Monica in Friends lost around 110 lbs but I don't know how she maintained her weight after that. We have seen her working out in season 1 and 2 and that's only.
- Her primary motivation (ironically) was Chandler's hurtful comment about her weight.
Monica: What?! I mean, I didn't work this hard and-and-and lose all this weight so that I can give my flower to someone like him!
- She goes to the gym / jogs daily.
Joey: Hey Mon, I got a question for you.
Monica: Okay, for the bizillionth time, yes I see other women in the shower at the gym, and no I don't look.
- She mainly drinks diet soda
Chandler: Yeah, can I get a 3-piece, some coleslaw, some beans, and a Coke—[Monica grabs him underwater] Diet Coke.
- Her trigger food (for gaining weight) was apparently Brown Bird cookies.
Monica: All right, I’ll take one box of the mint treasures, just one, and that’s it. I-I started gaining weight after I joined the Brown Birds. Remember, how Dad bought all my boxes and I ate them all?
- Although she seems ok with other cookies (and food in general) Monica has an almost pathological fear of Brown Bird cookies.
Ross: I’ll tell you what Mon, I’ll give you the first box [of cookies] for free.
Monica: [reaches for the box, then looks at it with terror] OH GOD!!! I gotta GO!! [runs out]
- She openly acknowledges that she has a problem with food and overeating:
Monica: The fat girl inside of me really wants to go. I owe her this. I never let her eat.
Out of universe, although she consistently denies it...
I did not have anorexia, but they [the press] kept writing about it.
...the harsh reality is that maintaining a size-zero physique for nearly a decade is invariably achieved through a regimen of constant exercise, food denial and cocaine.