I've done marathons for at least 10 years. Also 50 and 100-mile races. With Atkins I lost some weight but have found I am not running faster. But I'm finding that after the run I don't have the serious muscle soreness that I used to develop. I think for training and racing you must include some carbos or you won't be able to run your best.

While running, carbs are shunted into the muscles without the use of insulin. So I wouldn't forego carbs. If you do, you won't be able to survive a marathon. Just my opinion as a veteran runner.