The True Story Behind 'Brittany Runs A Marathon' Is Just As Damn Inspiring

The new film Brittany Runs A Marathon tells the tale of Brittany, a fast-witted, twenty-something party girl living in NYC who doesn't feel so hot about her direction in life...or about herself. After a rude awakening from her doctor, who advises her to lose 45 pounds (which Brittany hilariously reminds him, is the same weight as a grown Siberian Husky), she begins to take stock in her lifestyle choices. So in an attempt to set her life on a healthier course, Brittany (played by Jillian Bell) decides to take up running...and ultimately sets a goal to run the New York City Marathon.

The rest of the film is filled with friendship ups and downs, family dynamics, heartbreak, self-discovery, and plenty of snarky quipsall of which result in a film that's bound to leave you in fits of laughter and joyful tears by the end (it's def not just me).

What's even more incredible about this uplifting film is that it's actually based on a true story. That's right, there's a real Brittanyand she's just as inspiring, funny, and badass IRL. Here's everything you need to know about the leading lady of this marathon success story. (Warning: Spoilers ahead.)

The real Brittany is writer Paul Downs Colaizzo's close friend.

Brittany ONeill and Paul Downs Colaizzo BusinessInsider USA Images

Writer-director Colaizzo was inspired to write this film after living with his dear friend Brittany O'Neill. They were friends in college, but had fallen out of touch after graduation. "Then I needed a place to live, and she needed a roommate. And really quickly, we started having deep friendship talks," said Colaizzo during a Q & A following the Brittany Runs a Marathon Screening with Betches Media .

"And it was during one of our conversations, that she decided to go for a run, and I thought: Well, this is a movie."

She wasn't the partier you see in the movie...but she didn't love her lifestyle.

While movie Brittany seemed to go out binge drinking with her friends nearly every night, and didn't care about her job in the slightest...O'Neill wasn't quite so reckless.

"At the time, I was running a theater company, and that lifestyle lends itself to grabbing a drink before the show, then grabbing drinks with the cast after. So by the end of the night youve had a lot of drinks and youve eaten a bunch of BS food like chicken fingers," O'Neill told Women's Health. "It wasnt atypical of a twenty-something in New York city. But it was definitely unhealthy and fairly messy."

O'Neill's decision to start running was gradual.

While in the movie, Brittany's visit to the doctor is somewhat of a catalyst for her lifestyle changes, in real life, O'Neill says there wasn't one single moment that swayed her.

"I just felt like I was so much more put together than my body gave away. There was a mismatch between what my body was portraying and what I felt I was like. So I just wanted to make a change," she says. "I spent so much time fighting with myself about whether I should need to change. And then I just gave up on deciding whether or not I should, and just decided it was time." So ultimately, it was a more cumulative decision. "I just thought...why not start now?"

View this post on Instagram Brittany and Britta... er, @jillianbell have a message for you! #BrittanyRunsAMarathon A post shared by Brittany Runs A Marathon (@brittanyrunsmov) on Aug 20, 2019 at 9:51am PDT

Brittany suffered from an even worse injury IRL.

In the film, Brittany realizes she's injured after running a half marathon. She's diagnosed with a stress fracture , and forced to (somewhat comically) walk around with an air cast.

O'Neill on the other hand, suffered a bone spur and tendon tear in her ankle that made her basically immobile for two months. "It wasnt until two years later that I was able to run the marathon," she says. "I had a tendon tear and a bone spurs, which required surgery. So it took a whole two years for me to get the surgery, and recover, and build my miles back up."

This setback hit her really hard. "I could have used the time in my recovery to learn a language or get core strength . But I wallowed in the injuryit was a huge step back for me mentally and emotionally." Still, she now sees the setback as a major and crucial part of her journey. "If I had just decided to run the marathon, then did it, I dont think I would have come as far as I have with my relationship with myself and my body."

The strange part is...Colaizzo actually wrote that the character Brittany got injured before it happened to O'Neill IRL. Freaky!

The characters Catherine and Seth didn't exist.

While O'Neill did join a running group to help her get through those longer miles (North Brooklyn Runners, to be exact)...there were no IRL manifestations of the movie characters Catherine (Michaela Watkins) and Seth (Micah Stock).

Brittany\'s marathon time in the movie (3:55:57) was her exact time IRL.

However, O'Neill did get a lot of help from the runners she met in the group. "So many of them had run marathons before, so I was able to ask so many questions and get a lot of advice about tips and tricks," she says.

And although she didn't have a running buddy like Seth, Colaizzo admits that the character is partly inspired by his own relationship with O'Neill.

Brittany's toxic friend Gretchen wasn't exactly real, either.

In the movie, Brittany lives with her social media influencer BFF Gretchen (Alice Lee) until (spoiler) a pivotal turning point in the film when Britany cuts ties. And while O'Neill didn't have a specific friend that inspired this character, Gretchen isn't totally fictional. "I think she is the personification of my negative self-talk in a way, and those awful thoughts that can run through your own head."

O'Neill also adds that at this point in her life, she was taking stock in her friendships, and asking herself if they were valuing her, and vice versa. "I think [Gretchen] was a way of showing how common those toxic friendships can be."

Brittany did find love...just not with Jern.

I'm sorry to report that O'Neill did not fall in love during a housesitting job in her actual life. BUT! She did find a different love interest at the time.

View this post on Instagram Dating is like running- you just have to get started sometimes #RunBrittanyRun A post shared by Brittany Runs A Marathon (@brittanyrunsmov) on Jul 19, 2019 at 11:01am PDT

Remember how in the movie she creates an OKCupid profile? Well, as it turns out, that's how she met her (now husband!) Jason. "We met at the same time as when the characters met. At the same point in the journey," says O'Neill.

And, funny story: "Weirdly, when I first wrote Jern, his name was Tiger," says Colaizzo. "And one of the first times I hung out with Jason, her now husband, after Id changed the character name, he was wearing a shirt with a tiger on it, designed by his friend Jern." Coincidence? Fate? Who's to say.

Brittany totally rocked her marathon IRL.

One of the most nail-biting scenes in the whole film is when Brittany reaches the last couple miles of the marathon, and nearly gives up. But with the help of her friends cheering her on, she pushes through. (Was anyone else sobbing during this part?)

However, in real life, O'Neill basically ran a dream marathon, without hitting any walls. "I had the best time. I was just grinning for four hours. Two million people came out to cheer, so there would be six people deep screaming my name, and I felt like a rockstar," says O'Neill. "And every mile or two I had friends cheering me. Paul was there, he met me at several points, then met up with me after."

Oh and her time in the movie: 3:55:57? Yeah, that's the exact time she ran IRL. Go, Brittany!

While some characters, names, and events changed...the journey was 100 percent the same.

2019 Sundance Film Festival - "Brittany Runs A Marathon" Premiere BusinessInsider USA Images

"The emotional journey is dead on. Every time I see the movie, I feel like I learn something new about myself and my journey," says O'Neill, reflecting on her portrayal in the film. "But I dont think thats entirely because the movie is inspired by meI think its an incredibly relatable and personal story."

Brittany Runs A Marathon opens in select theaters Friday August 23rd.

Check it out here!