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What To Do When The FODMAP Diet Hasn’t Relieved Your IBS

Did you know that you there are other types of food that can cause symptoms in people with IBS besides FODMAPS? These are called food chemical intolerance, but before we get stuck into what these are I think it is important to understand the difference between a food allergy and a food intolerance, as these are not the same.

A food allergy is due to our immune system reacting to a food protein that the body wrongly thinks is harmful, which causes a person to have a reaction and get symptoms. Whereas a food intolerance does not involve the immune system and reactions are rarely life-threatening. A food intolerance is when a person cannot properly digest or fully break down and absorb certain foods.

What are Food Chemicals?

Food chemicals are found naturally in many everyday foods and food additives and there is a significant amount of variation in the make-up of natural chemicals in food. For most people these do not cause any issues or symptoms. However, in people who are more sensitive, such as those with Irritable Bowel Syndrome (IBS), they can cause symptoms.

The most common natural chemicals found in foods are salicylates, amines, and glutamate. These are most likely to cause symptoms is sensitive people as they are found in a large number of many different common foods and are therefore eaten the most in people’s diets.


These are natural chemicals found in plants and are present in many fruits, vegetables, nuts, tea and coffee, honey, herbs and spices, flavourings, and most alcohols. The level of salicylates in food decreases as the food ripens and levels are highest in the skin. Salicylates are also found in some medications, such as aspirin and herbal remedies.

They are also found in many natural flavourings used in food, drinks and medications, such as mint and fruit flavours and are used to scent perfumes, washing powders, cleaning products, toiletries and botanical oils, particularly lavender, eucalyptus and tea tree.


These are a product of either protein breakdown or fermentation. They are found in meats, cheese, fish products, fruits, vegetables, and many alcoholic beverages. The level of amines found in fruit increases with ripening, such as in banana, tomatoes and avocado. Foods particularly high in amines include chocolate, jams and flavoured spreads, fruit juices, sauces and fermented products such as beer, wines and yeast extracts.


Glutamate is an amino acid present in most foods as it is a building block for proteins. Glutamate in used in the preparation of many meals as it enhances the flavours of foods. Foods containing natural glutamate include cheese, tomato, mushrooms, meat and yeast extracts, soy sauce and stock cubes. Monosodium glutamate (MSG) is also often used as an additive in soups, sauces and snack foods to increase the flavour and is commonly used in Asian cooking.


FUN FACT: Did you know that “organic” foods may actually not be better for those with a food intolerance? 

Why you might ask…growing foods without pesticides and herbicides actually results in them significantly increasing the amount of salicylates and other chemicals that they naturally produce.

However, you can minimise and avoid the amount of pesticide residues and natural chemicals by peeling the skin off your fruit & vegetables and removing the outside leaves of lettuce & cabbage.


Food Chemical Intolerance

Food chemical sensitivity or intolerance occurs when these chemicals (salicylates, amines, glutamate and food additives) result in someone experiencing symptoms. When ingested these chemicals cause reactions by irritating nerve endings in different parts of the body which leads to symptoms. These symptoms can be different in each person and can include;

  • Bloating

  • Nausea

  • Stomach discomfort or pain

  • Diarrhoea

  • Headaches and migraines

  • Recurrent hives and swelling

  • Sinus trouble

  • Fatigue or feeling run down

  • Flu-like aches and pains

In children symptoms can include;

  • Irritability and restlessness

  • Exacerbation of behavioural problems such as ADHD.

In baby’s symptoms can include;

  • Colic

  • Irritability

  • Eczema

  • Loose stools

  • Nappy rash

The presence of symptoms after eating a food that you are intolerant to is dose dependent. This means that a small amount of a food high in food chemicals may not be enough to cause a reaction straight away. However, eating a large amount that goes over your individual threshold can cause a reaction. Since these chemicals are found in many different foods they can accumulate in the body over time. Therefore, eating small amounts regularly can lead to symptoms occurring after a few days.

The image below from the Royal Prince Alfred Hospital (RPAH) Allergy Unit is a great visual representation showing how these chemicals can gradually build-up until they exceed our threshold.

Dose Dependency Image

Management of Food Chemical Intolerance

Management is dependent on your individual threshold to these food chemicals. Those with a low threshold are recommended to avoid large doses of these and are often required to follow a low chemical diet. However, those with a higher threshold may only need to avoid meals containing high levels of these chemicals but can still eat small amounts.

How an Elimination Diet Can Help

An elimination diet is important in the diagnosis of food intolerances as, unlike allergies, there are no skin tests or blood tests that can be used. Trying to eliminate foods or food chemicals one at a time can often lead to unclear results as to which foods or chemicals are actually triggering your symptoms.

Determining the dietary triggers to your food intolerances is incredibly important. This will allow you to know which foods you can and cannot eat safely and which foods are likely to trigger your symptoms. It will also allow you to avoid unnecessarily restricting foods from your diet.

The only reliable and effective way of determining which natural food chemicals are triggering your symptoms is to eliminate all of these at one time and wait for your symptoms to settle. This can be a big adjustment to your current diet and eating habits and may seem difficult and overwhelming at first. You may feel that meals times become more complicated or that eating out is no longer fun. However, you can take a deep breath and relax! There are so many easy strategies that an Accredited Practising Dietitian (APD) who specialises in food intolerances, such as myself, will be able to provide you with so that you can still enjoy your activities and have pleasure from eating.

