Considering the high-carbers say low-carbs suck on excercising, because they lack carbs, and some low-carbers report having sort of limitless energy ... I can safely say, we don't know Jack Squat.

High-carbers have their view based on similar dogma (eat carbs till you are "full", can't do anything without carbs) as nutritionists have about fat. Scientific studies about it? Fat chance.

Interestingly, and unsurprisingly, some studies I've seen about low vs med fat have shown improved stamina for the higher fat groups. A marathon is all about _saving_ those carbs. If your body is used to running high on carbs, it ain't saving them, it is USING them. Hence, hitting the wall.

Now as for people chronically "low" on carbs (should say with normal levels of carbs, current highcarb eating is the abnormality), fat is used much more. Hence, carbs are saved for when needed.

Again though, it is just speculation: they have their view, yet anecdotal evidence suggests otherwise. I've read a few reports on triathlon/marathon participants, and how they've managed to get their best ever results and still feel good on finish after being lowcarb for long enough.