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What is the difference between an allergy and intolerance?

A true food allergy causes an immune system reaction that affects numerous organs in the body. It can cause a range of symptoms including difficulty breathing, exhaustion, headaches, migraines, itchy skin, hives, furry tongue, blurred vision, pain and digestive issues. In some cases, an allergic reaction to a food can be severe or even life-threatening.

In contrast, a food intolerance is generally less serious and often limited to digestive issues (symptoms such as bloating, flatulence, abnormal bowels, cramping, reflux etc). In the case of a food intolerance, individuals may be able to eat small amounts of the offending food without trouble. In addition, the intolerance may be prevented through taking supplements, for example digestive enzymes, where there is sugar malabsorption.

Food allergy = immune system reaction to a food

Food intolerance = inability to digest a food

Signs and Symptoms

Symptoms of Food Intolerances do not always just pertain to the gut.

symptoms of food intolerances.PNG

Diagnosis of a food intolerance


This should only be carried out by a trained Accredited Dietitian or Medical Practitioner (allergist/immunologist) skilled in the area of diagnosing food intolerances. Food intolerances cannot be diagnoses by a blood test, hair mineral analysis or other unorthodox test.

Read here about Unorthodox allergy and intolerance testing and treatments:

A skilled Dietitian or Allergist/Immunologist will conduct a thorough Sensitivity History of yourself and your family. They will then draw conclusions and determine if food intolerances are contributing to your symptoms. If you're seeing an Allergist, and they feel that food is a contributing factor, they will refer you to a Dietitian who specialises in Food Intolerances. The dietitian will decide which is the best diet for you, without compromising your nutrition. They may also prescribe nutritional supplements such as digestive enzymes or specific probiotics that research has proven to be effective in your situation. For successful long term management, the Dietitian will conduct Food challenges and teach you how to navigate dining out and travel.

Common intolerances we often see in our practice:


The sugar found in milk products. When there is a shortage of the enzyme lactase in the brush border of the small intestine an individual will not be able to digest and absorb lactose properly. Symptoms include bloating, flatulence, upset stomach, and diarrhea. These symptoms can be resolved by avoiding dairy foods, taking a digestive enzyme which contains the lactase enzyme at the same time as consuming diary foods, or choosing “lactose free” milk and yoghurt.


These are undigestible sugars which survive all the way to the large intestine and can cause a range of gut symptoms. Around 40% of people diagnosed with Irritable bowel syndrome (IBS) benefit from a low FODMAP diet. There is much confusing information about FODMAPS so it is important to do this under supervision of a Dietitian who has had training in this area.

Dairy milk casein protein

Casein A1 protein found in cow’s milk (except Jersey and Guernsey cows that produce A2) is indigestible in the human gut. Some individuals, most commonly children under the age of two years, react negatively to the ingestion of this protein. For such individuals, avoidance is necessary. If found to be a problem in young children, a food challenge later in life is worthwhile to assess whether tolerance has increased.

Food additives

Additives in processed foods most commonly linked to an intolerance include artificial colours (tartrazine 102, Quinoline yellow 104, Carmoisine 122, Brilliant Blue 133, Brown HT 155) flavours (Glutamates including MSG 620-625, Ribonucleotides 627, 631, 635) and artificial sweeteners (Acesulphame-K 950, Aspartame 951) and some preservatives (e.g. sulphites, benzoates).


These are preservatives commonly found in wine, dried fruit and naturally occurring in other foods. Their numbers are 220-228 and appear in the ingredient list. Sulphite reactions cause asthma, rashes, irritable bowel syndrome and headaches in sensitive people. Sulphur in medications and household products can induce severe, and sometimes immediate reactions. A Dermatologist can help diagnose allergic reactions to chemicals, metal and household products, particularly if you get a skin reaction (e.g. hives, eczema, rash).


A group of plant foods which in less than 0.5% of people can cause digestive issues, pain and headaches. It appears to be the lectin and the alkaloid parts of these plant foods which cause symptoms. 

Children and Food intolerances

Many children "grow out" of their food intolerance as their immune and gut system develops, so for many kids it is not necessary to avoid a allergen food for life. Some people with adult onset food allergies or intolerances may find the opposite happens, and that as they get older they need to be extra careful and seek extra dietary advice. In either case, regular visits to your dietitian and Immunologist can ensure that you are not unnecessarily avoiding foods, and that you continue to avoid or limit the ones that matter.

Reference/further reading

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