What is IBS and how to manage it?

  • IBS (Irritable bowel syndrome) is a chronic condition defined by abdominal pain or discomfort, with changes in stool frequency and consistency.

  • It affects more than one in five Australians and is twice as common in women.

  • Key symptoms include recurring episodes of diarrhoea or constipation, abdominal discomfort and bloating.

Causes of IBS

  • Despite IBS being such a common condition, its cause is still unknown.

Visceral hypersensitivity (VH) plays a major role in its pathogenesis. As the name suggests, VH means you have a heightened sensitivity to pain in your viscera (internal organs).
  • So those with IBS have a lower pain threshold in their gut, meaning even minor intestinal distension, caused by gas producing foods (e.g. FODMAPs), will cause significant discomfort.

  • Research shows that nearly 50% of IBS sufferers experience anxiety, with up to 15% also experiencing depression.

  • Stress plays a major role in IBS likely through the secretion of pro-inflammatory cytokines and cortisol, which in turn affect GI motility, permeability and VH.

  • Ultimately, IBS is defined as an alteration in your gut brain axis.

The link between diet and IBS

  • What you choose to eat, or not eat, modulates your gut microbiota composition, diversity and vitality. Your choices also influence your colonic fermentation, GI motility, visceral sensation, your GBA and your immune regulation.

  • On top of this, you might also have food allergies or intolerances that can cause or exacerbate your GI symptoms.

  • Note that food allergies involve your immune system, whereas food intolerances are non-immune mediated.

Food intolerances

  • More than 90% of IBS sufferers report that food triggers their GI symptoms and in turn limits foods they relate to their symptoms.

  • Knowing your specific food intolerances, including thresholds, is key to navigating your IBS and overall nutritional intake.

  • FODMAPs are often a key culprit.

More than 3 in 4 people with IBS experience symptom improvement after following a low-FODMAP diet.








FODMAPs are short-chain carbohydrates that exert a high osmotic effect and are rapidly fermented in your gut.

They are found in a wide variety of foods and are tolerated well by most, however often not so well by those with IBS.


FODMAPs are poorly absorbed in the small intestine (of all people) because of slow transport mechanisms, reduced digestive enzymes, lack of specific hydrolases, or simply because they are too big. In turn, they end up in the large intestine where they are rapidly fermented by gut bacteria.

Diarrhoea: Due to their high osmotic effect, certain FODMAPs cause extra water to be sucked into the intestinal tract. This can result in loose watery stools (diarrhoea).


Constipation: In contrast, some IBS sufferers may suffer constipation because of higher numbers of methanogenic bacteria living in their bowel. These specific bacteria produce methane gas upon fermenting FODMAPs, a gas that has been shown to slow GI transit, leading to less frequent and harder stools (constipation).