Food Allergy


The adverse reaction to food is a very complex matter and this summary can cover only the basics. Further reading is strongly recommended, especially if one is investigating a suspected reaction to food.

How Common Is Food Allergy?

Up to 20% of the general population believes that it has an adverse reaction to one food or another. However, scientific studies have shown that the true figure is closer to 1%. Yet, in certain populations, such as children, the true incidence may be 7%. It may be up to 10% for individuals who have other symptoms of allergy.

What Is The Difference Between Food Allergy And Other Adverse Reactions To Food?

Food allergy is just one of several different forms of adverse reactions to foods. It is important to keep all forms in mind when considering the cause of symptoms, the mechanism of symptoms, and the optimal therapy in any particular case.

  1. Food Allergy. There are two different types of food allergic reactions involving the body’s defence or immune system and the term “food allergy” should be reserved for these types only. They are:
    1. IgE-mediated:this is a reaction resulting from the release of an antibody called immunoglobulin-E (IgE), a substance which is produced by cells of the body’s defence (immune) system in response to an allergen which has entered the body. A food allergen, usually a protein, stimulates the immune system of an allergic individual to produce IgE antibodies against that specific protein, thinking that the protein may be harmful. IgE antibodies can result in very rapid allergic reactions, including skin rashes, asthma, symptoms of food allergy, and shock. Blood tests can confirm whether an allergy is of this type.
    2. Non-IgE-mediated:this is a reaction by cells of the body’s defence (immune) system in response to an allergen that does not trigger the production of immunoglobulin-E. This often results in delayed allergic reactions that may take some hours to a few days to develop. Allergy as a result of non-IgE cannot easily be confirmed by blood tests.
  2. Toxic Food Reactions. These are reactions to eating foods that contain naturally occurring toxins, such as poisonous mushrooms, or toxins that develop due to contamination of the food by, for example, bacteria or moulds (which may produce substances such as aflatoxins).
  3. Food Intolerance. The term “food intolerance” is used when the history and/or the provocation tests clearly prove that a food is the cause of the symptoms but there is no evidence that the immune system is involved. The adverse reactions often occur as a result of the body being partially or completely deficient in a substance, an enzyme, which is required to break down a particular substance in the food.One example is the reaction to lactose, the naturally occurring sugar in milk, which a large portion of the world’s adult population cannot digest. “Lactose intolerance” is therefore a rather common condition, though hidden in many cultures because of very limited use of dairy products.

Other causes of food intolerance are the various non-allergenic substances present in food that can act as “drugs” and thus directly or indirectly cause an effect on the body. An example of this is caffeine which is found in coffee or chocolate – it can result in an increased heart rate, trembling, irritability, or in keeping one awake.

  1. Food Aversion. This is a psychological condition, often caused by a previous adverse reaction of some kind. The subject believes himself or herself to be at risk of, or even suffering from an adverse reaction, but there is no proper biological basis for this belief. One example (among many) would be of an individual reacting to the tomato in a marinara sauce but mistakenly believing that the reaction was due to the shellfish that it was being eaten with. The person may subsequently have so much anxiety about shellfish that he or she not only has an aversion to it, but may even manifest symptoms upon ingesting it.

How Are Food Allergies Diagnosed?

Diagnosis of an adverse reaction to a food is easy if the subject consistently and immediately exhibits the same symptoms after eating the food. However, diagnosis is usually more challenging, as 1) an individual could be reacting to more than one food, 2) there may be a time delay before the onset of symptoms, and 3) many symptoms can have causes other than an adverse reaction to a food.

A given food can cause symptoms that differ from person to person. The range of an individual’s symptoms to a given food may also differ from occasion to occasion. It is therefore important for a patient who believes that he or she is suffering from an adverse reaction to a food to consult an allergist or other suitably qualified and experienced specialist doctor. Such a specialist can determine whether the symptoms are indeed related to a food, or whether there is some other cause.

Long-term dietary changes and guidelines are justified only after a proper diagnosis has been made according to accepted, mainstream medical practices. In children, the diagnosis should normally be considered temporary and re-evaluated at intervals as the very young can “outgrow” many food allergies. For milk and egg allergy, this re-evaluation should be done yearly, whereas peanut allergy is usually a life-long condition. However, while one food allergy or group of food allergies can disappear, other food allergies may emerge. Furthermore, different types of allergy symptoms can develop, and sensitisation to other categories of allergens such as house dust mites, grass pollens, cats and dogs (which are inhalant allergens) can arise.

How Food Allergies Should Not Be Diagnosed

Diagnostic and treatment methods used by “clinical ecologists” on patients with an alleged environmental illness (also known as food and chemical sensitivity, environmentally induced disease, ecologic illness or total allergy syndrome) are expensive, they also lack scientific foundation in detecting adverse reactions to food, and should be avoided. A popular but unproven theory is that food and chemical sensitivity leads to the common somatic complaints of headache, fatigue, malaise, disorientation and dizziness, among others. Tests are being heavily promoted directly to the public, against the advice of the vast majority of medical opinion leaders and medical researchers. Included in these tests are the IgG test, Vega test or kinesiology test, the muscle weakness test, and the hair test.

How Can Food Allergy Be Prevented?

There are two main considerations in the prevention of food allergy.

  1. Pre-disposition to Allergy. It should be borne in mind that children with parents or siblings who suffer from allergies are more inclined to have allergies themselves.
  2. Breast-Feeding. Breast-feeding for a period of at least 6 months should be encouraged for all newborns. This is especially important if a child has an allergic pre-disposition. Recent research indicates that children should not avoid any potential allergenic foods, e.g., peanut, egg, etc., but that eating these foods decreases the risk of becoming allergic to these foods.

How Do I Know Whether I Am Eating Foods That May Cause Adverse Reactions?

Although many foods can cause adverse reactions these reactions are uncommon in the general populace and are limited to sensitised individuals. A number of foods commonly affect allergic individuals and these should be declared on the labels of food products:

Cereals containing gluten: e.g., wheat, rye, barley, oats, spelt or their hybridized strains, and products of these;

Crustacea and products of these: e.g., mussels, oysters, crayfish, prawns

Eggs and egg products;

Fish and fish products;

Peanuts, soybeans, and products of these;

Milk and milk products (including lactose);

Tree nuts and nut products: e.g., walnuts, pecans, almonds, cashews, macadamia nut, Brazil nuts, hazelnut;

Sulphite (sulphur dioxide) in concentrations of 10 mg/kg or more.

In certain countries, mustard, celery, buckwheat, lupine, sesame seed are prevalent allergens in those population groups, and these foods need to be listed on labels.

Where Can I Get More Information?

Updated for FACS by HSt (2016)