An ultramarathoner is someone who regularly runs races that make the standard 26.2-mile contest look like a morning jog. Scott Jurek, 37, is an ultra ultramarathoner. He's the U.S. record holder for the 24-hour run, having covered 165.7 miles in a single day. Twice he's won the brutal Badwater race—135 miles through Death Valley—and he's won the 100-mile Western States Endurance Run seven times. And he does it all on a diet devoid of animal products. In his free time, he helps restore the mountain trails so central to his sport.

Q: How long have you been vegan?

A: Since 1999. I started doing ultramarathons in '94, but all my major victories happened after I changed my diet. It really impacted my health and my training, and it's been a big reason why I've been so consistent with pumping out serious results.

"Becoming vegan wasn't like, 'Oh, I can't eat this, I can't eat that.' It brought so many new ways to explore cooking."

Q: What made you want to go vegan?

A: Definitely it got spurred from the health standpoint. At the time, I was eating fast food four times a week. You name it—extra-large fries, double McChicken sandwich. I used to hate vegetables, and I used to hate running. I used to hunt and fish; in my family, that's how we explored the outdoors. A major turning point was reading Dr. Andrew Weil's Spontaneous Healing, and then Howard Lyman's Mad Cowboy. I realized that our three meals per day play a huge role environmentally. I've come to appreciate the ethical issues too. As a former hunter and fisherman, I'm sympathetic to people who do those activities, but I'm also sympathetic to the fact that we do mistreat animals raised for food.

Q: You run mainly on trails, right?

A: My first choice is to run in the mountains, because having such a beautiful setting brings you back to that primal instinct. When I'm on a 40-mile run, I get to explore places that would take most people four days of backpacking [to reach]. I'm moving through incredible scenery and still soaking in the sights and sounds and smells.