Panty & Stocking with Garterbelt (2010)

S1E7 Diet Syndrome

After Stocking gains a little weight, she becomes fixated on a strict diet, but her efforts prove fruitless. Instead of shedding pounds, she finds herself gaining even more and, by the following day, she has transformed into a gigantic version of herself. This surprising change is ultimately revealed to be the handiwork of a Ghost.