Maybe a character doesn't like his current shape and decides he's going to drop those pesky pounds if it kills him. Maybe he meets an unusual stranger on the street with slimming abilities. The point is, he loses weight (or at least takes steps to do so).
And everything goes straight downhill.
This trope is for works in which weight loss goes horribly wrong (or, even worse, horribly right). Maybe the characters lose too much weight and are in danger of disappearing altogether. Maybe they unwittingly sign themselves up for a weight-loss service with overly restrictive (read: lethal) penalties. Maybe the diet is magical and requires the sacrificing of children. Really nasty examples may overlap with Body Horror, and self-inflicted magical ones might cross over with Be Careful What You Wish For.
Compare Fashion Hurts, for other ways in which the effort to maintain appearance can be painful and/or harmful, and Dead Weight and Fattening the Victim for other cases in which weight is associated with horror.
This trope appears in the following works:
- In X-Men, whoever is chosen as Famine in Apocalypse's Horsemen can cause people to become emaciated by touching them.
- In an issue of the Italian horror comic Dylan Dog a demon is trying to do good, but not being familiar with the concept he keeps bungling up, with horrific consequences. For one of his "good deeds" he sends some magic diet pills to a Fat Girl who wishes to be thin. She loses weight near-instantly and gets the figure of a supermodel, but when she wakes up the following day she's wasted to little more than a skeleton. And that's when the flesh-eating bugs who've been "slimming her down" from the inside break through her skin and devour the rest of her.
- "Fat Farm", by Orson Scott Card. A very rich, very fat man uses a service to copy himself into a healthy body. Unfortunately, he didn't check to see what happens to the original. Turns out it becomes the property of the cloning company... and they're not very humane with their human resources.
- The Monkey Treatment, by George R.R. Martin. A fat guy who's tried every diet inadvertently signs up for the monkey treatment, in which an invisible magic monkey sits on his back and snatches away all his food before he can eat it. At first, this works great. But then he realizes that for every pound he loses, the monkey gains one, and as it grows bigger its power and malevolence increase as well.
- In "The Iron Chancellor" by Robert Silverberg, a family purchases a Robot Maid to oversee their diet. It does its job a bit too well, so they try to adjust its programming and short something out.
- Thinner, by Stephen King: A fat lawyer is cursed by a gypsy to lose weight. As in, all of it.
- H. G. Wells ' 'The Truth About Pyecraft'': A very fat man takes a potion to lose weight. And he does — but he doesn't actually become thinner. He just weighs less until he's floating up into the air like a large balloon.
- The Goosebumps book "Say Cheese and Die Again!" has this trope both Played Straight and Inverted. The male protagonist and his female friend both fall victim to the evil camera, with a picture showing him as morbidly obese, and his female friend as a skeleton. He starts to gain weight involuntarily, she starts to lose it.
- In the Doctor Who episode "Partners in Crime", Adipose Industries produces a special pill that makes your fat walk away: literally, it turns body fat into a little creature called "adipose" that looks like an anthropomorphic marshmallow, which then leaves the host's body. Consuming too many adipose pills may destroy a human's body completely.
- One of The 4400 comes back to be accosted by the gangster he owed money to before he was abducted. The gangster takes a bite of the sandwich the man was eating and subsequently loses a lot of weight. It turns out the man's ability is to create an enzyme in his saliva which accelerates a person's metabolism. The gangster then gets his wife to eat something the man was eating and she too loses a lot of weight. However, it later turns out that the enzyme causes their metabolism to speed up to the point where they're burning calories faster than they can take them in. The gangster and his wife both end up starving to death despite eating a big meal.
- In the Smallville episode "Craving", bullied, overweight teen Jodi takes Kryptonite vegetable shakes in order to lose weight. The pounds melt off and she starts to get positive attention from her classmates. She is overjoyed until she realizes the weight loss will not stop. She eats everything in sight trying to keep weight on. When regular food no longer works, she moves to freshly killed raw meat and then to sucking all the fat and marrow out of other humans, the only thing that seems to sate the hunger. Unfortunately, it also kills them.
- In the French comic Melusine, the titular witch hypnotizes an obese man into losing weight. She drops by his home a while later to see how he's doing... and finds that his wife is hiding his toolbox, he's cut off his legs and is trying to bite off his fingers while mumbling a Madness Mantra about losing weight.
- Garfield has had nightmares of these, such as slipping down a sewer drain or being reduced to just a skeleton. He would then proceed to gorge on lasagna to avoid letting these nightmares come true.
- A Played for Laughs example is Bob from Tekken series, an acrofatic character that likes his overweight status. However, in his Tekken 6 ending, after all the effort to win the King of Iron Fist Tournament, he suddenly lost 150 pounds, becoming slim, which was a shock for him. Bob thinks his weight loss was a curse to him, losing also his strength and speed gained with the training that made him fat. First being a cameo, later this becomes a separate character in Tag Tournament 2 as "Slim Bob".
- NOT played for laughs in Red Dead Redemption II. The player is treated to gradually watching the tall, broad-shouldered and tough-as-nails cowboy Arthur Morgan gradually waste away to nothing from tuberculosis, a bacterial infection that was a death sentence for anyone who contracted it in 1899. It's actually possible for him to become more underweight than the game normally allows.
- Used in an episode of Freaky Stories. A woman buys a new mysterious diet pill in preparation for a beauty contest, on the condition that she must not drink water for the duration of the diet. The diet pill was actually filled with several tiny sponges, and when she breaks and drinks gallons of water, they cause her to bloat uncontrollably.