Irritable bowel syndrome is not "all in the head," as has been commonly thought. In a review of the literature, Michael Camilleri, M.D., a Mayo Clinic gastroenterologist and author of an article in the New England Journal of Medicine, describes a renaissance in the understanding of the condition, also known as IBS. He dismisses the notion that symptoms are specific to a single cause, and says symptoms are indications of several disturbed motor and sensory processes.

Irritable bowel syndrome is common, affecting 10 to 20 percent of the population in developed countries. IBS is not a disease, but rather a group of symptoms that occur together. The most common symptoms are cramping, abdominal pain, bloating, gas, diarrhea and constipation.

"Our goal is a better understanding of the mechanisms behind this syndrome. That way, we can foster individualized, specific treatment for patients with IBS," Dr. Camilleri says.

Why patients develop IBS is not clear. Psychological factors and genetic predisposition play a part in IBS, but Dr. Camilleri points to a variety of underlying irritants that disturb gastrointestinal functions and contribute to IBS symptoms. Examples include digesting certain food, prior gastroenteritis, the patient's gut flora, and bile acids and fatty acids (involved in digestion of food) arriving in the colon.

"If we can identify these irritants in the individual patient, we have the opportunity to prevent or reverse symptoms," Dr. Camilleri says.

IBS is typically diagnosed after a patient has recurrent abdominal pain or discomfort at least three days per month, in the previous three months, combined with a change in the frequency of bowel movements or a change in stool's appearance.

IBS can occur at any age, but often begins in the teens or early adulthood. It is twice as common in women as in men. Studies have shown that people who have a first-degree relative with IBS are at increased risk.

IBS may be a lifelong condition. For some people, symptoms are disabling and reduce the ability to work, travel and attend social events. Treatment often helps. Common treatments include fiber supplements, anti-diarrheal medications, eliminating high-gas foods, anticholinergic medications, antidepressants, antibiotics and counseling.

Dr. Camilleri is the Atherton and Winifred W. Bean Professor at Mayo Clinic. Ethics disclosures: Dr. Camilleri reports receiving consulting fees from Takeda Pharmaceuticals USA, Albany Molecular Research, BioKier, Theravance, Alkermes, ARYx Therapeutics, AstraZeneca, Domain Therapeutics, Ironwood Pharmaceuticals, Tranzyme, and NPS Pharmaceuticals; receiving grant support from Rose Pharma, Albireo, Tsumura, Second Genome, SK Life Science, Salix Pharmaceuticals, and Rhythm through his institution; being a co-inventor of a patent related to enteric delivery of chenodeoxycholic acid for constipation; and receiving royalties from EnteroMedics for licensed technology related to vagal-stimulation treatment of obesity.