Tree nuts allergy
Information provided in co-operation with the Food-INFO.net website.

Allergies to tree nuts and seeds tend to be of a more severe nature, causing life-threatening and sometimes fatal reactions. People with tree nut allergies also often suffer from reactions triggered by a number of different types of nuts, even though they do not come from closely related plant species. In general these allergies are triggered by the major proteins found in nuts and seeds which are resist processes such as cooking.


 

There is also a milder form of tree nut allergy which is associated with birch pollen allergy, where symptoms are confined largely to the mouth, causing a condition called “oral allergy syndrome” (OAS). This condition is triggered by molecules found in tree nuts which are very similar to pollen allergens like the major birch pollen allergen called Bet v 1. These molecules tend to be destroyed by cooking, which can reduce the allergenicity of nuts and seeds for these allergic consumers.

Reactions to nuts and seeds can also occur as a consequence of hidden nut ingredients or traces of nuts and certain seeds introduced as a consequence of food handling or manufacturing. As a result tree nuts and seeds have been included in Annex IIIa of the EU food labelling directive. The following (including products thereof) must be declared on a label if they have been deliberately included in a food:

 

Table of nuts and foods containing nuts

Nuts (shelled fruit including peanuts)

Ingredients containing nuts (may not be allergenic)

Examples of prepared foods that may contain (traces of) nuts

Peanuts

Peanut oil

Bread and bakery products

Hazelnuts

Hazelnut oil

Pastry products (incl. pies)

Walnuts

Walnut oil

Cakes and cake mixes

Pecans

Coconut oil

Doughs (various)

Brazil nut

Almond oil

Chocolate and bonbons

Coconuts

Nut liquor

Salad Dressings

Almonds

 

Soups

Macadamia nuts

 

Egg based dumplings

Pine nuts

 

Sauces

Cashew nuts

 

Convenience foods

 

 

Crémes

 

 

Pudding

 

 

Flans

 

 

Icecream

 

 


 

  1.) Almond Allergy

Almond (Prunus dolcis, synonym: Amygdalus communis) is considered as a tree nut although almond belongs to the family of Rosaceae that also includes apple, pear, peach, cherry, plum, nectarine, apricot, and strawberry. Many processed foods may contain almond for example sweets, snacks, baked goods, ice cream, chewing gum, drinks (almond milk), curry.

 

 

 

Symptoms

Severity of almond-induced allergic reactions ranges from slight oral allergy syndrome (itching at the mouth and/or tongue soon after chewing and ingesting the fruit) to severe and even potentially fatal systemic reactions (anaphylactic shock; hives and swelling of the throat, asthma). Severity of allergic reactions depends on which protein(s) in the almond that the patient has become allergic to.

 

Who, when, how long, and how often?

Tree nuts are considered as one of the most frequent causes of food allergy, but almond allergy seems rather unusual. No good data for occurrence of almond allergy are available. In the United States and in the United Kingdom the frequency of tree nut allergy as a whole is estimated to range between 0.2% and 0.5% both in children and in adults. Tree nuts allergies appear early in childhood, but in Mediterranean countries sensitization to heat-resistant proteins may appear in adults. It is presently unknown whether allergic patients may become tolerant after some years of avoidance.

 

Related foods (cross reactivity)

Several types of almond-allergic subjects can be distinguished:

Patients with birch pollen allergy

In these patients almond allergy is the consequence of cross-reactivity (similarity) between pollen allergens and similar proteins in vegetable foods. As such proteins are rapidly destroyed in the stomach this kind of food allergy is generally mild: in most cases oral allergy syndrome is the only allergic symptom. Moreover, these patients tolerate heat-processed almonds because allergens are heat-labile.

Patients primarily allergic to tree nuts

Allergenic proteins responsible for this type of allergy are heat-stable and resistant to digestion in the stomach. As a consequence, patients reacting to these protein may experience severe allergic reactions. It is very important to be aware that severe reactions may occur on the first exposure to a nut in patients allergic to a different nut. Unfortunately, the cross-reactivity among tree nuts are very variable both in real life and when measured in blood samples. Thus, it is extremely important that patients with a history of severe allergic reactions to a tree nut avoid the ingestion of other nuts until the absence of reaction to almonds has been unequivocally demonstrated by properly performed diagnosis. Cross-reactivity between tree nuts and peanut is frequently observed on skin tests or in blood samples due to the presence of similar proteins, but actual clinical cross-reactivity is rare.

