They’ve gone from fast food to extremely slow salads.

New Yorkers trying to make good on “eat healthy” resolutions are mobbing salad joints — leaving many on long lines cursing their radicchio-strewn diets.

“You guys can go f–k yourselves!” one very hangry businessman in a Patagonia puffer vest was overheard telling his colleagues at lunchtime on Thursday, as he ditched the 100-plus-long line at Chopt on West 51st Street, between Sixth and Seventh avenues.

“The last few days after New Year’s have been crazy because of the resolutions and people wanting to eat healthy,” said another business-suited, kale-clutching customer there.

“Yesterday, there was a line out the door,” Maya Dillon, 46, said as she left Just Salad at East 51st Street and Park Avenue.

“It’s always the busiest time of the year, right after New Year’s,” said one worker.

“Everyone decides to be healthier for their New Year’s resolution.”

It’s no wonder that nearby fast-food joints that offer less leafy lunches are seeing a slowdown.

“Usually, it’s very, very busy,” said a security guard Thursday at McDonald’s on East 42nd Street between Madison and Fifth avenues. “Today — very, very slow.”

It was also “extra slow” at the Chick-fil-A at East 42nd Street between Vanderbilt and Madison avenues, an employee told The Post.

“In December, there were a lot of tourists and it was very busy,” said another worker there.

“Now in January, you see a dip in business.”

Meanwhile, at Sweetgreen on East 55th Street, Julie Pastor, 30, had to wait in a line of 50 people to get her guacamole-and-greens bowl.

“The line was outside the door and wrapping around the sidewalk,” she said.

“It’s a psycho line,” agreed another customer.

Salad joints are feeding the ­frisée frenzy with seasonal promotions.

Sweetgreen offers a New Year’s resolution reward program; Chopt is hyping its lowest-calorie salads.

“New Year’s resolutions as easy as one, two, three — all under 400 calories,” Chopt says on its Facebook page.

Sales and lines do grow after New Years, said Sweetgreen co-founder Nicolas Jammet — but the company tries to offset that by encouraging online ordering, including through Outpost, a no-fee delivery service to corporate offices.

“We know resolutions can be hard, but our goal at Sweetgreen is to make eating real food easy,” said Jammet.

Additional reporting by Laura Italiano