Recent work has shown that the composition and location of gut bacteria can cause symptoms which are experienced by IBS patients. For example, if you have bacteria in the small bowel (SIBO – small intestinal bacterial overgrowth), they will begin to ferment foods before your body has had chance to digest and absorb the nutrients.
This produces gas and acids (short chain fatty acids) within the small bowel which can lead to changes in sensitivity and motility. As the small bowel is not designed to cope with this fermentation it can lead to symptoms of nausea, bloating, pain, indigestion, heartburn, belching, fatigue and headache. As similar effects will be felt almost regardless of whatever foods you eat (healthy or not!) this can be very confusing for patients.
If the problem is with the composition of gut bacteria within the colon, this means that normal fermentation can become excessive or produce undesirable by-products which effect factors such as gut motility and sensation as well as make you feel generally unwell. It has recently been conceived that suffering from a previous gastrointestinal infection can change the gut microbiota and make people more susceptible to SIBO.