When a film wins the Sundance Audience Award it’s not usually because it’s some exercise in grim German expressionism. You’re usually talking about a fairly crowd-pleasing story, and Brittany Runs a Marathon is a good example of that. It stars Jillian Bell, the veteran of a bunch of popular comedies over the past decade, as a woman struggling with weight issues that she didn’t really begin to acknowledge until her doctor started using acronyms like BMI (Body Mass Index) and scaring her with prognoses of fatty livers. “So even my liver is fat?” she asks.

As we know from the many sad clowns that make their living doing stand-up comedy, a lively sense of humour is often a way to shield yourself from pain, and Brittany fits the bill. She’s one of those people who almost can’t get through a conversation without turning it into some kind of bit, but because she’s actually funny, that’s not as exhausting as it may sound. But it’s probably exhausting for Brittany, and she’s been self-medicating to help distract from her lack of a love life and, well, self-esteem. Until her divorcee neighbour (Michaela Watkins) convinces her to start running out some of her frustrations, and soon, she’s training for the New York City Marathon.

The title of Paul Downs Colaizzo’s film has a clever double meaning, which helps explain some of its narrative slackness. Brittany is literally running a marathon – or working toward that, anyway – but she’s also doing it figuratively. The road to better health and a together life is a marathon, not a sprint, and the film’s story circumlocutions help contextualise how many steps back Brittany might need to make before all her steps are forward.

A simpler film would show her life suddenly clicking, but Brittany still has some long, dark nights of the soul to get through, which include continued rejections both personally and professionally. That there isn’t an instant fix is why most dieters don’t keep the weight off. The title’s double meaning is something we extract from the film, not something that is explained to us in no uncertain terms, which is a real strength of the script.

Bell has thrived as supporting characters in films like The Night Before, Rough Night and Office Christmas Party, but Brittany Runs a Marathon gives her the showcase she proves clearly ready for. It’s not easy to play a character whose most salient characteristic, from a story perspective, is that she’s overweight, but Bell sets aside her vanity in a big way during the character’s darker moments.

It probably helped that in real life she was losing weight even though the producers did not ask her to, dropping 18 kilos for the role, the last of five of which where during filming. If she were going to do that anyway, why not lose the whole thing during filming? But shooting schedules don’t work like that, and anyway, the combination of real exercise and makeup allow for an amazing transformation that seems an awful lot like the real deal.

Brittany Runs a Marathon does meander a bit, introducing a love interest (Utkarsh Ambudkar) later in the story than we might be expecting, and spending time on tangents that don’t seem to fully pay off. But those elements are useful in terms of establishing a full portrait of this woman – who, it should be said, is based on a real person – and the thorny complications of her life. The extra story bits help show us why she’s not as quick to accept support as she should be, why she remains suspicious of people’s motives long after they seem to have proven themselves. And the longer we spend with her, the more satisfying it is when she’s proven herself – to herself.