"The Diet Syndrome" is the 7th segment of Panty & Stocking with Garterbelt. It aired during the fourth episode on October 22, 2010 in Japanese, and on June 19, 2012 in English.
Stocking finds herself gaining weight and goes on an intense diet, only to keep getting fatter until she balloons into a giant.
The episode starts with a narrator, who explains how girls in Daten City often go on extreme diets in order to maintain overly slim figures, sometimes even leading to their own deaths. The setting changes to the church's living room, where Stocking is seen eating a white cake-like roll. She assures the cake is delicious and completely worth the 2-hour waiting line.
Panty arrives from her daily exercise routine, and tells Stocking that if she keeps eating all those sweets she is going to get as fat as a whale. Stocking reassures her that she never gains weight and even makes fun of Panty for having to exercise in order to mantain her figure. While taking a bath, Stocking comments on how she should try a Belgian chocolate featured on her magazine, but upon looking at herself in the mirror, she notices her waist was getting fatter. The next morning, Stocking wakes up early in order to jog in secret and returns to check on her weight again. She finds out that she didn't lose any weight at all, but in fact she had gained a few pounds.
Panty came to the living room carrying a bunch of sweets someone gifted her and tells Stocking she could have them. To Panty's surprise, Stocking denies them, so Panty decides to give them to Chuck instead. Stocking tries to stop her, but is too late as Chuck eats them all. Panty gets suspicious and asks Stocking if she is on a diet. Stocking denies it, to where Panty lifts her blouse and finds a vibrating belt for weight loss. Stocking goes mad and escapes to the elevators with Chuck, where she starts punching him for eating her cake.
The following few days, Stocking exercises like mad and goes on a diet, which consists of only eating food with few calories. Meanwhile, Panty goes to Whity-White and buys a bunch of cake-rolls in order to give them to Stocking, but is shocked to find Stocking strange and zombie-looking when she comes back, where she turns down the cakes. Stocking checks her weight once again, and discovers, to her horror, despite her efforts and sunken in cheeks she has grown even fatter and has a sizable stomach. Pissed off and seeing all her efforts are worthless anyway, Stocking devours all the cakes, with Panty standing back in disgust and worry.
That morning, Stocking balloons into a spherical giant and destroys part of the church. Panty, upon seeing Stocking, laughs at her while Stocking says that she's given up losing weight because it's too much effort, and Chuck is suddenly stricken by lightning. Garterbelt tells both Anarchy sisters that most of the women in Daten City are getting obese, and that the cause is Whity-White's cake-roll, stating that it was a ghost's doing. Stocking, completely enraged, tells Panty it is payback time, and both angels go to Whity-White's factory, with Stocking rolling the way there with Panty on top (crushing a number of cars along the way). It turns out the ghost behind it is trying to make everyone in Daten City fat because she didn't want to go on a diet herself. The ghost shoots at Panty a white creamy substance that would cause her to become fatter, but is saved by Stocking, who starts eating it. Stocking tries transforming her stocking into Stripe I, but it failed since her stockings were too stretched out. The ghost attempts to escape, until Panty kills it, as it leaves 4 Heaven Coins behind. Stocking returns back to her normal figure and ends up eating sweets again like nothing ever happened.
During the scene where Panty is laughing at Stocking while her massive frame is stuck in the tower, In the original script Stocking says it is to much effort to stay thin. In the english dub she threatens to eat her sister in a breakfast taco.