It is very important to remember that an elimination diet should only be completed under the supervision on an APD and only for a short amount of time. This is due to the fact that people following a restrictive diet, such as an elimination diet, are more at risk of nutrient deficiencies. An APD will provide you with appropriate 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.

When Should You Consider an Elimination Diet?

Food chemicals are believed to exacerbate and cause gut symptoms in some people with IBS due to their guts being more sensitive.

A low food chemical elimination diet is usually recommended to be trialled in those that have tried the low FODMAP diet and found that it did not give them a significant improvement in their symptoms. It also recommended for those who experience additional symptoms other than just in their gut.

The FODMAP diet is a therapeutic diet and is often used and recommended in the medical management of those with IBS. This diet helps to determine if these carbohydrates are responsible for triggering symptoms in those with IBS. To learn more about IBS and the FODMAP diet you can read my “Identify Your IBS Type To Find Fast Relief From IBS” and "FODMAP Diet Phase 1-3: The Journey Towards Managing Your IBS" blogs.

Whereas an elimination diet aims to identify if a person’s symptoms are triggered by chemicals found in foods, rather than carbohydrates. So, they focus on quite different food components. Some foods low in natural food chemicals are also high in FODMAPs, so although FODMAPs and food chemicals can cause similar symptoms, it can sometimes be difficult to determine which elimination diet is the most suitable.

The low FODMAP diet is recommended to be trialled first as it is less restrictive and are more likely to trigger IBS symptoms. Studies have shown that a low FODMAP diet can improve gut symptoms in up to 75% of people with IBS. However, as mentioned above, if symptoms are still being experienced, then the low chemical elimination diet is recommended for IBS.

The RPAH Elimination Diet

The RPAH Allergy Unity have developed an elimination diet specifically used for the investigation and management of suspected food intolerances. There are 4 stages of the RPAH elimination diet protocol.

Stage 1: Elimination Diet

The elimination diet is followed for at least 2 weeks. However, symptoms may take up to 6-8 weeks to settle. This phase of the diet requires people to avoid any foods high in natural food chemicals and substitute these with low natural food chemical alternatives.

There are 3 possible approaches to this stage of the diet. These include a strict, moderate or simple approach and your dietitian will discuss which approach is most suitable for you.

Restricting high food chemical foods enables us to determine if someone is responding to the low food chemical diet and whether it is resulting in a decrease in their symptoms. Once someone has had at least 5 days in a row free of symptoms they can begin the food challenge stage of the diet.

Stage 2: Challenges

This stage involves the challenging or reintroduction of each of the food chemicals in a systematic way that is well planned to ensure that the results you get are clear and accurate. During this stage people continue to follow the low food chemical diet as their base diet, with each food chemical group being challenged one at a time. A dietitian will give advice and guidance on which food to use for challenging, the order to reintroduce them and also the amount. This stage helps to determine which food chemicals may be triggering a person’s symptoms.

Stage 3: Liberalisation

STEP 1 – Personalised Diet

This stage usually lasts at least 3-4 weeks and is where the food chemicals that a person did not react to are added back into their diet based on the results from their challenges. During this stage people continue to avoid food chemicals that they reacted to.

STEP 2 – Identifying Tolerance Thresholds

A person moves onto this step when they feel comfortable with their personalised diet. This step involves testing a person’s threshold for each of the food chemicals that they reacted to, to determine the amount of a food chemical that they can tolerate before getting symptoms.

This is a particularly important part of the diet as it will identify whether a person may be able to tolerate a low, moderate or high amount of a food chemical before getting symptoms.

Stage 4: Long-Term Management

This is where different food chemicals are added back into the diet based on person’s individual tolerance. This stage is a particularly important phase of the diet as it enables us to develop a long-term balanced diet to ensure people are able to maintain and improve their overall health and quality of life.


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. Australasian Society of Clinical Immunology and Allergy (ASCIA). Food Allergy [Internet]. Cited 2019 May 28. Available from:

  2. Australasian Society of Clinical Immunology and Allergy (ASCIA). Food Intolerance [Internet]. Cited 2019 May 28. Available from:

  3. Barrett JS & Gibson PR (2012). Fermentable oligosaccharides, disaccharides, monosaccharides and polyols (FODMAPs) and nonallergic food intolerance: FODMAPs or food chemicals? Therapeutic Advances in Gastroenterology. 5(4):261-8.

  4. Perry CA, Dwyer J, Gelfand JA, Couris RR, McCloskey WW (1996). Health effects of salicylates in foods and drugs. Nutrition Review. 54(8):225-40.

  5. Royal Prince Alfred Hospital, Allergy Unit (2011). RPAH Elimination Diet Handbook with Food & Shopping Guide.

  6. Royal Prince Alfred Hospital, Allergy Unit (2016). Food Challenge Instructions Booklet.

  7. Royal Prince Alfred Hospital, Allergy Unit. The Role of Natural Salicylates in Food Intolerance [Internet]. Cited 2019 October 12. Available from:

  8. Skypala IJ, Williams M, Reeves L, Meyer R & Venter C (2015). Sensitivity to food additives, vaso-active amines and salicylates: a review of the evidence. Clinical and Translational Allergy. 5:34.


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