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FODMAPs & the Low FODMAP Diet

5 June, 2020

FODMAPs and the Low FODMAP Diet

Approximate reading time: 4-5 minutes

FODMAPS & Irritable Bowel Syndrome

FODMAP is an acronym which stands for Fermentable Oligo- Di- Mono-saccharides And Polyols.

FODMAPs are a group of short chain carbohydrates (or sugars) that are:

  • Small in size
  • Poorly absorbed or not absorbed at all in the small and large intestine
  • Fermented by gut bacteria

Sugars classified as FODMAPs include oligosaccharides (fructans and GOS), polyols (sorbitol and mannitol), fructose and lactose.

How they work

The nerves in the intestines are overactive in Irritable Bowel Syndrome (IBS). Experiencing increasing gas and water in the gut is very normal when digesting food, but individuals with IBS can experience this as episodes of excessive bloating, diarrhoea and/or constipation, abdominal pain and excess gas.

When we consume FODMAP rich foods, they pull water into the small intestines. This stretches and expands the guts causing changes to the natural digestive movements to push food through the digestive tract.

FODMAPs are poorly absorbed in the small intestine. In the large intestine, FODMAP foods provide energy for the bacteria. The bacteria ferments the FODMAP sugars which causes excess gas production.

All of these actions add up to excess gas in the intestine, stretching the walls of the intestines. Because of these nerves being highly sensitive, people with IBS will experience more frequent and painful sensations and discomfort when this occurs.

What is the Low FODMAP Diet?

The Low FODMAP Diet consists of three phases.

Phase 1

Phase 1 is where an individual follows a diet overall low in all FODMAP subgroups, or personalised depending on their individual needs. This aims to achieve symptom relief. High and moderate serves of FODMAPs are substituted with low FODMAP alternatives.

This usually takes around 4-6 weeks, aiming to have significant symptom relief by the end of this phase.

Consulting an Accredited Practising Dietitian is important when beginning a Low FODMAP Diet, as they can investigate triggers and potential issues throughout this phase and beyond.

Phase 2

This is where FODMAPs are slowly reintroduced into the diet. This is a “challenge” phase, where different FODMAP groups are tested for tolerance or a symptom response.

For example, an individual may only be intolerant to lactose, so testing foods high in other sugars like fructose or polyols will be well tolerated. They may trial apples, peaches and cauliflower and find they have no symptoms at all. This is when we can “tick” off these types of foods as tolerated. However, this person may trial milk, cream or other dairy products and find they have symptoms.

We then look for a tolerance point for these foods. For some, it may be ½ glass of milk, others it may be more or less. It is important that Phase 2 is taken gradually, to avoid the stacking of FODMAPs each day, and so any reactions or symptoms can be pinpointed to a specific type of FODMAP subgroup.

Phase 3

This last phase is the personalised part of the FODMAP Diet.

This is when an individual has gone through the first two phases with their dietitian, found symptom relief and figured out what portions of what foods they can tolerate. A person may know they do not respond well to lactose, so buy lactose-free milk or choose dairy alternatives such as calcium-fortified soy or almond milk.

This is the long-term phase, which we aim to maintain after the Low FODMAP Diet has been completed. As IBS symptoms and responses can change over time, ongoing trialling and FODMAP challenges can be conducted over a longer time period.

All of these phases are conducted with the support and evidence-based guidance of an Accredited Practising Dietitian, to ensure nutritional adequacy is maintained and consistent throughout these phases. This is also to ensure that other medical issues can be ruled out.


Approximately 75% of individuals diagnosed with IBS will find relief and success from a low FODMAP diet, however, some may not experience this.

  • Most people find their symptoms do not resolve completely
  • Responses to a Low FODMAP Diet can be highly individual
  • Wind or bloating is very normal! It is important to accept these as normal bowel habits, but to note the severity of these symptoms as acceptable and unacceptable depending on any diet changes
  • Symptoms can fluctuate and change over time depending on stress, anxiety, physical activity, sleep, hydration, mood and how our diet changes with the seasons

If your gastrointestinal symptoms have been difficult to cope with, booking an appointment with an Accredited Practising Dietitian can be a way to investigate symptom relief from potential triggers in your diet. Seeing a doctor is also very important to rule out other clinical issues such as Coeliac Disease, IBD, or other additional medical diagnoses that have some overlapping symptoms with IBS.

Following the Low FODMAP Diet is a short-term way of finding long-term symptom relief, and should be done with the support and guidance from an expert. The diet may seem difficult at first, but with easy recipes ideas, resources and one-on-one consultations, having the support of a dietitian throughout your nutrition journey is invaluable.

Appointments available in Moonee Ponds or online.


  • FODMAPs are small sugars that difficult for the gut to absorb.
  • With IBS, the nerves are sensitive and the intestinal walls are stretched with FODMAP foods.
  • A Low FODMAP Diet is a short term diet that decreases bloating, constipation / diarrhea and abdominal pain in 75% of IBS sufferers.
  • An Accredited Practicing Dietitian, especially one with specialised training in FODMAPs, should be consulted for tailored advice on this complex diet.

About the Author

Alex Sherman - Accredited Practicing Dietitian & Accredited Nutritionist

Alex is an Accredited Practicing Dietitian and Nutritionist. She's crazy passionate about nutrition - even to have studied for over 6 years at university, including post-graduate studies in FODMAP Diet for irritable bowel syndrome (IBS). She offers clear and practical advice tailored to your health goals.