The causes of IBS are complex: diet, stress, genetics, anatomy…. Some sufferers have bloating, gas and diarrhea, others have bloating and constipation, still others vacillate back and forth.
One possible cause is poorly absorbed carbohydrates called FODMAPS (fermentable oligo-, di- and mono-saccharides and Polyols). These are high in animal milks, some fruits and vegetables, beans, and some grains–all very healthy foods, as well as sugar free gums and candies Most of us handle FODMAPs very well; but, In SOME people, when these reach the large intestine, they cause bloating and discomfort and either diarrhea or constipation.
The way to figure out if FODMAPs are your problem is to go on a very low FODMAP diet for 2 or more weeks and see if symptoms improve. If they do, then you would challenge each type of FODMAP, one at a time, over a week or more each. The goal is to find out how much of each group you can tolerate without symptoms. You do not want to limit your eating more than necessary.
It is best if you work with a dietitian-nutritionist who is experienced in working with IBS to make sure that you are meeting all your nutrient needs while eliminating FODMAPs, and that you are doing the challenges in a way that you can pinpoint which carbohydrates you have problems with.
You can find out more about IBS and FODMAP sensitivity just by researching on the internet. Two great books that give detailed information about IBS and FODMAPs:
IBS, Free at Last, Change your Carbs, Change Your Life by Patsy Catsos, MS, RD, LD, Pond Cove Press, ©2012, ISBN: 0-9820635-2-0.
The Complete Low-FODMAP Diet, A Revolutionary Plan for Managing IBS and Other Digestive Disorders by Sue Shepherd, PhD and Peter Gibson MD, The Experiment, ©2013, ISBN: 978-1-61519-080-5