IBS Tales Home
Header Image

IBS Tales Home > About IBS > Causes of IBS Part One

causes of ibs - part one

There are a number of different theories regarding the cause of IBS, and I have outlined the main theories below. Although I've separated them out into different categories for easy reading, in reality there may well be intrinsic links between the theories. I've included information from a number of clinical studies on this page. Whenever a clinical study is mentioned, it's presented as a bullet point, and in each case I give the title of the study, the names of the researchers, the name of the journal that published the study, and a link to a Pubmed summary of the study.

Brain-gut dysfunction

Although the understanding of what causes IBS is still in its infancy, one of the things that most experts agree on is that IBS patients suffer from something called 'visceral sensitivity'. This is basically a fancy term for the fact that IBS sufferers have more sensitive intestines than healthy people, and so contractions of the intestines that wouldn't bother most people are felt by IBS patients as painful - and contractions that are particularly severe, involving diarrhea for example, can be agonizing.

This heightened sensitivity is an accepted part of IBS theory because it has been shown in several clinical studies that IBS sufferers actually process gut stimuli in a different way to non-sufferers, leaving us with a lower threshold for pain.

This is categorically not an invitation for lots of people to start beating IBS sufferers over the head with a big stick saying 'Yes, I knew you were all just wimps. Get a grip'. We don't, of course, have any control over our pain thresholds, and indeed the studies which show that we process gut stimuli in a different way are proof of this - I don't know about you but I don't have much conscious control over my anterior cingulate cortex.


What this aberrant brain activation shows is that we IBS people are processing our gut stimuli in a different way to non-sufferers. This is pretty interesting stuff, but what it doesn't tell us is what is causing the heightened sensitivity. So, researchers have started to investigate what is called the 'brain-gut dysfunction', and indeed some of the possible causes of IBS listed below are being examined for the effect they could have on the brain-gut axis.

Here's a paper which sums up the possible role of the brain-gut axis in IBS (the word 'pathogenesis' just means the origination of a disorder, ie: the cause).


Low-grade inflammation

One of the reasons why IBS has been considered a rather mysterious disorder in the past is because tests such as colonoscopies and blood tests would always come back negative, and no visible sign of a problem could be found. This was in direct contrast with other disorders such as inflammatory bowel disease, where the inflammation of the intestines could be seen during a colonoscopy.

Recently, however, studies have begun to find that although there is no inflammation present that is visible to the naked eye, IBS patients may display low-grade inflammation which can be detected through biopsies and microscopic studies.


Mast cells

Mast cells are another area where physical differences have been found between IBS sufferers and healthy people. Mast cells have a number of roles within the body, including influencing smooth muscle function - and so mast cells could be implicated in the visceral sensitivity which characterizes IBS.


Bacterial causes

There are many IBS sufferers who can trace the onset of their symptoms back to the use of antibiotics or a stomach upset, and one bacterial theory of IBS suggests that the symptoms are the results of an imbalance between the 'good' and 'bad' bacteria within the gut. This theory is supported by studies that have shown the strong negative influence that antibiotics can have on bowel symptoms, as well as the positive influence that probiotics can have.


Another bacterial theory suggests that IBS is not caused by an imbalance between good and bad bacteria, but by an overgrowth of bacteria in the wrong place within the gut. Dr Mark Pimentel of Cedars-Sinai Medical Center has pioneered the theory of Small Intestinal Bacterial Overgrowth (SIBO), which states that IBS symptoms are caused by gas-producing bacteria within the small intestine. By testing patients for the presence of bacteria with a simple breath test, and then treating these bacteria with antibiotics and diet therapy, the IBS symptoms can be eliminated.

Clinical trials have already shown good results for patients who follow this approach. One of the most interesting aspects of this theory is that it offers a possible explanation for fact that some IBS sufferers are diarrhea-predominant, and some are constipation-predominant (various types of bacteria emit different gases and therefore cause different symptoms).

Go to Causes of IBS (Part Two)