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

causes of ibs - part two

Food intolerance

Although most IBS sufferers believe that there are specific foods, or specific groups of foods, which exacerbate their symptoms, there have been relatively few research studies looking at food intolerance as a cause of IBS. However, there are several studies which show that food may be a real factor in the development of IBS, and these studies are described below.

As well as these studies, the success of diets such as Heather Van Vorous' Eating for IBS program lend anecdotal support to the idea that food can at the very least strongly influence IBS symptoms. The Natural Health Advisory Service in the UK has been treating IBS patients for many years based on an elimination diet program, and companies such as York Allergy offer blood tests for food-related antibodies that some sufferers have found helpful. There are also, unfortunately, companies which offer food intolerance tests which are based on little or no science at all, such as hair tests, and these should be avoided.

  • Food allergy and irritable bowel syndrome Current Opinion in Gastroenterology 2005

    'Recent clinical and experimental studies imply that dietary factors may be more important in the pathogenesis of irritable bowel syndrome than was earlier anticipated.

    Food elimination based on serum immunoglobulin G antibodies in irritable bowel syndrome has been found to result in a significant decrease in symptoms, compared with diets in which dietary restrictions are not guided by those antibodies.

    Both numbers of mast cells and their mediators have been shown to be increased in intestinal mucosa in patients with irritable bowel syndrome, especially in the close proximity of intestinal nerves. Animal studies have demonstrated that this increase in intestinal mast cell density could be a consequence of local hypersensitivity to food antigens.

    Conclusion: Dietary factors may significantly contribute to the pathophysiology of irritable bowel syndrome. Elimination diets based on the detection of local food hypersensitivity may offer a treatment option for irritable bowel syndrome patients in the future. Pubmed article: Kalliomäki MA

  • Food elimination based on IgG antibodies in irritable bowel syndrome: a randomised controlled trial Gut 2004

    Researchers used the ELISA (enzyme linked immunosorbent assay) test, which sufferers can access through York Tests or Cambridge Nutritional Science, to determine IBS sufferers had high levels of IgG antibodies to foods that were influencing their symptoms.

    A total of 150 IBS sufferers were placed on either a diet based on their ELISA test scores, or on a sham diet which excluded foods, but not those which they had shown reactions to in the test. After 12 weeks, patients who had used the ELISA-guided diet had a 10% greater reduction in their symptoms than patients on the sham diet, and patients who had been strictly complying with their diet had a 26% greater reduction in symptoms than the control group.

    Conclusion: Food elimination based on IgG antibodies may be effective in reducing IBS symptoms and is worthy of further biomedical research. Pubmed article: Atkinson W, Sheldon TA, Shaath N, Whorwell PJ


  • Food intolerance: a major factor in the pathogenesis of irritable bowel syndrome The Lancet 1982

    Specific foods were found to provoke symptoms of irritable bowel syndrome (IBS) in 14 of 21 patients. In 6 patients who were challenged double blind the food intolerance was confirmed. No difference was detected in changes in plasma glucose, histamine, immune complexes, hematocrit, eosinophil count, or breath hydrogen excretion produced after challenge or control foods. Rectal prostaglandin E2 (PGE2), however, increased significantly, and in a further 5 patients rectal PGE2 correlated with wet fecal weight.

    Conclusion: Food intolerance associated with prostaglandin production is an important factor in the pathogenesis of IBS. Pubmed article: Jones VA, McLaughlan P, Shorthouse M, Workman E, Hunter JO

Serotonin levels

Serotonin is a chemical neurotransmitter, which means that it transmits nerve impulses. It is most famous as being involved in depression, because changes in the level of serotonin in the brain can affect our moods. However, serotonin is also found in the gut, where it affects the rate of intestinal motility. Abnormal levels of serotonin in the gut can result in constipation or diarrhea, depending on whether there is too much serotonin (diarrhea) or too little (constipation).

This idea is supported by the relative success of the drugs Lotronex and Zelnorm, both of which work on serotonin in the gut. Lotronex blocks the action of serotonin to decrease motility and so reduce diarrhea, and Zelnorm increases the action of serotonin to increase motility and reduce constipation.

