This entire interview with Steve Phinney is fantastic and worth reading (or listening to):

Earlier this summer, Steve Phinney and Jeff Volek, authors of The Art and Science of Low Carbohydrate Performance, headed to the Western States 100-mile Endurance Run, to study how runners in this grueling race fared, literally, for they were checking how the athletes performed, AND how they ate. Steve Phinney says that more and more endurance athletes are choosing low-carb, high-fat. They’re choosing this diet both to get over digestive problems that hit in such a demanding event, and to win the race, and win it BIG! That’s what Tim Olson did this year. A self-proclaimed low-carb eater, Tim won the race — with a record-breaking pace

Here's a brief quote from the actual interview, but it's definitely worth the time to listen or read the entire thing. The study is incredibly interesting and when the full results are published I will provide an update to this.

A low-carb runner WON the race?

STEVE PHINNEY: That’s correct. His name is Tim Olson. He lives in Oregon, and he says he made the transition to low-carb about a year or so ago. Tim won a 100 mile race, I think, in late fall or early winter, and so he had already demonstrated he can do the event on low-carb and when he came into this Western 100 race, his goal was not just to do the race. He stated in advance that his goal was to win it. So he ran at the front of the race. He was running with a number of other very accomplished male competitors — people who had done this race before and placed well before. Somewhere between mile 65, well, he went through the checkpoint at mile 65 a couple minutes ahead of the next guy, and there were a group of of four runners who were within four of five minutes of each other around them. But when he passed the checkpoint at mile 85, he had opened the gap somewhat. Then between mile 85 and 100 — and keep in mind, by mile 85 Tim Olson has already run the equivalent of over three marathons — somewhere in those final 15 miles, Tim Olson opened up an an additional 15 minute gap between himself and all the other runners. That means, after running 85 miles, he was able to put on a burst of speed at the end of the race, and he finished 15 minutes ahead of his next closest competitor.

Tim Olson finished 15 minutes ahead?

STEVE PHINNEY: Yes, but more importantly he knocked 21 minutes off the overall time course record.

...

STEVE PHINNEY: Some of it is Tim Olson’s inborn, God-given talent as an ultra endurance runner, but some of it has to do with the diet he’s switched to eating – a low-carb diet. We don’t have the details of it, but typically the low-carb runners eat far less during a race. A high carb racer may eat 6,000 in-race calories. But typically a low-carb racer will eat 2000 calories a day during the race, or less. And the better adapted the racer is to low-carb, they find the less they have to eat.