Food Allergy Diagnosis - Part 1

Dr. H. Steinman



This article on Food Allergy Diagnosis provides food allergic subjects and the parents of food allergic children with accurate scientific information that is in agreement with the viewpoint expressed by the Sub-Committee on Adverse Reactions to Foods of the European Academy of Allergy and Clinical Immunology (EAACI). This statement is therefore authoritative and fully in line with modern conventional medical theory and practice.

Adverse reactions to foods is a very complex topic, and this brochure can only provide the barest overview for the patient. Further reading is strongly recommended.



Up to 20% of the general population believe they have an adverse reaction to one or another food. However, scientific studies have shown that the true figure lies around 1%. However, in certain populations, such as children, the true incidence may be 7%, and up to 10% for patients who have other symptoms of allergy.



Food allergy is just one of several different forms of adverse reactions to foods. The classification of Food Adverse Reactions is important to avoid misunderstandings and when considering the cause of the symptoms, the mechanism of the symptoms, and the optimal therapy.

1. Food Allergy
There are two different types of food allergic reaction involving the body's defence (immune) system. The term "food allergy" should be reserved only for these types of reactions.

  • IgE-mediated
    A food allergen is the part of a food, usually a protein that stimulates the defence (immune) system of the person to produce IgE antibodies against that specific food.
  • Non-IgE-mediated
    With this type of reaction, the immune system produces antibodies against the food that are not IgE, but of some other type.

2. Toxic Food Reactions
This is a natural reaction to eating a food that contains naturally occurring toxins, such as poisonous mushrooms, or toxins that develop due to contamination of the food by, for example, bacteria or moulds (aflatoxins).

3. Food Intolerance
The definition "food intolerance" is used when the history and/or the provocation tests clearly prove a food is the cause of the symptoms, but there is no evidence that the defence (immune) system is involved. Food intolerance can be caused by various chemicals present in the food that themselves directly cause an effect on the body.

Examples are:

  • Enzymatic Food Intolerance, such as "Lactase Deficiency"
  • Pharmacological Food Intolerance, such as the histamine, tyramine, serotonin naturally found in foods such as cheese, tuna, alcoholic beverages, etc.
  • Undefined Food Intolerance, such as an intolerance to food additives such as:
    • (i) food colourings such as tartrazine and other azo dyes,
    • (ii) food flavourings such as MSG and aspartame,
    • (iii) food preservatives such as sulphites and benzoates,
    • (iv) food anti-oxidants, such as BHA and BHT.

4. Food Aversion This is a psychological condition often caused by a previous adverse reaction (for whatever reason) so that the person convinces himself or herself that they will react to that food on a subsequent exposure.


IgE-Mediated Food Allergy

The IgE antibodies produced by the defence (immune) system are directed against certain proteins in the food, for example proteins that are found in egg white, cows milk or protein. The IgE antibodies are attached to a special type of cells called mast cells. The reactive parts of the IgE antibodies then bind with the proteins on the food substance that is circulating in the blood. When a protein has two or more IgE antibodies attached to it and they in turn are attached to the mast cell, then a bridging reaction occurs. The mast cell is then stimulated to release biologically potent chemical substances, called mediators. Histamine is the best known of these mediators. These in turn have an immediate and then a delayed effect on the surrounding cells, the result of which is intense swelling, muscle spasm of the walls of the affected organ, and the production of watery mucus. These reactions can occur not just in the gut where the food is absorbed, but in almost any tissue of the body where the blood has carried these food proteins.

Although IgE mediated food allergy represents only approximately 20 to 40% of all cases of adverse reactions to foods, this figure may climb to well over 50% in certain medical situations, such as newborns and infants being exposed to new foods, or infants and children developing eczema and / or urticaria due to a food adverse reaction. It is also important to note that IgE-mediated food allergy is most usually the easiest type of food adverse reaction to diagnose and the easiest to identify the offending food. This is partly because the symptoms are usually more immediate after the ingestion of the food, and partly because the diagnostic tests used are readily available and reasonably reliable. For these reasons, when a doctor is confronted with a patient who presents with symptoms of possible food adverse reaction, the doctor will usually consider food allergy first and will utilise the appropriate tests for the diagnosis of food allergy and the identification of food allergens.


Symptoms of Food-Allergic Reactions
IgE-mediated allergic reactions to foods normally start within a few minutes of the ingestion of the food, though it can take hours. For some very sensitive individuals, the reaction may appear immediately the food is even touched to the skin or even inhaled. Usually symptoms appear in combinations, involving different organ systems such as the skin, the gut and even the nose and the lungs.

  • G-I Tract: Oral Allergy Syndrome, infantile colic, cramps, nausea, vomiting, diarrhoea
  • Respiratory Tract: allergic rhinitis, larynx oedema, allergic asthma
  • Skin: urticaria, angioedema, atopic dermatitis, contact dermatitis.