Different types of serotonin are known by what are called 'receptor subtypes', which are identified by a code which starts with '5-HT', or 5-hydroxytryptamine. The serotonin which is found in the intestines is mainly of the 5-HT3 and 5-HT4 subtypes. Lotronex targets 5-HT3 subtypes, while Zelnorm targets 5-HT4 subtypes.

Anti-depressants can also affect the 5-HT3 and 5-HT4 subtypes, and this could explain why they can reduce IBS symptoms in some patients.


Psychological and psychiatric problems

'And the current wisdom is that most ulcers are caused by a bacterium, not by hidden anger at one's mother.'

The first thing to say here is that IBS is NOT a psychological or psychiatric disorder - it is not 'all in your head'. If you want proof of this just get hold of a copy of my book Sophie's Story and see what the leading gastrointestinal institutions in the world say about the all in your head issue.

Having said that, there's no doubt that things like stress and anxiety can exacerbate symptoms of IBS, mainly due to the brain-gut connection already described. But that still doesn't make IBS a psychological problem, it just means that in IBS sufferers the interaction between our brains and our guts is abnormal.

However, for years and years IBS patients were told that their symptoms were purely psychological, and I think it's important to understand why. I think that there are two main reasons. The first reason is that IBS sufferers would undergo tests such as colonoscopies and blood tests and the results would come back completely normal, as opposed to conditions such as Crohn's disease where physical abnormalities could be seen. Because of the apparent absence of physical problems, IBS was assumed to be psychological.

This assumption was, of course, flawed. If you look for physical signs of diabetes using a colonoscopy you're not going to find much, but that's not because the patient doesn't have diabetes, it's just because you're doing the wrong test. Just because IBS patients don't have visible problems doesn't mean that their problems aren't physical, it just means that the doctors don't really know what they're looking for yet.

The second reason for a psychological assumption was that IBS patients would often have obvious signs of mental instability - they would be depressed, or anxious, or burst into tears when describing their symptoms. Therefore, it was assumed that the mental and emotional problems were causing the IBS symptoms themselves.

This assumption is even more flawed the previous one. Firstly, coincidence is not causality. Just because IBS sufferers often display symptoms of depression and anxiety does not mean that the depression or anxiety is causing the IBS.

Secondly, if there were ever a group of people that you might expect to suffer from depression, it would be IBS patients. We have to put up with years of stabbing pain, urgent diarrhea, terrible constipation, and little sympathy. If you put a human being through years of pain, they sometimes get depressed; if you give them diarrhea so urgent that they only have 10 seconds to find a bathroom, they sometimes get anxious. Where's the causality there?

Yes, emotional and mental problems, and basic stress, can exacerbate our symptoms - but so can certain foods, drinks, and other kinds of stimuli. And yes, maybe the guts of IBS sufferers are more sensitive to emotions and mental health issues, but that's a problem caused by the brain-gut axis, not by the mental problems themselves.

If we're going to decide that something like stress or anxiety is the cause of IBS, we might as well say that stress is the cause of asthma while we're at it. After all, lots of people are more prone to asthma attacks when they're stressed. So that's obviously the cause, right? Well...obviously not.


Research studies have shown that psychological problems are more common in IBS sufferers than in people who suffer from other gastrointestinal problems. This, of course, may be due to the fact that people with Crohn's disease or colitis get treated as if they have a 'proper' medical condition, whereas IBS sufferers are told to go home and stop being such a worry-wart.

The important thing to note, though, is that studies have also shown that people with IBS who do not seek medical treatment have similar rates of psychological problems to the population at large. If IBS is caused by psychological problems then how do we explain all these head-healthy people with gut-wrenching bowels?


Let's take a look at what some clinical studies have shown about the psychology of IBS.

  • Psychometric scores and persistence of irritable bowel after infectious diarrhea The Lancet 1996

    This study still occasionally surfaces as a justification for the psychological explanation. The authors recruited 75 patients who had suffered from acute gastroenteritis and asked them to complete psychometric tests. Of the 75 patients, 20 were still suffering from IBS symptoms after six months had passed.

