Your parents (and doctor) need to be aware of, and understand, the dietary restrictions of IBS. Have your parents log on to this site and read through the IBS diet section. Get the book The First Year: IBS (order from this site or get a copy at your library) and have your parents read it, then take it to your doctor and show him/her the dietary chapter. Show them the dietary articles in the IBS research library here on the boards, that prove fats are a tremendous trigger for IBS.
It is impossible to gain weight by eating foods that make you physically ill. While your parents cannot force feed you, they can cause you such tremendous mental distress about this issue that you end up in even worse health, and they need to realize this. Simply putting you in a position where you are constantly arguing with them about what you can and cannot eat is surely not helping you - can they log on to this message board and see these posts?
There is also some info in the diet FAQ on gaining weight here Weight Gain
Best, Heather
-------------------- Heather is the Administrator of the IBS Message Boards. She is the author of Eating for IBS and The First Year: IBS, and the CEO of Heather's Tummy Care. Join her IBS Newsletter. Meet Heather on Facebook!