Food Intolerances Explained

True Protein Blog Avatar Fallback reviewed by our Nutrition Team 23 November 2020

Gluten intolerance, IBS, lactose intolerance - whether you’re someone who frequently experiences unmanaged gut symptoms or just want some general information around food intolerances, this whistle stop tour is for you!

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Food Intolerances Explained

Self-prescribed food avoidance from suspected intolerance commonly plays out among the growing number of young, health conscious Australians. Unwanted symptoms stemming from intolerances such as gas, bloating, diarrhoea, constipation, pain and cramping may improve or resolve by practicing food avoidance, which (in the short term) is fantastic for increasing quality of life. On the other hand, cutting out foods or entire food groups without the supervision of a General Practitioner (GP) or Accredited Practicing Dietitian (APD) can sometimes do more harm than good long term. The insight below is no replacement for professional guidance but does provide an overview of what food intolerances are and why they occur.

Both food intolerances and food allergies fall into the 'adverse food reactions' category and have overlapping symptoms which are commonly looked at in research. It is important to consider that although some symptoms may be similar, intolerances and allergies are adverse food reactions with vastly different mechanisms, diagnostic measures and interventions.


Food allergies differ from food intolerance in that they are mediated by our immune system and can be life threatening, like what we see in anaphylaxis, for example. If you experience symptoms such as hives, skin rash, vomiting, diarrhoea, agitated skin, swelling of the tongue, lips, face and/or eyes, and difficult breathing, then visiting a GP (or calling 000 if urgent) is highly recommended.


On the other hand, food intolerances are not mediated by our immune system – instead they are related to the body struggling to digest, absorb or utilise a component of a food. The part of the body responsible for these functions is known as the gastrointestinal (GI) tract which includes the mouth, oesophagus, stomach, small intestine, large intestine and anus. Each section has a different role, with the small and large intestine being most (but not the only) affected in food intolerances as they are the main site for absorbing the food we eat.


Causes of Food Intolerances

We can be intolerant to a food or food component for a range of reasons such as (Mahan & Raymond, 2017):

  • Toxicity and microbial contamination – like when your bread grows mould

  • Drug/additive - some individuals may have trouble digesting or metabolising caffeine or food additives

  • Psychological and behavioural - our gut and brain 'talk' to each other so when psychological issues arise such as anxiety, it can impact the way in which our digestive system functions

  • Genetics

  • Gastrointestinal disorders

  • Unknown causes


Among the most common of these are gastrointestinal disorders which include irritable bowel syndrome (IBS), lactose intolerance, irritable bowel diseases (IBD) such as Crohn’s disease and ulcerative colitis, and others. The latter require rigorous medical treatment whereas the former can be well managed through diet and lifestyle alone. With this background in mind, let’s have a look at a few different types of food intolerances managed through diet and lifestyle interventions.


Lactose Intolerance

Lactose is the sugar naturally found in some dairy products, and lactase is the enzyme that breaks down and digest it. Intolerance to lactose develops due to lactase enzyme deficiency manifesting due to genetics or decreased dairy consumption over time.

The abundance of lactose free dairy alternatives found on supermarket shelves is a fair indicator of the prevalence of lactose intolerance, whether it is self-diagnosed or not. Contrary to popular opinion that lactose is found in all dairy, high amounts of lactose are mostly found in milk, ice-cream, cottage cheese, some yoghurt and custard. Whereas, fermented dairy products such as parmesan, brie, camembert, feta and cheddar are naturally low in lactose, so even those with intolerance can often enjoy them without experiencing severe symptoms. Despite being derived from cows milk, True's WPI90 only contains trace amounts of lactose, having had most of it stripped away during filtration. For a protein formula completely free from lactose, try Collagen or Vegan85

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Potential symptoms of lactose intolerant include abdominal pain, diarrhoea and/or gas and may arise on an individual basis according to amount of lactose consumed. It is vital to consider that dairy is a food group in itself which contains energy, protein, calcium, phosphorus and other nutrients which benefit our overall health. Thus, excluding all dairy due to lactose intolerance rather than just looking for low lactose or lactose free versions may leave nutritional gaps and health consequences.


Irritable Bowel Syndrome (IBS)

Unlike IBD, IBS is not an inflammatory disease nor a food intolerance, but rather a condition of functionality leading to a range of potentially debilitating symptoms such as gas, bloating, constipation, diarrhoea, and abdominal pain. These symptoms come from altered muscle contractions of the GI tract which ‘squeeze’ food along (think of a tube of tooth paste), overly sensitive nerves in the intestines, and disharmony between the gut and brain (anxiety, for example, can negatively impact how the gut functions). IBS is extremely common, so if you have been diagnosed it may bring comfort knowing that about 20% of Australians experience the symptoms of IBS at some time during their life. Need more comfort? IBS does not directly lead to internal damage or severe health problems (Gastroenterological Society of Australia, 2010).


