Even if you don’t run, chances are high that you’ve heard how carbo-loading helps athletes who partake in endurance sports—particularly marathons.

But ultramarathoner Dean Karnazes is turning conventional running wisdom on its head by embracing a Paleo diet. In other words, no refined carbs.

running dogs

The 52-year-old marathon vet once ran 50 marathons in 50 days, including an impressive 350 miles with a time of 80 hours and 44 minutes.

Like many runners, the guy burns a lot of calories, so he’s basically eating all the damn time. But unlike a lot of runners, he’s stopped believing in the healing power of carbs.

So what’s the logic behind this theory? Monique Ryan, R.D., the author of Sports Nutrition for Endurance Athletes, explains that energy from carbs gets stored in your body. When you run a marathon, your body burns both glycogen and fat as fuel. Glycogen stores also help hold water, which can help you stay hydrated during a race.

running hit a wall

The problem is that glycogen burns much more efficiently than fat. So when your body runs out of glycogen stores during a race, you can hit a wall where your body demands that you slow down.

But Karnazes admits that he wasn’t always thoughtful about his diet. He once ordered a pizza using a cell phone and credit card while running a marathon, and had it delivered to him as he ran.

Karnazes summed up his old attitude:

“I used to live on junk food, thinking that since you burn 30- to 40,000 calories on some of these runs, you need to get as many calories as you can no matter how you get them in.”

Are we drinking ourselves to death? http://goo.gl/VYNseb

A photo posted by Dean Karnazes (@ultramarathon) on

He didn’t notice energy problems while running marathons, but did pick up on huge fluctuations in his energy levels on off-days. That’s when Karnazes started experimenting with his diet, focussing on fruit, vegetables, yogurt, and cold-water fish. The only non-seafood meat he eats is organic, free-range bison cooked ultra-rare.

Karzanes abides by the following rules:

  • He eats 8,000 to 10,000 calories a day when he’s preparing for a race or other big run
  • Base calorie intake is 3,200, to which he adds anywhere from 300 to 500 calories per hour he expects to spend running
  • Most carbs in his diet come from fruits, which Karnazes eats whenever he feels hungry

For more details, check out GQ‘s interview.

[via GQ]