I also lost a lot of weight, dropping from 125 Ibs. to 101, mostly because of my many food sensitivities. During a severe relapse, I normally can only stand 7-Up and very small portions of soft-cooked white rice; that's when my weight really plummets! During periods of stability and following my very strict diet (almost no fat, no gluten, no coarse fibre, nothing acidic, etc.) my weight normalizes because I binge the on foods I *can* tolerate, in my case, bananas. So to those of you who are underweight: have lots of the foods you are able to eat; this will help you during your next flare-up! Boost and Ensure, if you can tolerate them, provide extra calories, protein, and essential vitamins and minerals. -To Shadowz: Change doctors if you can! I also had an uncaring, rather ignorant doctor when I was first diagnosed with IBS. Switching to a new doctor who was more knowledgeable and concerned did wonders for me, at least on an emotional level.