“A functional symptom is a medical symptom in an individual which is very broadly conceived as arising from a problem in nervous system ‘functioning’ and not due to a structural or pathologically defined disease cause.” – Wikipedia

“… on finding itself unable to discover effective treatments or physiological causes for symptoms, the medical profession [is] subject to a temptation to minimize the explanatory role played by the many gaps in its own current scientific understanding, and instead to grope for theories of psychosomatic etiology …” – Wikipedia


Many have thought IBS is more of a central nervous or mental problem than anything – but this study suggests otherwise

Liked the other disorders allied with irritable bowel syndrome (IBS), the cause of IBS itself has been hard to track down.  The so-called “functional disorders” like fibromyalgia, IBS, and interstitial cystitis are similar in at least six ways:

  • they commonly occur with each other.
  • more women than men are affected.
  • fatigue and pain levels are high.
  • mood disorders are common.
  • similar parts of the brain such as the insula appear to be activated.
  • attempts to find the source of the pain where it occurs (IBS-gut, FM-muscles/joints, IC-pelvic area) have mostly not been successful.

These disorders tend to impair functioning to a great degree, but when researchers turn their instruments on their apparent source of the problem – in this case the gut – they find little or nothing wrong: no structural damage, little evidence of inflammation, nothing. Direct evidence that something has gone wrong in these patients’ muscles, gut, or pelvis has been hard to come by.

The constellation of high rates of fatigue, at least somewhat high rates of mood disorders, and, in particular, few successes at finding problems in the body have led to the perception that these disorders are all in their patients heads.

Foods Provoke Problems – and a Study

Recently, however, studies using newer technology have begun to uncover problems, and this is one of them.  The fact that people with IBS often experience symptoms after eating provided one clue.  Observations that highly fermentable, difficult to digest foods called FODMAPS (fermentable oligo-, di- and mono-saccharides and polyols), in particular, often provoke pain, bloating, etc., provided another clue.


Researchers gave IBS patients food guaranteed to cause problems and then used an MRI to see what happened

Despite failures to find structural abnormalities in the gut, the problems with food intake indicated that something must be happening in the gut. Putting two and two together, radiologist Ragnhild Undseth of Lovisenberg Hospital in Oslo did to her IBS subjects what chronic fatigue syndrome researchers have doing to their ME/CFS subjects for years – she knocked their systems for a loop.

She stressed the guts of IBS patients (and healthy controls) by feeding them an undigestable and highly fermentable substance called lactulose that draws water into the gut. Then she used MRI to assess the water content and diameter of the terminal ileum and descending colon before and after the lactulose moved through it.

Food moves from the stomach to the small intestine where the minerals and nutrients from the food are digested. The terminal ileum is the last way station for digestion at end of the small intestine. Everything that didn’t get digested in the upper part of the small intestine ends up in the terminal ileum. The terminal ileum is also where B-12 gets absorbed.


“The results may suggest a functional impairment of the small intestine in patients with IBS.”

Asking IBS patients to ingest an undigestible substance is akin to asking people with Chronic Fatigue Syndrome to exercise – it’s going to make them worse, and it did. The IBS patients’ gut symptoms soared while the healthy controls experienced few problems.

It also did something bizarre.  The terminal ileum responded in the opposite way in the two groups; it got smaller in the healthy controls and larger in the IBS patients as the lactulose hit their systems, and not just a little larger. The difference between the small bowel diameters in the IBS and healthy controls was a highly significant one.


The IBS groups small intestine acted in opposite ways to food as did the healthy controls

That was really something given that the diameter of the terminal ileum in the IBS patients before the ingestion of lactulose was significantly smaller in the IBS patients than the healthy controls.  To summarize: while the IBS patients TI was smaller than normal before the undigestible food reached it, it got larger when it did. In the healthy controls, the TI was getting smaller, not larger, with the introduction of lactulose.

The degree of water accumulation was not significantly associated with increased symptoms – not an unusual finding in this complex disease.  That could have been due to the small study size and/or the fact that the highly fermentable food substance was doing other things to the gut as well.

Functional Indeed

Why is this important? Because this study indicates that something in this so-called “functional syndrome” has actually functionally gone very wrong–not with the central nervous system, but with the gut.  IBS patients have faced the same bias – that IBS is mental–as have ME/CFS and FM patients.  Studies do show that mind/body therapies can be helpful for some with IBS, but that doesn’t mean that something is not “functionally wrong” either.

In Nordic Science, the lead author of the study, Ragnhild Undseth in Oslo, emphatically stated that her study indicated IBS is not some sort of gut-associated mental disorder.  “No,” she said. “This is not psychological.”

Another researcher added that this study indicates there is an “organic basis” to IBS.


Exactly what is causing the higher accumulations of water is not clear. When food is present the gut should be both absorbing and secreting fluids. Either the small intestine is not emptying as much fluid into the large intestine as expected, or more water is being secreted into the small intestine than normal.

If increased secretion is the problem then mast cell activation may play a key role. An earlier study found increased numbers of mast cells in the terminal ileum, ascending colon, and rectum of diarrhea-prone IBS patients.


A distended small intestine with too much water in it could spell more pain for people with IBS

Low serotonin levels are a possibility as well; serotonin stimulates the gut muscle to move (motility) – an important factor in IBS. Low serotonin levels have been found in gut tissues in IBS, and low serotonin is associated with increased rates of mood disorders. Serotonin, then, fits the bill in several ways – but since serotonin levels vary widely in IBS patients, serotonin is not going to be the answer for all of them.

Indeed, with four types of IBS distinguished so far, no one factor is going to be responsible. While small intestine water accumulation was found in most people with IBS in this study, they weren’t found in everybody; like FM and ME/CFS, IBS is a heterogeneous condition.  (At least four different types of IBS  have been characterized.)



Healthy controls on the left – people with IBS on the right

Why the small intestine’s of the IBS patients reacted in such an unusual fashion is not clear, but what is clear is IBS is a functional disorder – just not in the way the phrase is usually used. When confronted with certain foods the small intestine functions incorrectly; instead of getting smaller – it gets larger. It may be that in order to really get at IBS researchers need to do what they’re doing in ME/CFS – stress the system to more fully reveal its breakdowns. The fact that water secretion or retention in the small intestines is clearly a problem points researchers in a new direction.

The  problems with the terminal ileum make another thing  clear – a FODMAPS-based diet that restricts the intake of ‘highly fermentable’ foods is a very good idea.  It doesn’t  work for everyone with IBS, but it is helpful for many. We’re going to be covering that diet in a future blog that’s coming up – after Thanksgiving :).


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