When Jonathan Neman was a student at Georgetown in the mid-2000s, he and some friends wanted to start a restaurant. A fast-food restaurant, but it would be healthy. And cool.

The documentary “Super Size Me” had made waves, and “we were going to be rejecting the fast food of the previous generation,” Mr. Neman said.

He and his business partners, Nicolas Jammet and Nathaniel Ru, opened the first Sweetgreen in 2007, on the edge of campus on M Street in Washington. As they expanded, they decided against franchising the brand, keeping control of every new location. Soon it became a buzzy millennial lifestyle brand. It sponsored an annual music festival. It went public in late 2021.

Sweetgreen now has more than 250 restaurants across the United States. The chain is known for its endlessly customizable salads — and for how quickly the cost of all those extra toppings and dressings can add up. (A recent lunch there cost me $16.28.)

The company also runs a growing number of locations that include what it calls the Infinite Kitchen, with salad-slinging robots that assemble bowls faster than human workers.

With great fanfare, Sweetgreen recently put fries on its menu — air-fried in avocado oil, to make customers feel better about adding a side of carbs to a salad. Much of its food is sourced locally, including avocados from California, which will limit the hit the company takes on tariffs, executives have told investors.

And Sweetgreen doesn’t cater just to office workers eating salads at their desks. Mr. Neman, 40, said he had heard that teenagers were “obsessed” with the salads, which wasn’t the case when Sweetgreen started. “The fact that they think that eating healthy is cool is something that we envisioned,” he said at his office in Los Angeles, where the company is now based.