    Conclusion: The authors found that the patients who suffered from prolonged IBS were more likely to have higher scores for anxiety, depression, somatization and neurotic traits than patients who did not develop IBS. Pubmed article: Gwee KA, Graham JC, McKendrick MW, Collins SM, Marshall JS, Walters SJ, Read NW

    I would question how much weight this study really gives to a psychological explanation of IBS. All it really tells us is that people with anxiety or depression may be more prone to IBS than other people - and this could be for any number of reasons, including the general health of the patients, the propensity of disorders such as depression to cause bowel problems anyway, and the influence of psychological problems on complex aspects of the brain-gut axis.

  • Incidence and epidemiology of irritable bowel syndrome after a large waterborne outbreak of bacterial dysentery Gastroenterology 2006

    This study, and others, showed a clear link between IBS and gastroenteritis, which can hardly be ascribed to psychological factors. It examined an outbreak of E. coli in Walkerton, Ontario in May 2000, which was caused by contaminated water. Seven Walkerton residents were killed by the outbreak, and doctors followed the health of 2069 of the remaining residents.

    The 2069 people were only eligible for the study if they had no previous history of IBS. They were split into three group: people who had not suffered from gastroenteritis following the water contamination, people who had self-reported gastroenterities, and people who had clinically suspected gastroenteritis.

    Conclusion: The researchers found that 10.1% of the control group met the Rome Criteria for the diagnosis of IBS, whereas 36.2% of people with clinically suspected gastroenteritis met the Rome Criteria. In other words, IBS was more than three times as common among people who had suffered from gastroenteritis. Pubmed article: Marshall JK, Thabane M, Garg AX, Clark WF, Salvadori M, Collins SM; Walkerton Health Study Investigators

    In my view, the Walkerton study shows a very clear link between IBS and gastrointestinal infection, and this is obviously not a link that needs a psychological component to explain its existence.


Let's look at one final myth about the psychological side of IBS, and that's the idea that it is somehow caused by a history of sexual abuse. This is a myth that is heard less often these days, perhaps because enough patients have said 'Nope, never happened to me!' to make doctors reconsider the importance of abuse as a factor.

It is true that some studies have shown that IBS patients report higher levels of sexual abuse than other patients. However, as with other psychological problems, this does not mean that the abuse itself contributed to the IBS, just that the two co-exist. It is no great leap to think that people who suffered abuse as a child may be more prone to gut problems, just as they may be more prone to other physical problems. And there are also studies that show no link between IBS and sexual abuse at all.

  • A re-examination of the relationship between abuse experience and functional bowel disorders Scandinavian Journal of Gastroenterology 2002

    This study examined 53 patients with idiopathic constipation (ie: long-term constipation with no identifiable cause), 50 IBS patients, 51 Crohn's disease patients and 53 healthy control subjects. The researchers asked patients to fill in a questionnaire about their previous abuse experiences, plus further questionnaires focusing on psychological problems, and patients were also interviewed.

    No significant differences were found between the four groups. It was found that patients who reported past abuse demonstrated higher levels of current psychological problems, but this could not be correlated to the type of bowel disorder they suffered from.

    Conclusion: 'These results challenge the current assumption that past abuse experiences may be significant in the later presentation of functional bowel disorders, but suggest that previous abuse experience might be related to a general level of psychopathology.' Pubmed article: Hobbis IC, Turpin G, Read NW

The last word

And the final argument goes like this - if IBS is a psychological problem, why don't psychological treatments work? Maybe it seems like I am spending a lot of time and effort arguing against a psychological basis for IBS, but to be honest I don't really care whether IBS is psychological or physical or caused by little purple men from the planet Zooblon - as long as the theory of what causes IBS can give us a decent corresponding treatment. And the psychological theory just doesn't result in any effective treatment.

Treatments such as psychotherapy have shown to be about as effective as anti-spasmodic drugs or fiber supplements - that is, somewhat effective in some patients, but nowhere near effective enough to be a decent form of treatment for most sufferers. If treatments such as psychotherapy or counseling had shown significant benefits for IBS sufferers then there wouldn't be thousands of sufferers who got told to go home and try not to think about their bowels - they would have been referred for psychological treatment instead, and IBS wouldn't be a leading reason for absenteeism.

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