I'm talking about the "former fat girl" trope, and there are more versions of it than you can possibly imagine.
You can find this character archetype in a lot of hit television shows including "Futurama," "One Tree Hill," "Pretty Little Liars," "Friends," and "Glee" — that's only a handful of examples.
The trope was intensely popular in the '90s and early '00s, but it still manifests itself in some of today's most popular titles.
Although former fat characters all differ slightly, they share a handful of key problematic traits.
Rachel Gatina from "One Tree Hill" is the perfect distillation of all the characteristics I'm about to explain. She transfers to the show's fictional high school mid-series and is introduced as a promiscuous villain. It's revealed later that before her transfer, she was fat — and that she underwent gastric bypass surgery to lose hundreds of pounds before emerging at her new school as a more attractive and less empathetic person.
They all lose an extreme amount of weight in a dangerously short time frame — so much so that other characters find them unrecognizable upon their "re-entry" to society.
In the 2007 parody film "Date Movie," the protagonist undergoes a "Pimp My Ride"-style makeover in which she's likened to a fucking CAR as her body is made "acceptable" for a dating show. This extreme take is obviously just for shock value, but subtle iterations of the transformation are far more sinister.
In cases such as Hannah Marin from "Pretty Little Liars," the fat girl in question goes unseen for a few months (most likely a summer vacation) and returns so much thinner, she's practically a new person. How the weight is lost is addressed vaguely, allowing the viewer to believe the loss was achieved easily via diet or surgery rather than a developing eating disorder or extreme fitness regimen.
(This trope's romanticization of weight loss surgery is another story entirely.)
Most of them have intense relationships with food that are just as damaging as the drastic weight loss methods.
In season one of "Pretty Little Liars," Marin is forced to relive her past (read: fat) life by... eating in public. The super-villain known as A blackmails her into eating six pig-themed cupcakes before suggesting she "get rid of it" by purging. She's sent into a spiral of flashbacks during which the viewer associates food with trauma, bullying, and unpopularity.
Monica Geller from "Friends," on the other hand, becomes a world class chef in her thin adulthood, and it's seen as an ironic miracle she achieved her career status without gaining her weight back. Sure she can cook as much food as she wants, but she never really touches it.
This trope also suggests that to become thin is to become valid as a person — characters in the midst of a "fat phase" are often used as a point of humor or tragedy.
Geller is the biggest example of this, without a doubt. "Fat Monica" is seen frequently in flashbacks throughout most of the series, and her body is a walking punchline. She's clumsy, overexcitable, and perpetually crushing on someone — for Geller, being fat is equatable with being naive. It isn't until she becomes thin that she's seen as a human being rather than a comedy prop.
Sometimes, these characters lose weight for the sole purpose of seducing men who scorned or ignored them pre-weight-loss.
I shit you not, there's an entire episode of the hit ABC Family program "Greek," about a mysterious leather-clad woman who crashes a fraternity and attempts to seduce Cappie, the show's male protagonist. Toward the end of the episode, he realizes that she's actually a former fat girl who had a crush on him when they were children. It turns out she was on a post-weight-loss mission to have sex with him as revenge for not noticing her at summer camp. This was the season's Halloween episode; THIS WAS SUPPOSED TO BE A HORROR PLOT.
Back to Geller. As a late teen, she lost over 100 pounds in a year after she overheard her crush, Chandler Bing, refer to her as "Ross' fat sister." About a decade later, in one of the show's most beloved episodes, she marries him.
Finally, these characters are almost always complete and utter assholes once they're thin.
Men aren't safe from this played-out schtick, either. Take Schmidt from "New Girl," for example. He loses weight after college following a lifetime of being bullied for his size, and he's one of the most outwardly narcissistic characters TV has ever known. Whereas "fat Schmidt" was timid and pathetic, "thin Schmidt" is selfish, snobbish, and obnoxious.
TLDR, the message this trope is trying to achieve is this one: If you have or ever had a body type that breaks society's unattainably thin standard, you are not — nor will you ever be — considered "normal." Point blank.
Watching fat girls become thin girls with ease time and time again can mess up a person's body image in uncountable ways — especially a young woman's.
Like "Glee's" Quinn Fabray, I was convinced as a teen that I could drastically change my body, which I hated, in a single summer — that there was a thin person inside of me who would solve all of my problems once she emerged. For Quinn, that sentiment was true: She lost weight and transferred to William McKinley High School, where she would become a nationally ranked cheerleader, excel academically, and win the affection of the school's most eligible male students.
But life isn't like TV, and the thin version of me never made it out. In real life, most women's thin alter-egos never arrive. Luckily for me, I learned how to stop waiting for my "real" life to begin once I was thin. And that's just fine, because I'm better off without "thin me."
Screenplay writers, if you're reading, find an original character arc that's more entertaining and less outright insulting, K?
Millions of people will thank you for it.