Patients allergic to peach and other Rosaceae

These patients react primarily to a heat-stable protein (LTP) present mainly in Rosaceae but also in most other plant-derived foods. LTP is a widely cross-reacting allergen. Most LTP-allergic subjects have a history of peach allergy (OAS and/or more severe reactions), and about 25% report reactions eating almonds. Allergy to other tree nuts is possible in these patients. LTP is heat-stable and resistant to digestion in the stomach; as a consequence allergic patients may potentially experience severe allergic reactions.

Patients allergic to latex

Some cases of almond allergy have been reported in patients allergic to natural rubber latex. However such association does not seem typical or frequent.

 

Diagnosis

Skin tests with fresh food are generally considered the best in-vivo method to detect walnut allergy, although commercial extracts may prove equally sensitive in patients sensitized to stable allergens. In vitro tests (RAST) are generally also sensitive. Due to the severity of allergic reactions induced by tree nuts oral challenge tests are rarely performed.

 

Avoidance

Almond may be present as a “hidden allergen” in commercial food preparations; a case of almond-induced anaphylaxis due to the ingestion of curry is described. Due to possible cross-reactivity, almond-allergic patients should avoid other tree nuts, such as hazelnut and Brazil nuts, unless their good tolerance has been clearly proven by reliable tests.

 

Further information

 


 2.) Hazelnut allergy

Hazelnuts (Corylus avellana) are among the common tree nuts that lead to allergic reactions. They can be eaten as in-shell nuts, however, the majority is cracked, and the kernels are sold to candy makers, bakers and other food processors. Hazelnuts can be found in many food products including cookies, cakes, pastries, chocolates, confectionary products, ice cream, breakfast cereals, and bread. In addition, hazelnut oil may pose a threat to patients with hazelnut allergy, depending on the method of processing with oil undergone less processing at lower temperature tended to be more allergenic.

 

 

Symptoms and cross reactivity

Allergy to hazelnut is often found in patients with hay fever (allergic rhinoconjunctivitis) and tree pollen allergy. These patients usually present with itching, swelling, burning in the mouth and throat after the ingestion of hazelnuts or hazelnut containing products. This so called “oral allergy syndrome” or food-pollen allergy is caused by cross-reactivity between tree pollen allergens, especially birch, alder and hazel pollen, and hazelnut proteins. In addition to the “oral allergy syndrome” severe allergic reactions to hazelnuts are reported in patients without any association to tree pollen allergy. These patients usually display hives (urticaria), swelling of the lips and face (angioedema), breezing difficulties (asthma or swelling of the throat), vomiting, diarrhoea and/or anaphylactic shock.

 

Dose

In one study using double blind, placebo-controlled food challenges, the lowest dose inducing symptoms in hazelnut allergic patients was 1 mg of hazelnut protein. After a dose between 30 to 100 mg of hazelnut protein, corresponding to one-third of a nut, all patients had developed an allergic reaction. Most patients in this study suffered from pollen-related food allergy. No data on sensitivity (threshold dosages) are reported so far for patients with severe allergic reactions to stable non-pollen-related hazelnut allergens. Minimum provoking doses could be different in this group and might be even lower. In general, the observed threshold levels equal doses of hidden hazelnut sometimes present in food products. Therefore a precise declaration is necessary to prevent unknown exposure. Methods have been developed appropriate for use in food industry that allow the detection of <10 parts-per-million (milligrams per kilogram) of hazelnut protein. However, globally the usage of such tests is no routine yet.

 

Who, when how long, and how often?

