Yared Nuguse is worried about the gap in his résumé.

It’s just that becoming one of the fastest 1,500-meter runners in the world has upended the timeline he set out for himself at age 12.

“I was going to go to university, and then go to dental School, and just be a great orthodontist,” he said, 24 hours after becoming the American national champion in the 1,500 meters in July. “Then running kind of comes along in high school and it’s like, ‘OK, it doesn’t interfere with my plan,’ and then in college it doesn’t interfere with my plan. And it’s just like, ‘Oh, you could go professional now.’ And I was like, ‘Well, that kind of interferes with my plan a little bit.’”

After a fair amount of convincing, Nuguse, 24, decided to take a detour. Dental school would always be there, he figured.

In his rookie year as a professional runner, Nuguse — who was on the bowling team in high school, who has a turtle named Tyro after his favorite amino acid (Tyrosine), whose running mantra is “go out there and have fun,” who calls going to Taylor Swift’s Eras tour “forever a highlight” — has landed here, at the world championships in Budapest, as a top podium contender in the 1,500 meters.

When Nuguse recounts all that, he’s prone to giggling.

“I was never really an athlete type,” he said a day after becoming the national champion in the 1,500 meters in Eugene, Ore. “I still even now don’t really feel like an athlete type.”

His results says otherwise. In January, he set a new American record in the indoor 3,000 meters, running 7:28.23. He ran the second-fastest indoor mile in history in February, finishing the Millrose Games Wanamaker Mile in 3:47.38. In May, at a Diamond League meet in Rabat, he set a new personal best in the 1,500, running 3:33.02.

None of this would have happened had he not tried to beat the crowd at McDonald’s during high school gym class in his hometown of Louisville, Ky.

Students were assessed on their mile times, and Nuguse, a self-described “big nerd,” wanted to get a good grade, sure. But after completing the race, the students were allowed to go to McDonald’s — and Nuguse did a quick calculation. A win meant a good grade, plus, “I’ll eat there first.”

The high school track coach was quickly on Nuguse’s heels. The coach was persuasive, and Nuguse decided to give the track team a “solid try” to boost his college application.

Mike Kuntz, one of Nuguse’s high school coaches, remembers his first races well.

“You know Urkel?” Kuntz asked in a recent conversation at a cafe in Budapest. He stood up to demonstrate. “Yared would run a few strides, and then push up his glasses. Run a few strides, then push up his glasses.”

“He’d run in one shoe more often than you’d think,” Kuntz added, explaining that one of Nuguse’s shoes would somehow slip off during track meets or get stuck in the mud during a cross-country race. “And then he’d win.”

Nuguse continued racing with the team, surprised by how much he was enjoying it. Teammates started calling him “the goose,” a play on his last name, and soon the phrase “the goose is loose” caught on. In his senior year, Nuguse won Kentucky state titles in the 800 meters, 1,600 meters and 3,200 meters.

Running in high school was so much fun, he said, that he considered doing so in college when recruiters came knocking. By the winter of his freshman year at the University of Notre Dame, he had become one of the best milers in the country.

The word “fun” punctuates nearly every sentence Nuguse utters when talking about the sport. If he’s not having fun, he’s describing something that was “super fun,” “really fun” or, at a bare minimum, “kind of fun.” He knows that it’s somewhat of a superpower in a high-pressure sport that has a tendency to spit out even the strongest athletes.

“My mentality is so good because my whole being isn’t tied to running,” Nuguse said. “Running is fun and I love to do it, but I love to do because it’s fun, not because I’m really good and I have to.

“It’s just something I really enjoy for now,” he added, “and when I’m done enjoying it, then I’ll be done.”

An hour before he was set to compete in the N.C.A.A. national championship in 2019, Nuguse took refuge from the Texas heat in an air-conditioned car. He fell asleep. Matt Sparks, the director of track and field and cross-country at Notre Dame, needed to wake him up in time for him to win the N.C.A.A. title in the 1,500 meters.

“He wasn’t sitting in the car listening to loud music,” Sparks said. “He fell asleep in the car getting ready for what most would say was the biggest race of his life.”

As a professional runner with the On Athletics Club, Nuguse lives with and trains with Mario García Romo of Spain, his teammate and a fellow 1,500-meter specialist. They couldn’t be more different, said Dathan Ritzenhein, the team’s coach. “Mario is a list maker; everything needs to be order. If Yared knows what day of the week it is, that’s a good start.”

Nuguse is known to eat two Eggo waffles and “a ton” of syrup five minutes before he has to leave their apartment in the morning. If the frozen waffles were easier to transport, he would bring them to his international meets, Nuguse said, deadpan.

But he doesn’t stress too much about pre-race fuel. “As long as there’s something in my belly, it’s fine,” he said. “What I eat really just determines if I throw up or if I don’t throw up.” He smiled, realizing he didn’t vomit after his last race. “I picked well yesterday.”

On Wednesday, Nuguse will have his first opportunity to bring home an international title. He qualified for the Tokyo Olympics in the 1,500, but he was injured and did not compete, and he did not qualify for last year’s world championships.

Asked about his race strategy for the final, a stacked field that will pit him against the domineering Jakob Ingebrigtsen of Norway, Nuguse said he plans to “keep doing what I’m doing.”

Most of all he’s hoping to have — you guessed it — fun. He said he only plans on running professionally until 2028 or 2029, which he figures should give him enough time to see what he can do in the sport. He has six more years of school ahead of him — four years of dental school, and two years specializing in orthodontics — and he’d like to get on with that.

Until then, the goose will stay loose. When Nuguse mentions the Paris Olympics, he says it could line up nicely with Swift’s Eras tour dates in Europe. That would be awfully fun, he said. And, after that, he can have a stateside Olympics to look forward to.

“Winning in L.A. would be a dream come true,” he said. “But if I don’t, I’m not going to be like, ‘Well, my career was a failure.’ My career is a failure if I don’t have fun.

“That’s why that’s really the overall goal,” he added. “The medals, all the great accolades and stuff, it’s just highly sprinkles on top.”