The fact-based, feel-good comedy Brittany Runs a Marathon is plenty funny and occasionally insightful, but without star Jillian Bell’s wit and dramatic depth, the script’s many weaknesses would shine even brighter.

Portraying the titular unhealthy (on pretty much every conceivable level) millennial who attempts to turn her life around by completing a certain 26.2 mile race in New York City, Bell is charming in Brittany’s messiness, heartwarming in her moments of growth, and an overall positive presence for writer/director Paul Downs Colaizzo’s feature film debut.

Though the bonds Brittany forms with runner friends Catherine (Michaela Watkins, Sword of Trust) and Seth (Micah Stock, Life Itself) and fellow house caretaker/crasher Jern (Utkarsh Ambudkar, Blindspotting) inspire steady laughs as well as scattered challenges that allow Bell to show her range, the film oddly presents weight loss and running in simplistic terms.

Perhaps meant to encourage people to take part in such healthy activities, as the pounds fall off and our protagonist’s running endurance increases, Brittany Runs a Marathon offers a  dishonest portrait of the willpower and time commitment required to get results.

What it gets right, however, is the social experience of being overweight, one full of encouragement and back-stabbing from various parties. But by glossing over the reality of improving one’s physical, mental, and emotional health in the name of a few more jokes and a crowd-pleasing ending, the film comes off as choppy and partially formed, and not on par with Bell’s outstanding commitment to her role.

Grade: B-minus. Rated R. Starts Sept. 6 at the Fine Arts Theatre

(Amazon Studios)