I heard some vegetarians gain a lot of weight?

Well i know this one girl who said she was a vegetarian for awhile. And she said she started gaining a lot of weight because she didn't take daily vitamins... Is that true? Because she also said she used to be bulimic for a long time idk if it was two years or less? But i was wondering if it might have been she just didn't eat healthy!? Her mom is also kind of large... I think it could be hereditary... I was just wondering because i am a vegetarian! Thanks :)