While Saitama's training has at least got some decent real life applications, Kae's weight loss sadly doesn't.

Kae Serinuma is the very definition of an otaku, such dedication doesn't really come with decent exercise, a good diet or sleeping habits, so she has a much larger build than most anime protagonists, that is until her favourite anime character is killed off, the shock so bad that she locks herself in her room out of sheer depression wrapping herself in her bed sheets and not even changing her clothes.
When her mother and brother finally get her out of her room after a week, they are greeted with the shock of their life as Kae has lost all the weight and bulk she used to have and for some strange reason can see better. (Kae's reaction is better)
When she does return to school, Kae becomes the prettiest girl in school.
Don't ever try this to lose weight, unless you're raised in a culture where fasting is a regular practice, not eating for that long is going to make you extremely ill, add to the fact that she likely lost alot of fluids wrapping herself in thick bed sheets while wearing lounge clothes through sweat. So starvation, dehydration and malnourished isn't the way to go.
As much as a cop out I found the ending to this series, I'm glad her personality doesn't change with her shape.
Mind you Kae's reaction to her favourite anime character dying is way tamer than any reaction to Katsuki Bakugo dying.