As far as I'm concerned, it's not a TV series, but the movie "Little Fat Revolution". I also like her name Hyeon-jin Lee because of this play.

The chubby revolution advocates "the happy life of fat people" in an era when everyone is keen on slimming. The heroine in the film is a top model. In order to pursue her sweetheart, she catered to each other's aesthetic orientation and transformed herself into a fat girl in a short time.