With the Jan. 9 premiere of “January Joiner” at New Haven’s Long Wharf Theatre, writer Laura Jacqmin ’04 is challenging two conventions of theater by confronting body-image issues on stage and bringing horror to live audiences for one of the first times.

The play, which Jacqmin called a “weight-loss horror comedy,” uses obesity as a springboard into issues of body image and poses questions about how people deal with changes in their loved ones. Jacqmin added that the play challenges the notion that only skinny actors belong on stage, instead featuring a cast of people with “normal” bodies.

By casting only thin actors in plays, theater companies set dangerous expectations of beauty that eventually get absorbed into culture at large, Jacqmin said. But rather than treating weight as an object of embarrassment and magnifying the challenges of being overweight, “January Joiner” treats an individual’s weight as a fact of life, director Eric Ting said.

Ting recalled how 20 minutes into the first rehearsal for the show, one of the actors frankly asked whether they could admit their issues with body image out loud rather than tiptoeing around them.

“The more we work on this, the more I’m surprised that we don’t really talk about this fact in theater,” said Meredith Holzman, an actress in the play. “This play breaks some rules, and overall it’s been a very empowering experience because so much of the play is about being accepting of who you are and of other people when they go through a change.”

In fact, the central story of “January Joiner” is one about family, as two sisters, played by Holzman and Ashlie Atkinson, enroll in a weight-loss program together, Ting said. The play uses weight loss to spark a transformative journey and to explore the consequences “when the people who have loved us all our lives start to see somebody different,” Ting said.

When the two sisters start their weight-loss regimen, they start to notice strange phenomena, including a seemingly haunted vending machine and the suspiciously low enrollment for their weight-loss session — both examples of how Jacqmin introduces horror to the play. According to Ting, horror is an uncommon element of theater productions because it is difficult to scare a live audience, given the limited special-effects toolkit available to stage teams. But for “January Joiner,” the production team was able to take advantage of the similarities between horror and comedy to incorporate elements of horror into stage theater.

“The great thing is that they’re both about timing — to successfully scare an audience is in many ways the same as making people laugh, because you need a good lead-in and punch line,” Ting said.

Jacqmin said she is happy with the hybrid of horror and comedy, since marrying the two genres produces great audience reactions. When audiences are already laughing, they are much more shocked by a show’s horror elements; at the same time, spectators can recover from their fright much more quickly in a comedic setting, she explained. Holzman said the complexity of balancing horror and comedy is fitting for the play’s themes of body image, change and family relationships.

While the Long Wharf attracts an older audience for its subscription tickets, Jacqmin said she thinks the unconventional elements of horror and body image will appeal to Yale students as well.

“This isn’t an easy take on weight loss — it’s more than a glancing comment,” Jacqmin said. “It’s something you will definitely be talking about in the cab on the way back.”

“January Joiner” will run at Long Wharf Theatre until Feb. 10.