BEVERLY HILLS, Calif. — In Netflix’s new anorexia movie “To the Bone” (which began streaming Friday), Lily Collins’ character Ellen has a compulsive habit of measuring her tiny arm. The young woman wraps her thumb and middle finger around her barely-there bicep to check that her fingertips meet. They usually do — that’s how sickly she is — and indicate how small Collins chose to get for the part.

Beefing up and slimming down for roles is all part of the job of an actor. But for Collins, 28, there was an added danger: She wanted to look like someone with anorexia, years after overcoming her own disordered eating, which included consuming nearly nothing, using diet pills and throwing up.

“I personally knew that this was something I needed to do to tell this story,” says Collins, who struggled with both anorexia and bulimia. “I wanted to be able to best exert my experiences on [Ellen] by going to the lengths I felt comfortable going to as an actor.”

That meant looking thin enough to worry her fans, who “lovingly, were concerned” after seeing the actress in paparazzi photos taken while she was preparing for the movie. She won’t disclose how much she lost, “but I was held accountable by a nutritionist, by [our director], by my mother, by our producer,” she says.

“There was never any time limit, there was never a [weight] number, [but] I didn’t want to get to the end of this experience and feel like I didn’t access what I needed to portray Ellen,” says Collins, who on this day at the London West Hollywood hotel looks radiant and “strong,” as the film’s writer-director Marti Noxon points out. “I can honestly say I gave it everything that I could and was able to stay Lily.”

For some scenes in the film, which shows Ellen getting gradually sicker with a bruised spine (the result of obsessive crunches), sunken cheeks, furry arm hair (the body’s way of keeping a too-thin body warm) and concave belly, Collins relied on special effects. “Makeup, in general, is amazing,” she says, citing a baggy wardrobe, collarbone and cheekbone prosthetics and plenty of lighting and shading tricks to make her look increasingly bony.

But then there’s the question: Even with the help of prosthetics, why take on a dangerous role at all?

Collins saw it as the right way to bring eating disorders into the public discourse.

It all felt serendipitous, because Noxon (who didn’t know about Collins’ past struggles) sent her the script just days after the actress wrote an essay about eating disorders for her memoir, “Unfiltered.”

“For me, it was a sign from the world saying, ‘This is probably something that is actually bigger than you. There’s a larger thing in play here and both are going to be able to better inform one another,’” Collins says. “When you have your life’s mission and the mission of a project merge like this so beautifully, that’s like total magic.”

To Noxon, whose own experience with eating disorders inspired “To the Bone,” making the film “was a weird thing of touching old hurts … to help people,” she says. “[Lily and I are] both recovered and healthy and living incredible, full lives beyond our wildest dreams. We can say, ‘Look, we’re here.’ “

Carly Mallenbaum, USA TODAY Network