The low FODMAP diet and irritable bowel syndrome (IBS)

Evidence shows that THE LOW FODMAP diet can significantly improve symptoms in more than 3 out of 4 (75%) people suffering from Irritable Bowel Syndrome (IBS).

The LOW FODMAP diet can help those suffering from the following digestive symptoms:

  • Bloating

  • Abdominal pain/discomfort

  • Flatulence

  • Altered bowel habits - diarrhoea and/or constipation

And it may help those with IBS related systemic symptoms, including:

  • Reflux

  • Low energy

  • Low mood

  • Anxiety

  • Poor sleep

First... seek medical advise

It is important that you talk to your Doctor or Dietitian about your digestive symptoms before commencing THE LOW FODMAP DIET. This is to ensure that you have relevant tests and/or examinations performed before self-diagnosing and self-treating. Relevant examinations may include stool tests, blood tests, an abdominal ultrasound, breath tests, or scopes.

More than just gut issues...

Although it feels that most of your symptoms are concentrated in your gut (e.g. bloating, cramping, discomfort, bowel issues), it is very common to also suffer from mental strains, such as anxiety, a lowered mood, brain fog and/or social discomfort.

The gut-mind connection

Your gastrointestinal (G.I) system contains millions of nerves that branch from your gut, all the way up to your brain. Further to this, your gut produces neurotransmitters that send signals along that gut-brain highway, as well as containing buckets of bacteria that do all sorts of things that impact on your brain.

We call all this “The Gut-Mind Connection”.

And remarkably, it has been linked to alterations in mood, anxiety, depression, memory, food cravings, eating behaviours and ultimately life choices.

An IBS diagnosis

IBS (aka Irritable Bowel Syndrome) is a condition that will be diagnosed after excluding certain diseases (e.g. IBD and Coeliac Disease), as well as when a certain number of digestive symptoms fit into a particular IBS criteria; formally known as the Rome IV Diagnostic criteria.

Rome IV Criteria for diagnosis of IBS

If you suffer from recurrent abdominal pain, on average, at least one day per week over the last three months, as well have two or more of the below symptoms that are associated with your abdominal pain, then an IBS diagnosis may be made.

Associated symptoms:

  • Abdominal pain related to defecation (pooing)

  • Associated with a change in the frequency of pooing

  • E.g. Going more than 3 times per day, or less than 3 times per week

  • Associated with a change in the form (appearance) of your poo

  • E.g. Diarrhoea or constipation or alternating diarrhoea and constipation

Types of IBS

  1. IBS-C = Constipation predominant

  2. IBS-D = Diarrhoea predominant

  3. IBS-M = Mixed bowel habits

The cause of IBS

The cause of IBS is still unknown, however it is believed that the entire gut-brain axis is affected. It is also known that there is a higher risk for IBS post infection (e.g. gastro) and after antibiotic use.

Psychological factors such as anxiety and depression likely play a role in the severity of IBS symptoms, as well as its persistence. This may be evident during stressful times (e.g. work/job/exam pressure).

IBS is a functional GI disorder

IBS is categorised as a functional GI (gastrointestinal) disorder, which is a disorder of gut-brain interaction. Functional GI disorders are classified by GI symptoms related to any combination of the following:

  • Motility disturbance – issues with the movement of food and waste through the GI tract.

  • Visceral hypersensitivity – heightened experience of pain in the organs, particularly in the gut.

  • Altered mucosal function – the gut wall (mucosa) is altered.

  • Altered immune function – the guts immune system is altered.

  • Altered gut microbiota – the amount and/or types of gut bacteria may be compromised.

  • Altered CNS function – changes in how the brain communicates back and forth with the gut.

A LOW FODMAP diet can help those with IBS... but what are FODMAPs?

FODMAPs are certain types of carbohydrates that are found in a variety of foods. They are poorly absorbed in the small intestine and reach the large intestine where they are fermented by gut bacteria. This results in gas production. Furthermore, they have an osmotic effect, meaning they suck water into the bowel.

The word FODMAP is an acronym

  • Fermentable – fermented by healthy bacteria that live in the large intestine

  • Oligiosaccharides

  • Fructans – e.g. wheat, onion, garlic, ripe bananas, zucchini

  • GOS – e.g. legumes, pistachios, cashews, green peas, whole soy bean milk

  • Dissacharides

  • Lactose

  • Monosaccharides

  • Fructose – e.g. honey, mango, apples, pears

  • And

  • Polyols

  • Sorbitol – e.g. apples, pears, artificial sweeteners

  • Mannitol – e.g. cauliflower, mushrooms, watermelon

How do FODMAPs affect people with IBS?


= FODMAPs are small in size, which influences their effect to draw fluid into the gut (osmosis). This can result in an increased amount of fluid in the intestinal tract.


= FODMAPs are poorly absorbed in the small intestine, causing them to end up in the large intestine. Here they are fermented by gut bacteria, resulting in gas production. This can lead to: wind, bloating, abdominal pain, and abdominal discomfort.


= this can alter gut motility, which may contribute to: diarrhoea and/or constipation

A word of advise...

There are lots of low FODMAP lists that you can find on the internet, however these are often inaccurate, and may set you up for failure. For best results, work with a Dietitian that specialises in IBS and the low FODMAP diet.