FOOD ALLERGIES AND INTOLERANCES
When people react to food, up to 35% assume they are suffering from a food allergy, though when they undergo a food challenge, the ‘gold standard’ of food allergy diagnosis, only up to 11% are in fact allergic. A hypersensitivity to food does not always mean an allergic reaction is taking place. A food hypersensitivity may present different types of reactions driven by different mechanisms in the body, as shown in the figure below:
To differentiate between a food allergy and a food intolerance, a certain procedure must be carried out which includes a detailed clinical history and, according to each case, specific diagnostic tests (e.g. H2-breath test, prick test, blood test for specific IgE antibodies, oral food challenge, elimination diet).
Food allergies during infancy usually occur with basic foods such as milk, eggs, nuts and wheat. Allergic adolescents and adults react to pollen-associated or latex-associated foods such as fruit, vegetables and nuts; this is known as “cross-reactivity”. With cross-reactions, related protein structures of different origin cannot be distinguished by the immune system, causing a reaction to both proteins. Examples include the reaction to apples when allergic to birch pollen or the reaction to kiwi when allergic to latex. Such reactions can range from mild tingling or itchiness in the oral cavity up to life-threatening anaphylactic reactions.
When an allergy is suspected to be the cause of a food hypersensitivity, it may under certain circumstances be necessary to carry out open food challenges or double-blind placebo-controlled food challenges (DBPCFC), when the suspected trigger foods have been narrowed down. The type of challenge to be performed depends on the clinical history and the age of the patient. In the case of a DBPCFC, the nutritionist prepares a test meal which contains the suspected food allergen and a test meal which does not contain the suspected food allergen (placebo). The performance of the food challenge must be supervised by a physician with expertise in food allergy diagnosis for up to several hours after each test meal has been administered. With DBPCFC, neither the physician, nor the patient know which test meal contains the food allergen and which the placebo, as these are masked in a food matrix. This not only lowers the chances of a false-positive reaction by the patient but also allows for an objective observation by the physician, lowering the possibilities of a false positive diagnosis.
Several other methods for the diagnosis of food hypersensitivity are also performed, though these remain unproven diagnostic tools according to international guidelines (EAACI, AAAAI). Such methods, even if they coincidently identify the trigger food causing an allergy or intolerance, often lead to unnecessary restriction of additional foods. Such extensive restrictions should therefore be avoided as this narrows down the food choices of the individual and significantly affects quality of life.
Food-specific IgG antibodies: as supported by the German S1-guidelines, the American Academy of Asthma, Allergy & Immunology as well as the European Academy of Allergy and Clinical Immunology, “food-specific IgG4 does not indicate (imminent) food allergy or intolerance, but rather a physiological response of the immune system after exposition to food components. Therefore, testing of IgG4 (or IgG) to foods is considered as irrelevant for the laboratory work-up of food allergy or intolerance and should not be performed in case of food-related complaints”.