Food intolerance


IMPORTANT The information provided is of a general nature and should not be used as a substitute for professional advice. If you think you may suffer from an allergic or other disease that requires attention, you should discuss it with your family doctor. The content of the information articles and all illustrations on this website remains the intellectual property of Dr Raymond Mullins and cannot be reproduced without written permission.

Around 1 in 10 infants and 1 in 100 adults are allergic to food. Severe reactions result in difficulty breathing, severe rashes, swelling of the face or throat, dizziness, stomach upset or a drop in blood pressure (shock) and loss of consciousness. Other people complain of symptoms after eating like headaches, bloating or mouth ulcers that are not caused by allergies. Some of these result from enzyme deficiencies or food intolerance.

Allergic reactions to food are usually obvious
During an allergic reaction to food, irritant chemicals (like histamine) are released into the tissues. This can result in itchy rashes, stomach upset, cough and wheeze and the more serious symptoms of anaphylaxis. These reactions are due to an immune system reaction to foods. When people complain of symptoms like headaches, bloating or mouth ulcers after eating, they are not describing allergy, but rather intolerance. As these symptoms are not due to allergy, allergy testing is of little use and can sometimes be misleading.

Not all reactions to food are due to allergy
Feeling unwell after eating doesn't always mean that the meal was to blame, nor that allergy was the cause. For example, heartburn after a fatty or spicy meal is no more an allergy than a hangover after too much red wine. Coincidence sometimes plays a role too. After all, we spend many of our waking hours eating or drinking! Nevertheless, some unlucky people do suffer symptoms from food that are not due to allergy or overindulging.

What is food intolerance?
Food intolerance can be a difficult concept to understand. Sometimes substances within foods can increase the frequency and severity of migraine headaches, skin rashes (like hives) or the stomach upset of irritable bowel. It's not so much that these substances are the cause of symptoms, but rather that they aggravate an underlying condition. It's a bit like having a sore on your leg and you go swimming in salt water. The salt water makes it hurt more, but didn't actually cause the sore in the first place. The best approach is to first consult your doctor to:
1. Make a diagnosis (e.g. migraines, hives, irritable bowel, recurrent mouth ulcers);
2. Determine whether dietary (or other) factors play an aggravating role; and
3. Identify individual triggers to be avoided.

What conditions are associated with food intolerance?
The commonest conditions in which these diets are used include recurrent or chronic urticaria (hives), migraine headaches, irritable bowel syndrome, eczema and recurrent mouth ulcers. Less common reasons to consider diet manipulation include hyperactive behaviour (in young children) or chronic nasal congestion. Non-specific fatigue is NOT likely to respond to diet manipulation.

Fodmaps diets and stomach upset
Poorly digestible dietary sugar molecules such as fructans can trigger stomach upset in some people, and many with irritable bowel syndrome will respond to a so-called FODMAPS diet.

Natural food chemicals can sometimes trigger symptoms
Natural chemicals are found in the foods we eat. Food is composed of protein, carbohydrate, fat and various nutrients as well as a number of natural "chemicals". These naturally occurring molecules are often add flavour and smell to food. Sometimes they will trigger symptoms in unlucky individuals. It is important to realise that reactions to these substances are not due to allergy, and so allergy testing is of little use in helping us to decide what to avoid.
Monosodium glutamate (MSG, 620, 621, "flavour enhancer") ­ was originally isolated from seaweed in 1908 by a Japanese chemist. It also occurs naturally in such foods as camembert cheese, Parmesan cheese, tomatoes, soy sauce and mushrooms. MSG stimulates nerve endings, perhaps accounting for its function as a "flavour enhancer" amongst other properties.
Vasoactive amines such as tyramine, serotonin and histamine are well known triggers of migraines in some patients and are present naturally in pineapples, bananas, baked meat, vegetables, red wine, wood-matured white wine, avocados, chocolate, citrus fruits and mature cheese. Amines can act directly on small blood vessels to expand their capacity, perhaps accounting for their effect on flushing, migraines and nasal congestion in some patients.
Salicylates are aspirin like compounds (and aspirin was originally isolated from willow tree bark) present in a wide variety of herbs, spices as well as fruit and vegetables. Indeed, reactions to these may be even more common than reactions to artificial colours and preservatives. Aspirin can trigger hives (urticaria) by acting directly on skin mast cells. Natural and structurally similar salicylates can also worsen hives in some patients.
Toxins - Other than contamination of food with micro-organisms or their products (spoilage, food poisoning), some foods contain toxins than can cause severe symptoms. For example, if some types of fish are stored poorly, their gut bacteria can convert histidine to histamine, resulting in allergy-like symptoms.
Irritants - caffeine and curry are gut irritants and can trigger indigestion in some people.

Other adverse reactions to food
There are many other adverse reactions to foods, apart from allergy and intolerance, including:
Enzyme deficiencies - some people are born without enough enzymes to digest, absorb or deal with some foods. For example, a deficiency of the enzyme lactase results in lactose intolerance. The inability to digest lactose can result in bloating, wind, nausea and diarrhoea after having dairy products.
Alcohol dehydrogenase deficiency results in flushing and severe nausea because people with this enzyme deficiency are unable to metabolise toxic breakdown products of alcohol.
Coeliac disease ­ Celiac disease is not an allergy, but does involve an immune system response to food 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, and anaemia or weight loss.
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 than result (dizziness, tight chest, blurred vision or numbness) can be very distressing, and the symptoms can sometimes resemble food allergy.

Are allergy tests necessary? 
A diagnosis of adverse reactions to food is based on the history, response to treatment and testing where necessary. Allergy tests (Skin prick tests or CAP/RAST) are of little use unless the history suggests that allergy (as opposed to intolerance) is the problem.

Non-conventional tests can be misleading
Some adults and children in Australia and New Zealand use non-conventional methods for diagnosing health problems, including allergies. Unfortunately, a number of misleading tests have been promoted for diagnosing allergies, in the absence of any credible evidence of their reliability. Various methods such cytotoxic food testing (Bryans' test), Alcat testing, kinesiology, allergy elimination techniques, Vega testing pulse testing, reflexology and hair analysis have all been proposed as being useful for diagnosing allergic conditions. Not only do these tests lack any scientific rationale, but have been shown to be inaccurate and poorly reproducible when subjected to careful study. Treatment based on inaccurate results is not only misleading, but can result in ineffective and sometimes harmful treatments, and delay more effective therapy.

Temporary elimination diets sometimes can be useful
Once a diagnosis is made (e.g. migraines, hives, eczema, irritable bowel, recurrent mouth ulcers), the history may help identify the role of dietary or other factors in making symptoms worse. The only reliable way to sort out whether diet is playing a role is by people being placed on a temporary "elimination diet" under the supervision of a skilled dietitian and medical practitioner. If the diet helps, this is followed by challenges under controlled conditions to identify dietary triggers so that they can be avoided in the future. It is important to emphasise that "elimination diets" must only be undertaken for a short term, under strict medical supervision and only for very good reasons. Prolonged restricted diets can lead to problems with nutrition, particularly in children.

Additional information on Elimination Diets can be found in "Friendly Food", published by the Royal Prince Alfred Hospital Allergy Unit in Sydney.

Last reviewed 5 June 2020


Some people complain of symptoms after eating like headaches, bloating or mouth ulcers that are not caused by allergies. Some of these result from enzyme deficiencies or food intolerance. Allergy testing is no use in diagnosing food intolerance and unorthodox tests that claim to help diagnose intolerance are best avoided due to lack of reliability.