At around 4:40 in the 1st episode of The Quintessential Quintuplets, Uesugi said that eating too much would make Itsuki gain weight, and then Itsuki get pissed.
Isn't gaining weight as a teenage very normal? That's how your body develops. Why was Itsuki annoyed?
Another example about gaining weight is from Lucky Start. At around 9:30 in Episode 22, Konata said to Kagami, 'you will gain weight'. Then Kagami got sad.
What's so bad about gaining weight in Japan?