If you suspect or have been diagnosed with IBS, it is highly recommended you see an APD who is trained in identifying triggers and managing symptoms using a range of tools. Although food may be the trigger of IBS, it is not always the case as infection, stress and anxiety, medications, physical activity and general dietary patterns also factor in.

Going into first and second line interventions is beyond the scope of this article, however, the take home message is that once you and your APD have identified the specific types of foods which trigger symptoms (and ruled other potential culprits such as medications, fluid intake, meal frequency, and medical conditions like coeliac disease out), it is paramount to introduce the ones that don't back into your diet. This is because common foods which contribute to IBS include fruits, vegetables, nuts and dairy - all of which offer a broad spectrum of vital nutrients that contribute to your overall health. Striving for 30 different plant-based foods per week ensures you are maintaining a well-rounded diet. And yes: it is absolutely possible to do this once you know the exact foods/food types contributing to your symptoms.



One food component which is commonly blamed for gastrointestinal upset is gluten, a protein found in barley, rye, sometimes oats and wheat (remember – BROW). Gluten free diets are a hot topic in Western culture, with almost twice as many google search results as low carb diets (which are not commonly recommended).

Following a gluten free diet is typically the case in three scenarios

  • coeliac disease

  • non-coeliac gluten sensitivity - diagnosed when symptoms persist despite coeliac disease being ruled out after testing OR

  • adhering to societal trends with the false belief that going gluten free is "healthier"


As coeliac disease is an autoimmune condition which damages and inflames the small intestine upon every exposure, it is the only of the three scenarios where a strict gluten free diet is necessary. It is highly recommended that you visit a GP to commence screening for the condition if you have recently lost weight, feel fatigued, bloat, experience stomach cramps, and/or diarrhoea after consuming gluten-containing foods. If you have been diagnosed, looking for the certified Gluten Free logo on food labels and downloading mobile apps like FoodSwitch to help identify gluten free products can be useful tools to ensure gluten is eliminated completely.


There is debate to whether another condition known as non-coeliac gluten sensitivity exists, however, overwhelming anecdotal evidence suggests it does. Self-diagnosed non-coeliac gluten sensitivity is frequently seen because some individual’s symptoms improve when commencing a gluten free diet. This is a great thing and trialling small portions of barley, wheat, rye and/or oats is ok to test how much can be tolerated, provided the person has returned negative for coeliac disease.

Some gluten-containing foods such as wheat contain other nutrients like fructans. These fructans are sometimes the culprit to their IBS-like symptoms as opposed to gluten, leading to the false belief that they’re sensitive to all gluten-containing products. As a result, they might be blindly and unnecessarily restricting their diet without knowing the underlying trigger.


Avoiding gluten without Coeliac Disease?

Sometimes people might avoid gluten even without these symptoms because they believe following a gluten free diet is healthier. If you genuinely feel better avoiding barley, rye, oats and wheat and it does not interfere with your lifestyle and diet quality (providing you are consuming other grains like rice and quinoa), then this is completely fine. However, if the sole reason for this is because celebrities, testimonials and books validate avoiding gluten for health reasons -then stop right there.

Social media and advertising likely explain why despite less than 1% of the population have a coeliac disease diagnosis, sales of gluten free products more than doubled from 2011 to 2016 (Niland & Cash, 2018). Among all this noise are the forgotten health benefits that come with consuming barley, rye, wheat and oats in the absence of their related conditions. These include fibre for gut and heart health, carbohydrates and energy which fuel an enjoyable and active life, vitamins and minerals to ensure bodily processes are working and one thing that is especially forgotten – the fact that they can be a component of a delicious, healthy meal with no adverse health outcomes for the otherwise healthy person.

Moreover, needlessly purchasing gluten-free products is an expensive exercise from both a financial perspective and nutrition quality perspective - just because they don’t contain gluten does not mean they are automatically ‘healthier’.



Having an understanding of how food intolerances impact thoughts and behaviours will empower you to make informed dietary choices. While food allergies require complete avoidance of triggers for potentially fatal medical reasons, intolerances just require strategic planning and managing of symptoms. While it is completely understandable that some turn to cutting out foods and food categories, there are better ways around this which enable a less restricted, enjoyable lifestyle. If you feel as though your symptoms are not improving, it may be worthwhile visiting a health professional to regain some control of your symptoms, diet and lifestyle.


Useful Links



  1. Gastroenterology Society of Australia. (2010). Irritable Bowel Syndrome (IBS). Digestive Health Foundation

  2. Mahan, K.L. & Raymond, J.L. (2017). Krause’s Food & The Nutrition Care Process (14th ed). Elsevier

  3. Niland, B. & Cash, B. (2018). Health Benefits and Adverse Effects of a Gluten-Free Diet in Non–Celiac Disease Patients. Gastroenterology & Hepatology, 14(2), 82 – 91

IMPORTANT INFORMATION: all content provided here is of a general nature only and is not a substitute for individualised professional medical advice, diagnosis or treatment and reliance should not be placed on it. For personalised medical or nutrition advice, please make an appointment with your doctor, dietitian or qualified health careprofessional.