What is a low FODMAP diet and can it help with IBS?

Around one in five people in the UK will experience IBS during their life and around two thirds of the people affected are women. This often distressing condition affects individuals in different ways, symptoms can vary between constipation, diarrhoea or a mixture of both.


IBS is diagnosed if you have been experiencing the presence of abdominal discomfort or pain when going to the toilet (defecation) and/or accompanied by a change in bowel habit. Naturally, it goes without saying that these symptoms are distressing, and often make social situations uncomfortable.

This can often affect a person’s self-confidence in relation to what they eat, or even what to wear as the onset of bloating can drastically change after a meal.

To help alleviate these symptoms, a registered nutritionist or dietitian can work to identify foods to help alleviate the symptoms. This can range from supplementing the diet with probiotics, increasing unfermentable fibre in the diet or following a low FODMAP diet.

What is the low FODMAP diet?

These are types of sugars that the body is not able to digest very well and can be present in a range of foods. FODMAP stands for:

  • Fermentable: food that can be fermented in the gut.
  • Oligosaccharides: carbohydrates formed when three to 10 simple sugars are linked together.
  • Disaccharides: sugar formed when two monosaccharides are joined e.g. sucrose or lactose.
  • Monosaccharides: sugar that cannot be broken down into a simpler sugar such e.g. fructose.
  • Polys: sugar-free sweeteners such as erythritol, maltitol, mannitol, sorbitol and xylitol.

What are the high FODMAP foods?

Common high FODMAP foods include onions, wheat, garlic, lactose, sweeteners, beans and pulses, cauliflower, avocados and apples.

How do high FODMAP foods cause IBS symptoms?

In some individuals with IBS, it is thought that they poorly absorb or digest certain sugars that pass through the small intestine and enter the colon. These sugars are then fermented by bacteria, releasing excess gas causing bloating, wind and abdominal pain.

Fructose, lactose, and polyols tend to retain water in the bowel and may result in loose motions and diarrhoea.

How do I start a low FODMAP diet?

The low FODMAP diet follows three steps.

Step 1. Introducing the low FODMAP diet

This is to be commenced under the supervision of a registered nutritionist (RNutr) for a period of two to six weeks. During this phase, you only eat foods that are low in FODMAPs. This is a substitution diet, whereby you swap one food for another e.g. switch your daily apple for an orange.

Step 2. Reintroduction of high FODMAP food groups

This step involves reintroducing foods back into your diet in a structured way to determine which foods and FODMAPs trigger symptoms. Your nutrition professional will advise which FODMAPs to reintroduce first and each one will be monitored, and the data collected. 

Step 3: Your personal diet

The third step of the diet involves establishing a longer-term diet that is personal to you and your trigger foods. Once your nutrition professional has interpreted your food triggers and tolerances, you can begin to reintroduce foods and FODMAPs that were tolerated well and avoid the foods that triggered your symptoms.

Remember, if you'd like to make any changes to your diet or are keen to start a low FODMAP diet, please do so under the supervision of a nutritional professional. 

The views expressed in this article are those of the author. All articles published on Nutritionist Resource are reviewed by our editorial team.

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