A nut allergy in the stricter sense is an allergy to tree nuts. These include hazelnuts, walnuts, macadamia nuts and chestnuts. However, nut-like seeds and pits from stone fruits and capsules also have the potential to trigger nut allergies. Some examples are pistachios, pecans, almonds, cashews, Brazil nuts and pine nuts. In food shops, edible nuts and seeds are often sold together in the same category.
The prevalence of specific nut allergies varies widely according to region. In Europe, most people with tree nut allergies are allergic to hazelnuts, while in the U.S., walnuts and cashews are the tree nuts that most frequently trigger allergic reactions. At the global level, almonds, Brazil nuts, cashews, hazelnuts, macadamia nuts, pecans, pistachios and walnuts cause the most allergic reactions.
Scientific studies have demonstrated that around 1.4% of the European population is allergic to nuts. However, there are studies that contradict these findings in which the participants were not evaluated according to medical criteria but were instead asked questions about their allergy. According to self-reports, up to 11.7% of the European population is allergic to nuts.
Given that there are many kinds of nuts to which people can have an allergic reaction, there are also many different nut allergens. Each nut type has its own characteristic protein.
In primary food allergies, the patient experiences an immediate allergic reaction to certain proteins (protein compounds) in the nut, usually storage proteins. These proteins are important for the growth of the plant and are so stable that they cannot be altered by heat or stomach acid. Primary food allergies appear most frequently in childhood.
The allergy-triggering proteins of one type of nut are often similar to the protein structures of other nuts. If the immune system of a person who is allergic to certain nut proteins comes into contact with other nut proteins, an immune reaction may be triggered by these nuts as well due to the similarity.
Nuts or traces of nuts can be found in a wide range of food products. These include bread, bread rolls, cakes, tarts, ice cream, cookies, crackers, salty snacks, baking mixes, muesli, cereal bars, spreads and sweets, and also ready meals such as potato mash, potato croquettes, cheese dishes, prepared mince in the form of burgers patties, and breaded fish.
In some people, even the slightest trace of a nut allergen can trigger allergy symptoms.
In accordance with European food regulations, all foods containing nuts such as almonds, hazelnuts or walnuts must be labelled as such. This information must also be provided for non-packaged foods. Products that do not contain nuts can still have traces of nuts if they are processed in the same production facility. It is not always possible to tell whether this is the case because the warning ‘may contain traces of nuts’ is not mandatory for the manufacturer. Individuals with a severe allergy can ensure greater safety by contacting manufacturers directly.
Nut allergy symptoms usually appear within a few minutes of consumption. In some individuals, skin contact with the allergen is enough to trigger an allergic reaction. Symptoms can affect the breathing, skin and mucous membranes, eyes, digestive tract or the cardiovascular system and, in the most severe case, trigger an anaphylactic reaction. Nut allergy symptoms are similar to those of a peanut allergy.
Nut Allergy in Children and Adults
Nut allergies can occur in both children and adults. Unlike other food allergies, such as milk or chicken egg allergies, nut allergies almost never go away by themselves. Therefore children with nut allergies nearly always retain their allergies into adulthood.
Nut allergies that do not appear until adulthood are usually secondary allergies. In this case, the individual usually suffers originally from a birch pollen allergy. Since certain proteins in birch pollen are similar in structure to certain nut proteins, a cross-reaction can lead to a nut allergy. Secondary allergies are usually milder, with reactions limited to the mouth and throat.
If an allergy is suspected, the doctor asks the patient about his or her eating habits and symptoms, and analyses them to see if there are any correlations (anamnesis or patient history). For food allergies, positive blood tests or skin prick tests can help identify the trigger. However, it is important to keep in mind that allergy tests can predict the risk of an allergy but not the severity of any potential reactions.
Sometimes the patient history and laboratory tests are not enough to rule out all doubts. In this case, the most reliable method for determining whether an individual is allergic to a specific nut is to perform an oral provocation test. Because of the risk of a severe reaction during this test, it may only be conducted under strict medical supervision. A hospital stay is often required for this test.
As always, the recommended treatment for people with nut allergies is abstention, or allergen avoidance. It sounds easy, but it can be very difficult in everyday life. Particularly for vegetarians, vegans or people who follow a special diet for religious reasons, nuts and seeds are an important source of protein. This is why any changes in the diet must be supervised by a qualified nutritionist and should not be undertaken without a medical diagnosis.
For people at risk of a severe allergic reaction, it is important to educate patients and the parents and caregivers of allergic children about high-risk situations so that they are able to recognise the symptoms in time. People with nut allergies should not only avoid foods that contain nuts as ingredients, but also need to be careful with packaged foods that may be contaminated by nuts and/or traces of nuts.
People at risk of anaphylactic shock should always carry an emergency kit with them containing an adrenaline auto-injector, cortisone (in liquid or tablet form) and an antihistamine (in liquid or tablet form). As soon as symptoms appear, the dosage recommended by the doctor should be given to the patient immediately.
While preliminary experimental studies indicate that oral immunotherapy for hyposensitisation may be effectively used to treat peanut allergies in the future, there is currently no evidence that it can be used for tree nut allergies.
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