Why was Monica Geller overweight in her younger years?

Question

Monica Geller was shown as overweight in her early or college days in Friends. In all seasons she was shown as normal weight.

• Why was Monica Geller overweight in her early years?
• How did she become normal weight?

Answer 1

Monica was fat in her younger years because she ate too much.

• In The One Where Rachel Tells... Ross says:

  I grew up with Monica. If you didn't eat fast, you didn't eat!

• In The One With The Pediatrician we learn that Ross used to go to a therapist, because

  Monica: ... he used to have this recurring nightmare. It really freaked him out.
  Rachel: Wow, what was it?
  Monica: That I was going to eat him.

• In The One With Phoebe's Cookies it is revealed that Monica was once sent to fat camp:

  Ross: He still tells the story about how Monica tried to escape from fat camp.
  Monica: I wasn't escaping!
  Ross: Then how did you get caught in the barbed wire?
  Monica: I was trying to help out a squirrel.
  Ross: You were trying to eat it!

Monica lost the weight because of an incident during Thanksgiving 1987, when she overhears Chandler say to Ross:

I just don't want to be stuck here all night with your fat sister.

• [Watch the scene on YouTube]

  

That prompted Monica to lose weight, which she successfully managed by Thanksgiving 1988.

• [Watch the scene on YouTube]

  

Answer 2

She's never been shown overweight, but they did do a few flash backs to when she was younger and she was in a fat suite.

I think she said a few times that you would binge on things like ice cream. You weight gain came from her inability to get boys to like her.

I don't know how she lost the weight.