The low FODMAP diet : guide to getting started

What is the low FODMAP diet? (1)

The low FODMAP diet is a three phase diet which aims to improve symptom control and identify triggers in individuals with irritable bowel syndrome (IBS). It is a complex and restrictive diet which should only be followed by individuals with a definite diagnosis of IBS and with the guidance of a dietitian trained on the use of the low FODMAP diet. If any of you would like to seek the help of a private dietitian check out the Kings college register and Monash university register to ensure you work with a FODMAP trained dietitian.

The three phases include:

  1. Elimination (2-6 weeks). A low FODMAP diet is implemented to achieve symptom improvement.
  2. Reintroduction (6-8 weeks). Moderate and high FODMAP foods are reintroduced to test individual sensitivities.
  3. Personalisation. Expand the diet and establish a ‘personalised’ FODMAP diet based on the identified sensitivities in phase 2.

In this post we shall focus on the elimination phase. Reintroduction and personalisation will be covered in future posts.

What does FODMAP stand for? (1, 2)

It stands for Fermentable Oligosaccharides, Disaccharides, Monosaccharides and Polyols.

These are short-chain carbohydrates (sugars) which are either poorly absorbed or not absorbed at all in the gut and are rapidly fermented by bacteria in the large intestine.

How do FODMAPs cause IBS symptoms? (1, 2)

  • they attract water into the small intestine causing distension
  • fermented by bacteria in the large bowel leading to gas production, bloating and wind
  • stretching of the intestines due to an increase in water and gas can lead to abdominal pain due to overactive nerves (hypersensitive gut) in individuals with IBS.

Let’s have a look at the individual FODMAP subgroups, how each of these act in the gut and how they may trigger symptoms.


These include fructans and galactooligosaccharides (GOS). Both fructans and GOS are short chains of 2-10 fructose sugar units. Humans lack the enzyme needed to digest them therefore, these sugars end up in the large intestine where they are fermented causing gas production and wind. This occurs in everyone, however due to increased gut sensitivity in individuals with IBS this leads to bloating, abdominal discomfort/pain.

Examples of foods high in fructans includes onion, garlic, wheat, rye

Examples of foods high in GOS includes beans and pulses

Disaccharide: Lactose

Lactose is made up of one glucose and one galactose sugar unit. Lactose is a sugar found in dairy products such as milk, yoghurt and soft cheese. This is poorly digested and absorbed in people who lack an enzyme called lactase. Undigested lactose attracts water into the large intestine and undergoes fermentation by gut bacteria leading to distension, bloating, flatulence, abdominal pain and diarrhoea. The severity of the symptoms will depend on the amount of lactose consumed.

Monosaccharide: Fructose

Fructose is a simple sugar, made up of one sugar unit. It is absorbed slowly and its presence in the small intestine attracts water causing abdominal distension. When excess fructose reaches the large intestine it is fermented and causes gas production and bloating. Water moving into the large intestine can also lead to diarrhoea.

Examples of foods high in fructose include honey, mango, figs

Polyols: Sorbitol and Mannitol.

These are sugar alcohols. They occur naturally in some fruit such as apples and vegetables such as mushrooms but they are also added to processed foods as sugar substitutes and humectants. They can often be found in sugar free products such as chewing gum. Polyols like fructose are absorbed slowly and excess polyols attract water into the small intestine leading to distension. Any unabsorbed polyols are fermented by bacteria in the large intestine leading to gas production causing bloating and flatulence. Water moving into the large intestine can also lead to diarrhoea.

Watch the video below made by Monash university explaining this process visually.

Starting the elimination phase of low FODMAP diet

This phase involves removing all moderate and high FODMAP foods from your diet for 2-6 weeks or until adequate symptom relief is achieved.

Step 1: Download the Monash university FODMAP app. This does involve a one time payment however it is truly invaluable. The a team of scientist at Monash university created the low FODMAP diet and test all the foods for FODMAP content and the app is updated regularly with new foods.

Step 2: Start to familiarise yourself with the app and FODMAP content of foods.

Step 3: Write down what you usually eat on a day to day basis and look for these products/ ingredients in the app. Identify which foods in your diet are high in FODMAPs and find suitable alternatives which are low FODMAP. Example if you usually snack on an apple, swap this for a low FODMAP fruit example orange, strawberries or kiwi. A dietitian can help you identify high FODMAP foods in your diet and discuss changes whilst ensuring nutritional adequacy.

Step 4: Do the same process with any of your favourite recipes. Whilst removing certain foods can be challenging, you can still make great tasting food without. See the pictorials below showing low FODMAP alternatives for onion and garlic.

Step 5: Use the information gathered from steps 3 and 4 and start putting together a shopping list. If you want some more inspiration on low FODMAP products available in UK supermarkets have a look at this post.

Step 6: Learn how to read food labels to identify high FODMAP ingredients by reading this post.

Step 7: Check the safe portion sizes for low FODMAP foods. Each recommended green serving is per meal. A gap of 4-5 hours between each serving is recommended. This means if you have a low FODMAP serving at lunchtime, you can have this again for dinner.

Step 8: Ensuring nutritional adequacy during the elimination phase

Due to its restrictive nature the low FODMAP diet can compromise nutrient intake. It is important to maintain a varied diet to minimise the risk of developing any nutrient deficiencies. Studies have shown individuals following a low FODMAP diet were at risk of inadequate intakes of calcium, iron, and fibre (3).

