Irritable bowel symptom, or IBS,  is a common functional disorder of the gastrointestinal tract characterized by abdominal symptoms such as abdominal pain and discomfort, bloating and change of bowel habits leading to either diarrhea or constipation. The exact cause of IBS is not clear, but stress, gastrointerstinal infections or antibiotics use are often triggers of the onset of IBS symptoms. One theory gaining ground is that it may be due to a shift in the balance of billions of bacteria which normally inhabit our intestine, towards those bacteria that produce excess gas and could possibly initiate an inflammatory response. The treatments of IBS include anti-diarrheals for diarrhea predominant IBS, stool softeners for constipation-predominant IBS, and antispasmodics for pain relief. However, these medications seem to only be able to provide temporary relief.

In one study, 52 people diagnosed with IBS were divided into two groups. One group was supplemented daily for 8 weeks with probiotic containing 25 billion live bacteria per daily dose. The second group received a placebo capsule. None of the participants knew if they were taking the probiotic or the placebo capsule. The following IBS symptoms were assessed every two weeks during the study period an again at 10 weeks. Two weeks after taking the probiotics, participants noticed decreased in days with pain, decreased in abdominal pain, decreased bloating, and improved quality of life.

The study suggested that supplementing large number of these beneficial bacteria may have the effect of "crowding" out the bad bacteria in the gut thereby helping to reduce gas production and pain.

Williams E.A., et al. Clinical trial: a multi-strain probiotic preparation significantly reduces symptoms of irritable bowel syndrome in a double-blind placebo-controlled study. Aliment Pharmacol Ther 2009:29:27-103