The all-too-descriptive term “irritable bowel syndrome” (IBS) is characterized by abdominal pain and cramping, changes in bowel movements, and anxiety/depression disorders.
IBS ranks as the most common gastrointestinal complaint in the United States, with about one in six Americans suffering at least some IBS symptoms (see our “IBS basics” sidebar, below).
No definitive cause(s) of IBS has emerged to date, but researchers are beginning to uncover some prime suspects … with bacterial infections leading the pack.
The infection hypothesis of IBS appears to explain many cases … and new findings lend more weight to that idea.
The disease ranges from periodic discomfort to serious suffering, often begins in adolescence or early adulthood, and is more common in women.
It is not the same thing as inflammatory bowel disease (IBD) – a term that covers Crohn's disease and ulcerative colitis.
Doctors commonly categorize patients with “constipation predominant” IBS, “diarrhea-predominant” IBS, or with an alternating pattern of the two.
Patients with the alternating pattern are more likely to suffer abdominal pain or cramps, excess gas or bloating, and visible abdominal distension.
The colon links directly to the brain through the nervous system, and IBS often worsens in times of stress.
This is because nerves in the intestines react to stress signals by making gut muscles contract, causing pain and bowel problems.
The good news would seem to be that bacterial infection is one IBS-inducer we can attack – and help prevent, in food-service settings – with increasing efficacy as research proceeds.
Infection theory of IBS gets a big boost
Sometimes, IBS appears after an intestinal infection.
And some evidence – breath tests finding bacteria-produced methane, and healing responses to antibiotics – indicates that bacteria play a role in the disease.
Last year, researchers from Cedars-Sinai Medical Center in Los Angeles reported that in clinical trials, a targeted antibiotic (rifaximin) provided effective, long-lasting relief of IBS symptoms (CSMC 2010).
They said this was the first drug treatment for IBS to relieve symptoms while being administered and for at least 10 weeks after patients stopped the drug. (They weren't followed longer than that, oddly.)
Now, the same team of Cedars-Sinai researchers report two advances in the understanding of Irritable Bowel Syndrome.
One study provides further evidence that IBS is linked to an overgrowth of bacteria in the gut.
And the Cedars-Sinai team's separate analysis of health data reveals a likely causal link between food poisoning bacteria and many cases of IBS … with military personnel running a much higher risk.
Gut bacteria studies bolsters infection theory
Along with researchers in Athens, Greece, scientists from California's Cedars-Sinai looked at small bowel cultures to confirm the presence of small intestinal bacterial overgrowth (SIBO) in patients with IBS.
In this study, 320 patients had an endoscopy of their upper GI tract, from which a small bowel culture was cultivated.
The participants with IBS were almost four times as likely to show bacterial overgrowth in the small intestine, compared to people free of IBS (37.5 percent versus 10 percent).
The overgrowth was more prevalent in those with the diarrhea-predominant version of the disease. Researchers also found more different kinds of bacteria in IBS patients, versus people free of IBS.
“The better we understand this disease, which affects millions of Americans, the more tools we will have for fighting it,” said Mark Pimentel, MD, director of the Cedars-Sinai GI Motility Program and a primary investigator on both studies (CSMC 2011).
“Patients with this condition suffer serious quality of life issues. It's a disease that is frequently misunderstood and difficult for people to talk about, but it's important for the medical community to understand the causes of the disease so we can develop the most effective treatments possible.” (CSMC 2011)
Mathematical analysis links common food-poisoning bugs to IBS
In a separate study, the Cedars-Sinai team used a mathematical model to analyze data from the Centers for Disease Control and other research studies.
The Cedars-Sinai researchers concluded that food poisoning bacteria may account for the majority of irritable bowel syndrome cases.
Further, the model predicted higher rates of IBS among military personnel eating in mess halls … as has been seen in other cafeteria-fed “institutional” populations.
The model projects that nine percent of people institutional settings, who also have a genetic predisposition for IBS, will contract it after 10 years.
However, among deployed military and certain other high risk groups, nine percent would develop IBS within a mere six months.
As Dr. Pimentel said, “… this study reminds us that we need to pay greater attention to the dietary woes and digestive upsets that long have been the subject of wry discussion among overseas forces”. (CSMC 2011)
Let's hope the Defense Department rapidly funds more research, and in the meantime employs tougher sanitation and food service measures to curb infection and IBS rates.
Cedars-Sinai Medical Center (CSMC 2011). Cedars-Sinai Research Deepens Understanding Of Most Common Gastrointestinal Disorder In U.S., Linking It To Bacterial Overgrowth, Food Poisoning. May 11, 2011. Accessed at http://www.eurekalert.org/pub_releases/2011-05/cmc-crd051011.php
Cedars-Sinai Medical Center (CSMC 2010). Cedars-Sinai Research Shows Antibiotic Prevents IBS Symptoms For Weeks After Final Dose: Results confirm earlier Cedars-Sinai studies showing effectiveness of rifaximin against chronic IBS. May 3, 2010. Accessed at
Kunkel D, Basseri RJ, Makhani MD, Chong K, Chang C, Pimentel M. Methane on Breath Testing Is Associated with Constipation: A Systematic Review and Meta-analysis. Dig Dis Sci. 2011 Feb 1. [Epub ahead of print]
Pimentel M, Morales W, Chua K, Barlow G, Weitsman S, Kim G, Amichai MM, Pokkunuri V, Rook E, Mathur R, Marsh Z. Effects of Rifaximin Treatment and Retreatment in Nonconstipated IBS Subjects. Dig Dis Sci. 2011 May 11. [Epub ahead of print]
Pimentel M. Evaluating a bacterial hypothesis in IBS using a modification of Koch's postulates: part 1. Am J Gastroenterol. 2010 Apr;105(4):718-21.
Shah ED et al. Mathematical Modeling Estimates the Impact of Acute Gastroenteritis On the Development of IBS in the U.S. Digestive Disease Week, May 7-10, 2011, Chicago. Accessed at http://ddw.apprisor.net/DDW_PRES.cfm?id=3949
Youn YH, Park JS, Jahng JH, Lim HC, Kim JH, Pimentel M, Park H, Lee SI. Relationships Among the Lactulose Breath Test, Intestinal Gas Volume, and Gastrointestinal Symptoms in Patients with Irritable Bowel Syndrome. Dig Dis Sci. 2011 Jan 15. [Epub ahead of print]