I don't know of anything that actually prevents IBS once you have it, but I can tell you that taking fiber really helps. I have had IBS-D for about
15 years and had trouble believing that fiber would actually help me. But once I tried it, I found that it really helped reduce my symptoms. I take Citrucel tablets everyday without fail - two in the morning after breakfast and two in the evening after dinner. You may want to start by taking two tablets once a day and then see how many you feel you need to take to keep your symptoms under control. The fiber is also supposed to be good for IBS-C.