There are actually some runners here in Sweden who run long distance races... like a double marathon in the woods, mainly on fats and protein. I don´t think they stick to zero carb between races, but they eat mainly fat and protein. I think they actually eat pemmican during the race.
I have been zero carb during times when I have gone for windsurfing. It feels like i have had i bit more stamina. But maybe the recovery have been a bit worse.
But i think we are losing one important fact here.. It´s a lot easier to get a lot of energy from fat than from carbs... If you gonna get 2000kcal extra from carbs thats like 500grams of carbs -thats kind of hard to eat - not to mention the health effects. If its from fat thats like 220g - thats really easy to eat and you don´t feel like u are smashed to the walls afterwards.
