He displayed knife skills and good culinary judgment, preparing a meal for me and his girlfriend, Jenny Uehisa, a designer for Patagonia (he is sponsored by Brooks Sports). We ate a Greek salad with cucumbers, tomatoes, loads of olives and seaweed; a stir-fry of vegetables with tofu and a miso and cashew sauce; and a mound of quinoa.

Where did he learn to cook this way? And more to the point, how does he survive? After all, I said to him, none of my running buddies, a group of nonelite but defiantly dedicated marathoners who train in Central Park, maintain as rigorous a schedule as his, and many claim to have trouble consuming enough calories even while being omnivorous.

“The whole issue,” he said, “is exactly that: getting enough calories. The first thing to worry about isn’t so much what you eat, but how much you eat. You have to take the time to sit at the table and make sure your calorie count is high enough. And when you’re a vegan, to increase your calories as you increase training you need more food. This isn’t an elimination diet but an inclusion diet.”

Jurek grew up in Proctor, Minn., eating cookie dough, canned vegetables and his share of fast food. When his mother, Lynn, developed multiple sclerosis (she died this spring), he and his siblings began cooking, but the food was, he said, “very Midwest — meat and potatoes.” In college, his diet began to improve, and as he “saw how much disease is lifestyle related,” he began eating “real food, eating the way people have been eating for thousands of years.”

He made the transition to less meat and more fish, then eventually knocked out dairy and other animal products entirely.

“It’s really a mental barrier,” he said, and he obviously has experience overcoming those. He said he needed 5,000 to 8,000 calories a day, “and I get that all from plant sources. It’s not hard, either. I like to eat, and I don’t have to worry about weight management. All I need is a high-carbohydrate diet with enough protein and fat.”