Usually if you weigh yourself in the morning after you poop (gross, but legit) that's your actual weight, and before you go to bed you'll weigh that plus all the food you ate that day. Even water has weight (hence the term 'water weight'), and some people lose that weight a lot slower than others. This can be due to a lot of things, and ironically one of the best ways to lose it is to sweat it out. (Which while this probably wasn't thought of in the story would actually be a great reason why Jiwon goes so hard in the gym.)
Sorry!!! I used to be really heavy and put a lot of research into stuff like this. ( >.< )
I drink lots of water and my doctor says it's the reason why I can't gain weight so I stopped drinking water that much. Flavored drinks the best! I really want to gain weight because I'm underweight. :(
Wait, how can you gain weight with just drinking water?
I feel ya DG, it's hard for me to gain weight too :(