The most severe reaction is anaphylaxis. In this case, the sudden release of the multiple chemical mediators results in severe itching, hives, swelling of the throat, broncho-constriction, lowered blood pressure, unconsciousness and sometimes-even death. This sequence of events is fortunately rare but should be borne in mind by any person who is very sensitive to any food. The foods usually associated with anaphylaxis are peanuts, tree nuts, seafood, eggs and milk. Persons with this condition must be able to inject themselves with epinephrine (adrenaline) and know when and how to use anti-histamine drugs. These persons should always carry a Medic Alert bracelet.

There are occasionally other symptoms, which are blamed on an adverse reaction to a food. However, there is no conclusive evidence that adverse reactions to food cause drowsiness, hyperactivity, chronic fatigue syndrome, migraine, rheumatic symptoms, etc. However these cases are rare, and in most cases cannot be proven or do not stand up to scientific clinical study.

Coeliac Disease
CD is intolerance to foods containing gluten, such as cereals. CD affects both children and adults. Typical symptoms in children are weight-loss, failure to thrive, and anaemia. The diagnosis is made by measuring the presence of IgA and / or IgG anti-gliadin antibodies, and confirmed by an intestinal biopsy and the success of a gluten-free diet.


Cross Reactivity
Sensitisation to a certain food, such as a vegetable or a plant or a nut, is often associated with sensitisation to other foods belonging to the same or a closely related botanical family. Classical examples are peanuts and other legumes such as soya bean; apple and pears; watermelon and tomato, peach apricot, plum and cherry, etc.

Another type of cross-reactivity is that exhibited between foods and various inhalant allergens. This is perfectly understandable as, for example, wheat is a grass and so a person sensitised to wheat will also react to inhalation of certain related grass pollens. In addition, once a person has been sensitised to a food, and this is most usually a baby, infant or child, then as the patient grows older the switched-on IgE system will produce antibodies against other inhalant allergens such as cats and dogs, house dust mite, and pollens. This patient then shows symptoms of allergy against these inhalant allergens.

An increasingly recognised sensitisation is against latex rubber, with a simultaneous sensitisation against the foods kiwi fruit, pineapple and banana. Deaths have been reported from this sensitisation, as well as many cases of occupational disability due to eczema symptoms from the latex allergy.


Foods that may trigger a Non-Immunological Reaction
Many different foods contain the histamine, or serotinin, or other chemicals which are also the mediators normally released by mast cells triggered by an IgE-allergen bridging reaction. These may have direct or indirect effects on the vascular system. Histamine may cause symptoms like headache, diarrhoea, or a rash. Tyramine and phenylethylamine are reported to trigger migraine headaches.

Examples of these foods are:
Alcohol - histamine liberators
Aubergine - histamine
Avocado - vasoactive amines
Banana - serotonin, histamine
Beans (unboiled) - lectins, hemagglutins
Beer - tyramine, sulphites, histamine
Cheese - histamine, tyramine, phenylethylamine, mould toxins
Citrus fruit - vasoactive amines, tyramine, chlorogenic acid
Cocoa / chocolate - histamine liberators, phenylethylamine
Coconut - mould toxins
Egg white - histamine liberators
Fermented food - vasoactive amines
Grains - histamine liberators, mould toxins
Herring - histamine
Fruit juices - tartrazine
Mackerel - histamine
Nuts - mould toxins
Pork - histamine liberators
Salami sausage - histamine, tyramine, sodium nitrate
Shellfish - histamine liberators
Soy bean - mould toxins
Strawberry - histamine, histamine-liberators, aromatic substances
Tomato - vasoactive amines
Tuna fish - histamine
Wine - histamine, sulphur dioxide, chemical additives


Hidden Food Allergens

It is particularly important for children and adolescents to be aware of hidden allergens in different foods, as this group is especially vulnerable to commercially prepared foods where the risk of hidden allergens is greatest. It is therefore important for food sensitive patients to read and understand food labels. Unfortunately some labels are inaccurate, misleading or incomplete. Therefore it is important for these persons to be able to manage any severe or even anaphylactic reaction that may occur to a hidden food allergen.

Hidden AllergenFood
Peanut - peanut butter, peanut oil, pastry, candy, nut mix, cereals
Milk - sorbet, Cremora, margarine, sausages
Soya bean - hamburgers, mince meat, hot chocolate, milk substitutes
Cereals - snack foods, processed meats, ice cream, soup mixes
Egg - pasta, meatballs, macaroni, lemon curd, soups
Casein - butter substitute, sausage, canned fish, candy, meats
Yeast - bakery products, beer, mayonnaise, ketchup
Antibiotics - cow's milk, beef, pork

Part 1 | Part 2


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