exercise board somewhere about the myth of the fat burning zone.
I think this is the link: http://www.3fatchicks.com/forum/showthread.php?t=52700
I also found a Runner's World article that has similar info for running:
http://www.runnersworld.com/article/...-0-628,00.html
Anne


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