Morgan Spurlock has gorged on McDonald’s and followed the lovable dweebs who populate Comic-Con in his feature documentaries. He’s tackled gun control issues and legal immigration on his incisive CNN show, “Inside Man.”

But the intense public reaction his work has elicited in the past — especially his breakthrough 2004 revelation, “Super Size Me” — can’t compare to the massive response expected from “One Direction: This Is Us,” the well-executed documentary Spurlock directed and co-produced about the most popular group in the world right now.

“We wanted to make a documentary blockbuster. Coming off (2011’s product placement study) ‘The Greatest Movie Ever Sold,’ we talked about wanting to do a commercially viable film,” Spurlock said recently from Philadelphia. “It’s a rare opportunity to tell the story of this band at this moment, exploding through time.”

Spurlock spent January through June on the road with the raffishly adorable U.K. quintet — Niall Horan, Zayn Malik, Harry Styles, Liam Payne and Louis Tomlinson — catching them in quiet moments backstage, goofing through soundchecks and spending increasingly rare private time with their families as they bounced around the globe.

Spurlock’s turnaround time for the 3-D film – also being referred to as “1D3D” – was a whizzing 10 months. But the shelf life of a boy band is fleeting, and Spurlock wanted to catch the phenomenon in action during their “Take Me Home” tour.

His biggest surprise? The group’s insanely devoted fans.

“I am constantly impressed with how dedicated their fan base is,” Spurlock said. “I’m a fan of things, but not to the point of camping out or chasing someone down the street.”

Spurlock said that spending time with the guys gave him a real appreciation of not only their hard work — which, he pointed out, the public doesn’t usually see — but also their determination not to let the madness that comes with teen heartthrob status ruin them.

“They’re so grounded. I was impressed by how grounded they are, how in touch they are with where they are in their career. They’re very humble,” Spurlock said.

One scene in “This Is Us” finds the group — whose origins as solo hopefuls cobbled into a group by mastermind Simon Cowell on England’s “The X-Factor” is explored in the doc — camping. It was Payne’s idea to set up at a campground in Stockholm after a show, and the scene, in which the friends discuss their future with preternatural insight, conveys the impressive self-awareness these young men possess.

Spurlock said it was never a problem getting footage, given the chatty nature of “five guys who have spent the last three years in front of cameras.”

And while many high-profile artists dispatch managers and publicists to censor or demand removal of scenes they find unflattering, Spurlock affirmed that, “We were kinda being left alone to make the cut of the film that I wanted to make.”

Cowell — who also appears in the movie — is still a presence in One Direction’s career, but, Spurlock said, the group largely steers its own path.

“Everyone wants to imagine that Simon is pulling these strings, but the boys have a tremendous amount of autonomy. They vote on everything — whether there will be more tour dates, on tour sponsors — it’s all democratic,” Spurlock said.

One Direction’s primary appeal is to a female teen audience, which also means that parents are tuned into the group. Don’t worry, mom and dad, because even off-camera, these kids are all right.

“These boys are thoughtful and they really care. You can’t teach empathy. We didn’t have to change much in the film (to make them parent-friendly) because they’re already such good guys,” Spurlock said. “We just had to make them themselves.”