Hazelnut allergy is fairly common in Europe and the United States; however, not many studies of the occurrence exist. The frequency and the type of allergic reaction seem to vary considerably from one geographic region to another depending on the presence of birch, alder or hazel trees. The cross-reactivity between these tree pollen and nut allergens can be the leading cause of hazelnut allergy. In an epidemiological study of food allergy in adults performed in Germany the prevalence rate for nut allergy was shown to be 5%. Moreover, about 18% of the population studied was reacting to hazelnut when measured by skin prick test. A strong connection was observed for hazelnut-sensitized individuals, of whom 94% also reacted to birch pollen. In contrast, in a random digital telephone survey performed in 2002 in the United States the overall occurrence of isolated tree nut allergy was only 0.4% and for both, peanut and tree nut allergy, 0.2%. About 1/3 of these tree nut allergic subjects reported to have allergic reactions to hazelnuts. Allergic reactions to hazelnut can develop at any age; however, seem to depend again on the type of symptoms. The age of onset of “oral allergy syndrome” is beyond infancy but often before school age correlating to the time allergic hayfever develops. Systemic hazelnut allergy can develop already in infancy. A close relation to other food allergies, especially peanut allergy, is suggested. Peanut and tree nut allergies are infrequently outgrown and the foods may cause severe symptoms and even death.

 

Diagnosis

For most patients with suspected hazelnut allergy, currently used diagnostic tests, such as blood samples or skin prick tests give no clear-cut diagnosis. Only for highly reactive patients with high levels of nut-specific IgE or large skin test reactions it can be proposed that about 95% of these patients will have clinical reactions upon ingestion of the nut. Most results from allergy tests, however, will lie in a ‘grey area' beneath these values, but still positive where one could not be certain. These patients may be allergic or tolerant to the tested food. Moreover, variability in the composition of commercial skin prick test reagents for the diagnosis of hazelnut allergy is extreme. Sometimes, allergens important especially for severe systemic reactions to hazelnut are missing in the preparations. These shortcomings in standardization and quality control can potentially cause a false-negative diagnosis in subjects at risk of severe reactions to hazelnuts. Therefore, the gold standard is still the oral food challenge, best in a double-blind, placebo-controlled way. Recipes for hazelnut food challenges have been developed and validated.

 

Avoidance

Patients with diagnosed hazelnut allergy, especially those with systemic reactions, should completely avoid hazelnuts and hazelnut containing products. Currently, patients allergic to peanuts are advised to avoid also all tree nuts, including hazelnuts. Moreover, avoidance of all tree nuts is commonly recommended in patients allergic to any tree nut. Whether these recommendations are useful can be discussed. The elimination of all nuts is very difficult and has a great impact on the lifestyle. In addition, nuts are an important source of protein. It has recently been reported that 55% of patients allergic to one nut were able to tolerate another type of nut. Therefore the clinical relevance of hazelnut allergy should be proven before general avoidance is recommend especially since hazelnut are used in so many common food products. Moreover, infants in risk groups for developing allergy, such as infants with allergic parents or siblings, should avoid these foods in the first few years of life. The success of elimination diets depends on the recognition by the consumer of the offending food in food products. Hazelnut as a tree nut will be identifiable in food products through to the new EU labelling directive that is used since 2005.

It is well know that heating, cooking or roasting can change the ability of a food to elicit allergy. Processed food may be either more or less allergenic. It had been shown for hazelnuts that roasting seems to reduce the reactions at least for birch pollen allergic patients due to the fact that the responsible hazelnut-allergens are destroyed by heat. However, since about 30% of the patients with food-pollen allergy still showed allergic reaction to the roasted nuts, ingestion of roasted hazelnuts or products containing roasted nuts can not be considered safe for hazelnut allergic consumers. Moreover, the risk imposed by roasted hazelnuts to patients without tree pollen allergy but severe systemic reactions to hazelnuts is not known today. Hazelnut-allergens eliciting these systemic reactions belong to the same protein family as the allergens in peanuts. At least for the peanut allergens it is known that roasting increases the allergenicity of these proteins.

 

Further information:

 


3.) Walnut allergy

English walnut (Juglans regia) is a tree nut of the family Juglandaceae. To this family belong also other tree nuts including Pecan (Carya illinoiensis), black walnut (Juglans nigra and Juglans californica) and butternuts (Juglans cinerea). Many processed foods may contain walnut including sweets, snacks, baked goods, ice cream, soft cheeses.

