Reged: 12/13/04
Posts: 4490
Loc: West Orange, NJ (IBS-D)
My guess would be that orange juice has more fructose than grapefruit, lemon, or lime, so that's why you can tolerate the latter, but not the former.
As for why some of us can handle onions (like me - oh, thank you, thank you, thank you) and some of us can't (sorry): I believe IBS is actually made up of a lot of slightly different overlapping conditions or illnesses and that explains why we all have similarities, but are still all a little bit different in what we can tolerate. Someday the scientists in their shiny white labs will figure it all out and each subgroup will have it's own nifty Latin name - like "onionus non-toleratus" for you and "whole wheatius ickyus" for me.
-------------------- [Research tells us fourteen out of any ten individuals likes chocolate. - Sandra Boynton]