Spurlock — who made his name with socially engaged documentaries such as "Super Size Me" and "Where in the World Is Osama Bin Laden?" — is on a mission to convert unbelievers (and even Beliebers) into One Direction fans.
"These boys are so charming and so fantastic, I challenge you to go to the movie and not like them after the film is done," Spurlock said Monday at a news conference with the band ahead of the movie's world premiere Tuesday in London.
"Part of the reason they've been so incredibly successful with their fans is that they are so incredibly grounded and normal, and that's what comes off in the movie. ... You see five guys who are the same five guys they were three years ago."
Three years ago the five teenagers auditioned individually for TV talent show "The X Factor," where svengali Simon Cowell had the idea of putting them together as a boy band.
They didn't win the competition, but they went on to top charts and win young hearts around the world with their cheeky personalities and ever-so-slightly edgy pop.
Part concert movie, part behind-the-scenes documentary, "This Is Us" follows One Direction on the road, from London to Tokyo to Mexico City. It promises to show the group as fans have never seen before — up close, personal and in 3-D.
Spurlock was given access to the band members' families as well as to the band members themselves at home, in hotel rooms, in stadiums and on tour buses — though it's unlikely to be a completely candid, warts-and-all look at the band. Cowell is a producer on the movie, which is aimed firmly at the young global army of "Directioners" who helped make the lads stars.
Spurlock has said he was drawn to the movie by the chance to experience the closest thing our decade will see to Beatlemania.
"You suddenly realize it isn't just a British or an American phenomenon," he said. "Everywhere they go they are being chased by hordes of fans. We were in Mexico City and there's 5,000 people camping outside the hotel. This is such a massive global phenomenon, and it's only growing. It was incredible to see."
For the band members, whose feet have barely touched the ground since 2010, it was a rare chance to reflect on how far they've come.
"Because so much is happening to us you kind of just lose it all," said Louis Tomlinson. "It's great just to sit back and watch it back and remember and relive those moments."
Band mate Liam Payne said making the film had been "nerve-racking." But the lives of the five young men — none of them over 21 — have become so surreal that the experience of being filmed offstage and even in bed was almost normal.
"In a way it was really strange having the cameras around, but at the same time it didn't make that much difference," said Harry Styles. "It was kind of just getting on with your day while having someone in your way when you're trying to get out the door."
The band members gently deflected questions about whether scenes of partying or other debauchery had been left on the cutting room floor.
"We like to think we're rock 'n' roll, but we're not, really," said Tomlinson. "It's a shame."
"One Direction: This Is Us" opens in Britain Aug. 29 and in the United States Aug. 30.