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What Is The Low FODMAP Diet For IBS?

The FODMAP diet is a therapeutic diet and is often recommended to those who have Irritable Bowel Syndrome (IBS). IBS is a common disorder of the gut-brain interaction, which means that your gut and your brain are not communicating like they should be.⁠ It affects 1 in 7 people, that’s 15% of the population worldwide, and is characterised by symptoms that are not explained by other conditions such as coeliac disease and inflammatory bowel disease.

Unfortunately, many people with IBS are recommended the low FODMAP diet by their doctor but are often not given any information about what it is or any guidance with how to follow it. This can leave them feeling confused and overwhelmed and lead to following the diet incorrectly or completely giving up.

I want to help you feel more confident, so in this blog I am breaking down what exactly FODMAPs are and what the FODMAP diet is.⁠

The acronym for FODMAPs can seem like a mouth full, but I don’t want you to get too caught up with all the technical words.⁠ It really just describes different types of sugars, or carbohydrates, that are found in a lot of everyday foods.⁠ It stands for:

  • Fermentable

  • Oligosaccharides

  • Disaccharides

  • Monosaccharides

  • And Polyols

These are poorly broken in your small intestine and are then fermented by the gut bacteria in your large intestine. This produces gas which leads to the symptoms associated with IBS including:

  • Uncomfortable bloating and stomach distension (pregnant looking belly)⁠

  • Excessive and/or painful wind⁠

  • Stomach pain and discomfort⁠

  • Constipation and/or diarrhoea⁠

FODMAPs are also small in size and increase the amount of water delivered throughout your gut. This is called an osmotic effect. The gas produced by the large intestine in combination with this osmotic effect can cause changes to your guts motility or the way it moves resulting in constipation and/or diarrhoea.

FODMAPs are found in many common foods including fruit, vegetables, grains and dairy and there are 5 main FODMAP groups:⁠

  • Fructose⁠

  • Lactose⁠

  • Galactans or Galacto-oligosaccharides (GOS)⁠

  • Fructans or Fructo-oligosaccharides (FOS)⁠

  • Polyols, which include sorbitol and mannitol⁠

Although these carbohydrates are poorly absorbed in everyone, they are believed to affect and cause symptoms in people with IBS because their guts are more sensitive. It’s important to remember that FODMAPs are not the cause of IBS, but limiting these in your diet can help you control your IBS symptoms.

The FODMAP diet is a therapeutic diet used as part of the medical treatment and management for those with IBS. Research shows, that those who follow the FODMAP diet with the support of a specialised IBS Dietitian (like me), get better relief from their symptoms and it can help improve gut symptoms in up to 80% of people with IBS. That’s pretty amazing, right?!

However, one of the most common mistakes I see people make is following the low FODMAP diet for too long without moving onto the reintroduction phase. It is important to note that the FODMAP diet has 3 phases and that the entire FODMAP process should be completed to avoid restricting your diet unnecessarily.

The 3 phases of the FODMAP diet are:⁠

Phase 1 – Low FODMAP or Elimination

This phase of the diet requires you to limit any high FODMAP foods and substitute these with low FODMAP alternatives to help relieve uncomfortable gut symptoms. Reducing high FODMAP foods enables you to determine if you are responding to the low FODMAP diet and whether it is resulting in a decrease in your IBS symptoms.

The low FODMAP phase can be restrictive, and people often struggle with the amount of variety in their diet and adding flavour to their meals. FODMAPs also contain fibre and are natural prebiotics, so those on a low FODMAP diet can struggle with meeting their fibre requirements which can lead to constipation. So, a big consideration is the long-term consequences of a low FODMAP diet. And this is one of the reasons why it is only recommended for the short period of 2-6 weeks.

Phase 2 – Reintroduction or Challenge

This can take anywhere from 6-12 weeks. This phase involves the challenging or reintroduction of each of the FODMAP groups in a systematic way that is well planned to ensure that the results you get are clear and accurate. During this phase you will continue to follow the low FODMAP diet as your baseline diet, with each FODMAP group being challenged one at a time. A specialised IBS Dietitian will give tailored advice and guidance on which food to use for challenging, the order to reintroduce them and the amount you should use.

This phase helps to determine if FODMAPs may be triggering your symptoms. It not only helps to identify which FODMAP groups you may be sensitive to, but also how much you are able to tolerate. This is a particularly important part of the diet as it will identify whether you may be able to have a particular FODMAP or tolerate a small, moderate or large amount of a FODMAP before getting symptoms.

Phase 3 – FODMAP Personalisation

This phase is ongoing and is unique to everyone. It is where you develop your long-term personalised IBS diet. During this phase you will reintroduce the different FODMAP groups back into your diet based on your individual tolerance levels that you discovered during your FODMAP challenges in phase 2.⁠ This phase is a particularly important phase of the FODMAP diet as it enables us to develop a long-term balanced diet to ensure you are able to optimise your overall gut health and improve your overall health and quality of life.

A key consideration and an important thing to note is that the FODMAP diet should be undertaken with the guidance of an Accredited Practising Dietitian or Registered Dietitian that is experienced in IBS, as it is a complex and restrictive diet that can potentially lead to nutrient deficiencies if not properly followed. As an expert IBS and FODMAP Dietitian I can provide you with appropriate low FODMAP substitutes to your favourite foods while ensuring you are getting all the nutrition you need with a healthy, balanced diet and a wide variety of foods. Additionally, it is not intended to be a long-term solution for managing IBS symptoms, but rather a tool to help identify trigger foods and guide the development of a personalised dietary plan.


If you’re FINALLY ready to ditch the diet confusion and find relief from your IBS, CLICK HERE to watch my FREE Masterclass to discover my proven 3 phase roadmap and the surprisingly simple steps you can take to start reclaiming your life from IBS in as little as 2 weeks.



  1. Gandy J & the British Dietetic Association. Manual of Dietetic Practice–Fifth Edition. 2014: 460-466.

  2. Gibson PR, Shepherd SJ (2010). Evidence-based dietary management of functional gastrointestinal symptoms: The FODMAP approach. Journal of Gastroenterology and Hepatology. 25: 252–258.

  3. Longstreth GF, Thompson WG, Chey WD, Houghton LA, Mearin F, Spiller RC (2006). Functional bowel disorders. Gastroenterology. 130: 1480–1491.

  4. National Institute for Health and Care Excellence (NICE) (2008). Irritable bowel syndrome in adults: Diagnosis and management of irritable bowel syndrome in primary care. CG61.

  5. Tuck C & Barrett, J (2017). Re-challenging FODMAPs: the low FODMAP diet phase two. Journal of Gastroenterology and Hepatology. 32 (Suppl 1): 11–15.


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