Food Intolerance

Frequently Asked Questions

This document has been developed by ASCIA, the peak professional body of clinical immunology/allergy specialists in Australia and New Zealand. ASCIA information is based on published literature and expert review, is not influenced by commercial organisations and is not intended to replace medical advice.

For patient or carer support contact Allergy & Anaphylaxis Australia or Allergy New Zealand

ASCIA PC Food intolerance FAQ 2024214.93 KB

Q 1: What are food intolerances?

Food intolerances describe a wide range of adverse reactions to foods. Food intolerances are sometimes confused with food allergy but do not cause allergic reactions. Food intolerances:

Involve the gastrointestinal system (gut). Food allergies involve the immune system.
Do not cause anaphylaxis which is a severe allergic reaction that can be life threatening (except for sulfite and benzoate reactions).

Non-IgE mediated food allergies are sometimes called food intolerances. These food allergies are different to food intolerances as they involve the immune system.

Q 2: What are the types of adverse reactions to foods?

Adverse food reaction

Food allergies are different to food intolerances, as shown above. Food intolerances include:

Metabolic conditions such as lactose intolerance (caused by a lack of lactase enzyme) and carbohydrate malabsorption (where the body doesn’t absorb certain sugars properly).
Chemical sensitivity (also known as pharmacologic reactions) to chemicals in foods like caffeine, monosodium glutamate (MSG), and other naturally occurring food chemicals like salicylates and amines.
Toxic reactions such as food poisoning and scombroid fish toxin.
Adverse reactions to artificial preservatives such as sulfites (often used in dried fruits) and benzoates (often used in soft drinks) have been shown to cause symptoms. These preservatives have also been reported as triggers for asthma and anaphylaxis.

Q 3: What symptoms do food intolerances cause?

Symptoms caused by food intolerance can affect the:

Gut causing bloating, gas/flatulence, irritable bowel syndrome (IBS), diarrhoea, constipation, and stomach pain.
Nervous system causing headaches, migraines, and fatigue.
Skin causing rashes, eczema, hives (urticaria), swellings, and mouth ulcers.
Airways causing an itchy, runny nose and increased mucus in the sinuses.

Q 4: What natural substances in foods cause food intolerances?

Foods contain proteins, carbohydrates, fats, nutrients, and many natural chemicals. Some naturally occurring substances add flavour and smell to food, but they can trigger symptoms in some people:

Lactose is a sugar found in cow’s milk and other dairy products. Lactose intolerance is an enzyme deficiency where people don’t have enough lactase enzyme to break down lactose in their diet. These people can get bloating, gas/flatulence, stomach upset, and diarrhoea after having dairy products. Lactose intolerance is uncomfortable, but not dangerous.
Monosodium glutamate (MSG, additive numbers 621-625) is added to some foods to enhance flavour. Glutamates also occur naturally in foods such as camembert cheese, Parmesan cheese, tomatoes, soy sauce, and mushrooms. MSG can cause a range of symptoms.
Vasoactive amines include tyramine, serotonin, and histamine. They are naturally found in pineapples, bananas, baked meat, vegetables, red wine, wood-matured white wine, avocados, chocolate, citrus fruits, and mature cheese. Amines can cause small blood vessels to expand, and they can trigger flushing, migraines, and nasal congestion in some people.
Salicylates are natural aspirin-like compounds that are found in many herbs, spices, fruits, and vegetables. Reactions to salicylates may be even more common than reactions to artificial colours and preservatives. Salicylates can worsen hives in some people.
Toxins can cause severe symptoms. When food spoils, it can become contaminated with bacteria or other micro-organisms (germs) which produce toxins. When people eat foods with high enough levels of these, they can get food poisoning. For example, if some types of fish are stored poorly, bacteria in the fish convert histidine to histamine. This can cause allergy-like symptoms in people who eat spoiled fish.
Irritants such as caffeine and curry can trigger indigestion in some people. Reactions to these irritants is not due to allergy.

Q 5: How are food intolerances diagnosed?

Food intolerances can often be difficult to diagnose as symptoms can depend on the substance and amount eaten. Diagnosis should be based on clinical history, response to treatment, and testing. Skin prick tests or blood tests for allergen specific IgE are negative for food intolerances. These tests can help diagnose food allergy.

If you think you have a food intolerance, your doctor can help to:

Make a diagnosis, such as migraines, hives, IBS, or recurrent mouth ulcers.
Check for other conditions that may be causing symptoms.
Determine if diet or other factors are causing symptoms.
Identify individual triggers to be avoided.

Q 6: Why are temporary eliminations diets used for food intolerances?

Once someone is diagnosed with food intolerance, looking at their clinical history can help identify the role of diet or other factors that make symptoms worse:

Temporary elimination diet: the only reliable way to determine if diet is playing a role is being placed on a temporary elimination diet, under the supervision of a dietitian and medical practitioner. If removing the food from the diet helps, this is followed by re-introducing the food under controlled conditions to identify food triggers which may need to be avoided in the future.
It is important that elimination diets are temporary, so they should only be undertaken for a short-term trial period, under medical supervision, as a diagnostic tool. Restricted diets that go for a long time can lead to problems with good nutrition, especially in children.
Low salicylate and low amine diets should not be used for the investigation of food intolerance until other potential causes for reactions are explored.

Q 7: Can unorthodox tests be trusted?

Some people use unorthodox methods for diagnosing health problems. Several misleading tests have been promoted for diagnosing food allergies and intolerances, without any credible evidence, and at significant expense as these tests are not rebated.

These tests include cytotoxic food testing, vega testing, kinesiology, allergy elimination techniques, iridology, pulse testing, alcat testing, Rinkel's intradermal skin testing, reflexology, hair analysis, and IgG food antibody testing. They have been shown to be inaccurate and unreliable in published studies. Treatment based on inaccurate results can result in ineffective and sometimes harmful treatments and delay the proper management of food allergies and intolerances.

Q 8: What are other adverse reactions to food?

There are many other adverse reactions to foods, apart from allergies and intolerances, including:

Feeling unwell after eating due to heartburn after a fatty or spicy meal, or a hangover after too much red wine.
Coeliac disease is not an allergy but does involve an immune system response to foods containing gluten. When gluten-containing cereals (like wheat) are eaten, inflammation of the gut occurs, resulting in poor absorption of nutrients. Major symptoms are gut upset, fatigue, anaemia, or weight loss.
Non-coeliac gluten intolerance is a recently recognised condition which can cause symptoms such as abdominal disturbance (usually bloating but sometimes other symptoms as well), and occasionally discomfort and tiredness. It appears to be genuine as proven by blinded challenge studies, but the mechanism is not known.
Food aversion is a condition where a person not only dislikes a food, but also experiences unpleasant physical symptoms when they see or smell the food. Symptoms are triggered by emotions associated with food rather than the food itself. This does not usually occur if the food is disguised.

Underlying anxiety can result in unconscious over-breathing or hyperventilation. The symptoms that result (dizziness, tight chest, blurred vision, or numbness) can be very distressing, and can sometimes resemble food allergy.

Content updated August 2024

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