Irritable Bowel Syndrome or IBS is estimated to impact 20% of Americans with symptoms that include abdominal pain and loose stool, affects 20% of Americans. Dr. Gershon indicates that many doctors dismiss the severity of IBS and/or attribute it to psychoneurosis because they don't know exactly what it is. Gary M. Mawe, professor of anatomy and neurobiology at the University of Vermont, has pointed out that the GI tracts of people with IBS look essentially normal. The default assumption has been that IBS is a psychosomatic disease. It turns out that IBS, like depression, is partly a function of changes in the serotonin system: too much serotonin rather than too little. Typically, when working properly, serotonin is released into the gut and initiates an intestinal reflex. Then it is removed from the bowel by a molecule known as the serotonin transporter, or SERT, found in the cells that line the gut wall. People with IBS have insufficient amounts of SERT so they have too much serotonin floating around in the bowl, which triggers diarrhea. The excess serotonin then overwhelms the receptors in the gut, shutting them down and triggering constipation.