 

Symptoms

Severity of walnut-induced allergic reactions ranges from slight oral allergy syndrome (itching in the mouth and/or tongue soon after chewing and ingesting a walnut) to severe and even potentially fatal systemic reactions (anaphylactic shock; hives and swelling of the throat, asthma). Severity of allergic reactions depends on which protein(s) in the walnut the patients have become allergic to.

 

 

Related foods (cross reactivity)

In general walnut-allergic subjects fall within the following categories:

Patients with birch pollen allergy that react to walnut (as well as to other fruits and vegetables):

In these patients walnut allergy is the consequence of cross-reactivity between pollen allergens and similar proteins in vegetable foods. This kind of food allergy is generally mild: in most cases oral allergy syndrome (OAS) is the only consequence of the ingestion of offending food. The absence of severe systemic symptoms is due to the fact that allergenic proteins are easily destroyed in the stomach. Moreover, they are heat-labile; as a consequence, patients tolerate heat-processed foods.

Patients primarily allergic to other tree nuts (including hazelnut, Brazil nut, macadamia nuts, etc):

Proteins responsible for this type of allergy are heat-stable and resistant to digestion in the stomach; thus, patients reacting to these proteins may experience severe allergic reactions. It is very important to be aware that severe reactions may occur on the first exposure to a nut in patients allergic to a different nut. From studies in which controlled challenges have been performed it has been calculated that walnut-allergic patients have a 37% risk of reacting to other tree nuts such as Brazil nut, cashew, and hazelnut. Unfortunately, the cross-reactivity among tree nuts are very variable both in real life and when measured in blood samples and sometimes involves unusual foods such as coconut. Thus, it is extremely important that patients with a history of severe allergic reactions to a tree nut avoid the ingestion of other nuts until the absence of reactions to walnut has been unequivocally demonstrated by properly performed diagnosis.

Cross-reactivity between tree nuts and peanut is frequently observed in skin prick tests or in blood samples due to the presence of similar proteins, but actual clinical cross-reactivity is very rare.

Patients allergic to peach (and/or other Rosaceae such as apple, pear, cherry, apricot, plum, or almond):

These patients are primarily reacting to a heat-stable protein named LTP (lipid transfer protein) present mainly in Rosaceae but also in most other plant-derived foods. Most patients have a history of peach allergy (OAS and/or more severe allergic reactions). About 50% of patients reacting to LTP react to walnut (as well as to other tree nuts) due to the cross-reactivity between LTP from botanically unrelated vegetable foods. Tree nuts (walnut, hazelnut) as well as peanut seem the most hazardous foods other than Rosaceae for LTP-hypersensitive patients. The likelihood of getting sensitized to vegetable foods other than Rosaceae is directly related to the level of IgE to peach LTP. LTP is heat-stable and resistant to digestion in the stomach; and as a consequence allergic patients may experience extremely severe reactions including anaphylaxis.

 

Who, when how long, and how often?

Tree nuts, particularly walnut, are one of the most frequent causes of food allergy.

Occurrence data are rather scarce for walnut allergy. In the United States and in the United Kingdom the prevalence of tree nut allergy is estimated to range between 0.2% and 0.5% both in children and in adults. Walnut allergy may appear early in childhood. The possibility exists that a percentage of patients with walnut allergy may become tolerant after some years of avoidance, but this is presently unknown.

 

Diagnosis

Skin tests with fresh food are generally considered the best way to detect walnut allergy, although commercial extracts may prove equally sensitive in patients sensitized to stable allergens. Blood samples are generally equally sensitive.

 

Avoidance

As opposed to other tree nuts (e.g. hazelnut) or from peanut, walnut is rarely present as a “hidden food” in commercial preparations. Therefore, inadvertent ingestion of walnut should be rare. However, walnut-allergic patients should carefully avoid other tree nuts, such as hazelnut and Brazil nuts, unless their good tolerance has been clearly proven by reliable tests. 

 

Further information:

 


This article was written in co-operation with the Food-Info.net website, an initiative of the Wageningen University, The Netherlands . We gratefully thank the authors behind the Food-Info website for providing us with the information for this article. For further information please visit http://www.food-info.net.