Allergy to almonds, or who and how may be harmed by marzipan

Tree nuts and drupe seeds are recognised as essential elements of a healthy, balanced diet. Among other things, they are rich in phytosterols, which lower blood cholesterol levels. Including nuts in the diet can help, for example, to reduce the risk of cardiovascular disease [3,4]. Almonds are the seeds of a drupe – the almond tree (Prunus dulcis) [5,6] – which is included in the broad group of tree nuts. The almond tree belongs to the same family (Rosaceae) as the pistachio tree.

Almonds are a very good source of plant protein, calcium and dietary fibre. Among nuts, they lead the way as a source of tryptophan, which is essential for the production of one of the most important neurotransmitters, serotonin. They also contain the most vitamin B2 (riboflavin) and vitamin B9 (folate) [4].
Unfortunately, nuts – and therefore almonds – are among the main sources of food allergens. They have been included in the so-called ‘big eight’, i.e. products that are responsible for about 90% of allergic reactions to food [2]. Nut allergy is the leading cause of fatal anaphylactic reactions (peanuts are responsible for about 20% of all anaphylaxis) [6,7].

The US Food Allergy and Anaphylaxis Network (FAAN) reported that people who react to almonds account for 15% of all tree nut-sensitive allergy sufferers (in the US) [3]. Within this group, those with allergies to walnuts (34%) and cashew nuts (20%) are most numerous. It is important to note that tree nuts do not include peanuts (groundnuts).

From an epidemiological point of view, almond allergy ranks fourth in terms of prevalence among nut allergies (of any type) [1]. However, it has not been comprehensively reported in the scientific literature [1,9].

An allergy to almonds can involve a range of reactions from mild to severe. These include:

• oral allergy syndrome (OAS), or pollen-food syndrome (e.g. birch-apple-nut syndrome in people allergic to birch pollen) [1,8]. OAS usually manifests with mild oral symptoms (itching, swelling of the lips and tongue). In rare cases, however, it can lead to anaphylaxis [8],
• allergic rhinitis,
•  gastrointestinal complaints,
• atopic dermatitis [1].

Allergy to nuts, including almonds, most often begins in childhood and, unlike other food allergies, rarely disappears. It is persistent and sometimes severe and life-threatening [1].

Almonds are usually eaten raw or roasted. They are often found in the ingredients of food products, especially cakes, pralines and other sweet snacks, liqueurs, but also baked goods, such as Indian naan bread [11]. They are the main ingredient in marzipan and some vegan and gluten-free products (almond milk, almond flour). They are classified as so-called “latent allergens” (e.g. candies with and without almonds are produced using the same machinery) [3,10].

Almond extracts and oils can also be found in cosmetic products such as creams, soaps, shampoos, hair conditioners and massage oils [11].

Allergenic proteins in almonds include:

• Pru du 1,
• Pru du 2,
•  Pru du 3,
• Pru du 4,
• Pru du 5,
• Pru du 6,
• Pru du 8,
• Pru du 10 [1,3].

Some of these proteins can cross-react. For example, with proteins found in walnuts, hazelnuts, sunflower seeds, peanuts, peaches, cherries, cherries, apples [1,3].

The allergen Pru du 2 belongs to the same group of proteins as the chief peanut allergen, Ara h 2. Pru du 3 (LTP), on the other hand, has a very similar sequence (94%) to apricot LTP (Prup 3) [3]. It is the protein most predisposed to exhibit cross-reactivity [1].

Pru du 5 is considered the main allergen of almonds – due to the presence of specific IgE antibodies in 50% of sensitised individuals [1]. However, the best studied allergen to date is Pru du 6, associated with the occurrence of severe allergic reactions. It shows high resistance to heat treatment [1].

Cross-reacting almonds can therefore unexpectedly cause allergic symptoms in people allergic to other nuts. Reactivity to many tree nuts affects up to a third of allergy sufferers (37%) [6]. Therefore, when a patient is diagnosed with an allergy to a particular nut, it is often recommended to avoid consumption of the entire group [1].

Also relevant to the risks of consuming almonds is the fact that they come in two varieties: sweet and bitter. These varieties are externally similar, but differ in their chemical composition.

Bitter almonds – unlike sweet almonds (the only ones that are edible raw) – contain a lot of amigdalin, which is broken down in the body to the poisonous hydrogen cyanide [3,4]. Hydrogen cyanide can even lead to death in an adult. However, by soaking almonds for several hours in warm water – as well as roasting them – the content of this substance is significantly reduced [4].

Aleksandra Lipiec

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tłumaczenie: Julia Majsiak