WebMD Medical News Source: MedicineNet.com

Not every probiotic product has proven health effects. But as a medical treatment, they're more than just the latest health fad, says University of New Mexico researcher Mohamed O. Othman, MD.

"Probiotics now have been used in many diseases, not only IBS but also ulcerative colitis and Crohn's disease and in both children and adults with lactose intolerance," Othman tells WebMD. "It is a new field, and there is a lot of investigation going on."

Help for Some, Harm for None?

"Some patients with IBS respond to treatment with probiotics. They are not all the same. Different probiotic bacteria have different effects on the intestine. So we expect it will be important to use the right probiotic for the right patient" says gastroenterologist Jay W. Marks, MD. Marks is medical and pharmacy editor for MedicineNet.com, a WebMD company.

Even so, doctors are recommending probiotics to some IBS patients. That's because the probiotics tested in clinical trials have done no harm, says probiotics researcher Eamon Quigley, MD, of the Alimentary Pharmabiotic Center at University Cork College, Ireland.

"If probiotics are as effective as we think, the great advantage is their safety," Quigley tells WebMD. "There is no evidence of any safety issue. They have the potential to be an effective first-line therapy for IBS and other bowel symptoms in a very safe manner."

Why Do Probiotics Work for IBS?

The most obvious theory is that the good bacteria displace bad bacteria. That appears to be part of the answer, says Marks. One thing that may affect some IBS patients is called small intestinal bacterial overgrowth or SIBO.

The large intestine carries a lot of bacteria -- about a billion organisms per milliliter of fluid. But the small intestine is only supposed to have 10,000 organisms per milliliter of fluid. And the small intestine is supposed to have different bacteria than the large intestine.

There's good evidence that some people with IBS have SIBO: an overgrowth of large-intestine bacteria in their small intestines. Patients who do have SIBO may benefit from probiotics. The good bacteria may displace the bad bacteria in the small intestine.

Another issue of perhaps even greater importance comes from the Quigley team's research. They find that probiotics may make subtle but important changes in the way a person's immune system works.

The immune system has built in switches that turn inflammatory immune responses on or off. This kind of immune response can be very helpful in responding to acute infection or injury. But in some people with IBS, the switch for inflammatory immune responses seems to be stuck in the "on" position. In ways that are not yet understood, probiotics turn this switch off.

"There is quite a bit of evidence that there is a change in immune function in IBS," Quigley says. "In other words, if you look in detail, you see evidence of inflammatory immune activation in IBS. Certain probiotics have potent anti-inflammatory effects that can restore the balance."

Marks is very interested in these findings, which he calls "extremely tantalizing." But he warns IBS patients that not every product sold as a probiotic is helpful. "People should not just go to a health food store and buy any probiotic on the shelf," he says. "You want to use one that has been medically studied and that has appropriate effects.”

SOURCES: Quigley, E.M. 70th annual scientific meeting, American College of Gastroenterology, Honolulu, Oct. 28-Nov. 2, 2005. Mohamed O. Othman, MD, University of New Mexico, Albuquerque. Eamon Quigley, MD, University Cork College, Ireland. Jay W. Marks, MD, medical and pharmacy editor, MedicineNet.com