25 February 2019

When a low FODMAP diet doesn’t work. Part 2 of 2

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By Dr. Jane Varney - Research Dietitian

If you haven't read last weeks installment - When a low FODMAP diet doesn't work, Part 1 - click here to read it first.



If you achieved an inadequate response to a low FODMAP diet, you may need to consider whether the treatment was sufficiently targeted to the underlying cause your IBS symptoms. A number of pathophysiological abnormalities account for IBS symptoms. These include:

  • Visceral hypersensitivity  - this is when nerves that line the intestine are over-active and can result in normal changes in the gut  (such as increases in gas and water) being experienced as painful episodes of pain and bloating. Visceral hypersensitivity  is thought to be present in around 65% of cases of IBS and may be indicated by the presence of abdominal pain
  • Altered gastrointestinal motility – this refers to abnormally fast, slow or uncoordinated movement of the intestines and the contents within. If fast colonic transit is present it may be indicated by the presence of diarrhoea, while slow or uncoordinated colonic transit may manifest as constipation
  • Enhanced gut-brain communication – This refers to alterations in the two-way communication that occurs between the brain and the gut. Patients whose symptoms are triggered by stress and anxiety may have enhanced gut-brain communication 
  • Alterations in the gut microbiota – Some research has shown differences between the microbiota of people with and without IBS. These differences may account for cases of post-infectious IBS
  • Other possible causes -  e.g. increased mucosal permeability, immune system activation and low-grade inflammation, but less is known about their precise role in triggering IBS symptoms. 


One important point here is that these physiological abnormalities (or causes of IBS) are probably not all present in all patients. For instance, some patients’ symptoms may be primarily due to the presence of visceral hypersensitivity, while others may experience symptoms due to problems with motility. 


But why do we care about what causes IBS symptoms? The reason is that different therapies target different physiological processes. For instance, certain drugs may target gastrointestinal motility by speeding up or slowing down transit through the gut; psychological therapies may help to reduce stress and anxiety which may otherwise trigger symptoms, and probiotics may alter the gut microbiota. When it comes to the low FODMAP diet, this therapy is thought to primarily target visceral hypersensitivity. That is, reducing FODMAP intake reduces gas and water movement into the intestine, which in turn reduces stretching of the intestinal wall, and this limits the exaggerated sensations of pain and bloating which characterises IBS in some people. 


So if you have responded poorly to a low FODMAP diet, it may be worth chatting to your doctor or dietitian about other therapies which may more specifically target the underlying cause of your IBS symptoms. Other therapies to consider include:


But remember, it is best to try one therapy at a time, so you can see what is working. 


Need more help? Seek the assistance of a Monash FODMAP Trained Dietitian. 


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