Early Monday morning, a rental SUV with Georgia plates pulled up along a lonely stretch of road near Etna, New Hampshire. Out of the passenger seat slipped Karel Sabbe, a 28-year-old Belgian dentist, cinnamon roll in one hand and a small metal cup of water in the other.

It was not yet 4 a.m., and the damp morning was still as dark as dark can be. Sabbe’s best friend and crew member, Jorne “Joe” Biebuyck, opened the rear door of the SUV and readied Sabbe’s hydration pack. The two spoke a few words, alternating between Dutch and English, and then Biebuyck, clad in cargo shorts and flip-flops, accompanied his friend a hundred yards or so down the trail. A few minutes later, not even Sabbe’s headlamp was visible through the trees.

Sabbe was on day 34 of his attempt to break the fastest known time record for the Appalachian Trail, which stands at 45 days and some change, set last year by Joe McConaughy, a Seattle native now based in Boston. Both runners have been in a friendly competition since 2014, when McConaughy set the FKT for the Pacific Crest Trail. Two years later, Sabbe tore down that record by almost a full day, and his time still stands. He is currently on track to best McConaughy by a similar margin on the AT, too. If Sabbe is successful, he will become the first man to hold the FKT for the Pacific Crest Trail and the Appalachian Trail simultaneously. (Heather “Annish” Anderson currently holds both records for women on the trails.) It’s still early, but insiders say there’s a very good chance Sabbe will join Anderson in the record books.

“Karel has definitely got the trail cred,” says Peter Bakwin, who maintains FastestKnownTime.com and is widely considered the adjudicator of all things FKT. “He knows how to do this kind of long, multiday attempt in a supported style, and that kind of experience is invaluable on the trail.”

It also doesn’t hurt that Sabbe has taken tracking and transparency to a whole new level, Bakwin says. Prior to McConaughy’s record on the AT last year, a series of controversial FKT claims opened conversations about how to appropriately document and prove a record. Sabbe took note. And so, for this attempt, he is using a combination of data, including Strava and a GPS tracker that livestreams on his website. He and his crew are also asking at least two people a day to sign a Guinness World Records witness statement indicating where and when they observed Sabbe.

“We didn’t want to take any chances, and we didn’t want there to be any questions,” Sabbe told me on the trail. “We wanted everything to be public.”

That has endeared him to both the ultrarunning and hiking communities. So too has his approach to the supported hike: low-key and low-impact. Aside from some gear provided by sponsors, Sabbe has funded this attempt almost entirely out of his own pocket. In addition to Biebuyck, Karel’s only other constant crew support has been his wife, Emma, who sprained her ankle on the trail in Massachusetts last week.

On the day I met up with Sabbe, however, his small team was joined by Emma’s parents, who also reside in Belgium. The older couple had planned to rent a camper van or small RV for the trek but couldn’t find one that was handicap accessible (Emma’s mom uses a wheelchair), so instead the foursome drove as a convoy, meeting Sabbe at a few trailheads each day. At the first rendezvous, Sabbe was 16 miles into his 50-mile day. He paused just long enough to down two sodas and a bowl of noodles before heading out again. As he ate, his mother-in-law prepared mashed potatoes made with half a tub of margarine for the next stop. Emma handed him marshmallows and stashed chocolate bars in his pack. “We just have to keep stuffing him,” she explained.

Early on in his attempt, Sabbe dropped about eight pounds as he powered through challenging terrain in places like Tennessee’s Great Smoky Mountains. Meanwhile, Emma and Biebuyck struggled to figure out how best to keep him fed. (They estimate he’s eating about 10,000 calories a day.) In the end, the answer was right in front of them, Emma said. “Real American food—that’s pretty much all it takes.”

Pizza has been a favorite of Sabbe’s. So are cheese balls. And cheeseburgers—particularly Burger King Double Whoppers, which at 940 calories are close to twice that of a Big Mac. Sabbe also likes to eat Nutella straight out of the jar. “I am Belgian, after all,” he joked.

This week, Sabbe will tackle the White Mountains, including Mount Washington, notorious for its capricious weather and steep trails. From there, he’ll enter Maine, where the trail is no less challenging. His pace will slow, but that’s part of the plan. “I wanted my big days to be in the south, while I was fresh,” he told me. “This week and next, I can just be tired and speed-hike.”

He’ll still need to pull down super-high mileage—at least 30 miles a day—if he wants to beat McConaughy’s record and arrive at Mount Katahdin, the AT’s northernmost terminus, by September 1. As of now, that doesn’t seem like a problem. Sabbe thus far has kept to a schedule so regular that it has blown away even experts like Bakwin—on the trail each day by 4 a.m., run the equivalent of two marathons, knock off in time for dinner, and get to sleep at about 7 p.m.

In 34 days, Sabbe has yet to waver from that tempo.

“He may be Belgian,” Bakwin says, “but he runs like a Swiss watch.”