Have a look at the brief guide below on ensuring a balanced diet during the elimination phase focusing on nutrients at risk. Examples of low FODMAP sources are provided (4).

  • Protein: Aim for 2-3 portions of protein a day. This is also important to ensure adequate iron intake. Examples of protein include poultry such as chicken, beef, fish, and eggs. Vegan sources include firm tofu, tempeh and small quantities of canned beans and lentils.
  • Carbohydrates: Include a carbohydrate source at mealtimes. Example: rice, potato, gluten free bread, gluten free pasta, porridge, sourdough bread
  • Vegetables: Include vegetables with meals. Aim for at least a third of your plate. low FODMAPs examples include salad, carrots, red bell pepper
  • Fruit: Include 2 palm sized portions of fruit low FODMAP examples include orange, strawberries, grapes
  • Fat: Include healthy sources of fat in the diet such as rapeseed, olive oil, nuts and seeds, olives. If you are watching you weight limit oil in cooking to 1 teaspoon per person.
  • Calcium: Include 2-3 portions of calcium containing products a day. Example lactose free yoghurt and milk, hard cheeses or dairy free products such as almond/rice milk fortified with calcium and calcium set tofu.
  • Iron: Include iron sources in your diet. Deficiency can lead to anaemia. Low FODMAP sources include red meat, liver, eggs, tofu, peanuts, sunflower seeds, sesame seeds, kale, spinach, beans* and lentils*. *watch portion size
  • Vitamin B12: If you are vegan ensure you are including sources of B12 in your diet. Inadequate intakes can lead to anaemia. Aim to include 3 servings of foods fortified with B12 aiming for 3 micrograms a day. Examples of low FODMAP fortified products include almond milk, rice milk, gluten free cornflakes. If you are not able to include these in your diet daily take a B12 supplement daily providing 10 micrograms.
  • Folic acid: Inadequate intakes can lead to anaemia. Good sources include dark green leafy vegetables such as spinach & kale; oranges, wholegrains, poultry, pork and shellfish.
  • Iodine: The main source of iodine in the UK is milk and dairy products. Dairy free alternatives are not fortified with iodine. Good low FODMAP iodine sources include lactose free milk and yoghurt, cheese, seaweed and white fish such as cod & haddock. You can also purchase iodised salt.
  • Fibre: Ensure you get enough fibre by including low FODMAP fruit and vegetables, opting for wholegrains e.g. porridge, brown rice & seeded gluten free bread, snacking on low FODMAP seeds/ nuts, adding ground flaxseeds/ linseeds or chia seeds to cereal, salads. Increase your fibre intake gradually, particularly if your diet is usually low in fibre to avoid gastrointestinal symptoms such as bloating and gas.
  • Vitamin D: Vitamin D is produced when our skin is exposed to the sun. Some foods such as oily fish, egg yolk, fortified cereal & margarine contain vitamin D however this alone tends to be insufficient to meet requirements. It is recommended to take a 10mcg supplement in autumn and winter. (5)

Busting myths

  1. The low FODMAP diet is a gluten free diet

    Gluten is a protein and does not need to be avoided unless you have been diagnosed with coeliac disease. Products containing wheat, rye and barley are often avoided on a low FODMAP diet due to the presence of fermentable carbohydrates. However, not all these products need to be avoided. Example sourdough bread can still be enjoyed on a low FODMAP diet.

    Whilst gluten free products are often low FODMAP they are not always. If purchasing a gluten free product be sure to check the ingredient list for any high FODMAP ingredients.
  2. You can enjoy cheese on the low FODMAP diet
    The low FODMAP diet is not a dairy free diet but lactose free or low lactose diet. Products such as hard cheeses example cheddar and parmesan cheese are virtually lactose free due to the processing and fermentation undertaken. Most other cheeses also have a substantial low FODMAP serving size.
    Most individuals with lactose intolerance can still tolerate some lactose in the diet therefore even small amounts of cow’s milk, yoghurt and cream may be tolerated. However if consuming these in larger quantities you can opt for lactose free alternatives.

    As mentioned previously I recommend referring to the Monash University FODMAP app for more information on products as low FODMAP servings.
  3. The low FODMAP diet is a forever diet.
    The elimination phase of the low FODMAP diet is designed to help improve your symptoms and allow you to later reintroduce foods and identify your own personal triggers. The goal is to achieve a varied and diverse diet whilst still maintaining satisfactory symptom control.

How long should I follow the elimination stage before moving to reintroduction?

You should do the elimination stage for 2-6 weeks. Once you achieve a significant improvement in symptoms you can move on to phase 2: reintroduction.

This is a complex diet and it can take a while to take it all in and get it right. The odd slip up is expected whilst still getting to grips with the intricacies of this diet. Take time to prepare, get organised, and plan your meals and snacks. Preparation is key.

Best of luck on your low FODMAP journey.


  1. Monash University FODMAP for IBS Dietitian course, 2019. Module  5 Phase 1 low FODMAP diet and practical skills. [Accessed 12/9/2020].
  2. Monash University FODMAP diet app version 3.0.4, 2020. Chapter 3 What are FODMAPs. [Accessed 12.9.2020]
  3. Staudacher et al., 2015. Advice from a dietitian regarding the low fodmap diet broadly maintains nutrient intake and does not alter fibre intake. Gut, 64 (1): A143-A144.
  4. Monash University FODMAP diet app version 3.0.4, 2020. Food Guide. [Accessed 12.9.2020]
  5. Public health England, 2016. SACN Vitamin D and health report. UK: PHE

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