Is a peanut not a nut? Where did fistnuts come from
According to the botanical classification, peanuts – also known as groundnuts (or peanuts) – are not nuts, but legumes. They therefore belong to the same family as peas, soya beans and lentils. To this they owe their high protein content – much higher than in tree nuts (walnuts, hazelnuts, Brazil nuts, macadamia pine nuts, pecans, cashews) [1].
Peanuts are native to South America and their cultivation is favoured by subtropical and tropical climates. They were only recognised by Europeans during the expansion into the New World. Spanish and Portuguese colonisers came across indigenous peanut cultivators in Mexico, Peru, Brazil and other countries in the Rio de la Plata basin (Argentina, Paraguay, Bolivia). Fistas became widespread in Europe, Africa, Asia and the Pacific islands much later [2]. Their popularisation was mainly influenced by the Second World War. It was then that nutritious, high-protein peanuts were fed to soldiers.
Today, almost half of the world’s peanut production belongs to China. India and the USA are also significant producers [1].
Peanut allergy – Americans lead the way
The United States is most associated with peanuts. Peanuts are the raw materials used for the mass production of peanut butter, a treat that nearly 90% of Americans regularly reach for [3]. Peanut butter and jelly sandwiches are popular lunchbox snacks in the USA [4]. Therefore, this is the country with the highest recorded peanut allergy rate of almost 2% [1,5]. One in five people with a food allergy, or about 6 million people, reacts to fistachios. It is the leading food allergy among American children [6].
Peanuts are estimated to be responsible for 59% of anaphylaxis deaths in the US [1]. They are the leading cause of anaphylactic reactions – not only in the US, but worldwide [1].
Why is this type of allergy much more common in the USA than in China – despite the equally high consumption of peanuts? There is a hypothesis that the way peanuts are processed matters here. Peanut butter is made from nuts roasted dry (which increases its allergenicity). In contrast, the Chinese usually eat boiled or fried nuts [5,7]. Unlike other common food allergens (milk, egg), boiled peanuts are less allergenic than after higher temperature processing (roasting, baking) [1].
Fisticuffs full of allergens. When to expect anaphylaxis?
About 0.78%, or more than 28,000 Poles, have a peanut allergy [1]. This type of allergy has been shown to be increasingly common among children worldwide, especially in Western countries [1]. In the USA, Canada, the UK and Australia, its prevalence has tripled in the last 20 years [17]. Symptoms in an allergic person usually appear before the age of 14 years, often as early as early childhood (in 1.-2 years) [8]. It is usually a persistent allergy, i.e. one that one does not grow out of [1,9].
Approximately 10% of peanut proteins are substances of known allergenic nature. More than a dozen have already been identified.
PROTEIN FAMILY | MOLECULES |
| Spare proteins | 7S globulins: Ara h 1 11S globulins: Ara h 3 2S albumin: Ara h 2, Ara h 6, Ara h 7 |
| Profilins | Ara h 5 |
| PR-10 | Ara h 8 |
| nsLTP | Ara h 9, Ara h 16, Ara h 17 |
| Oleosins | Ara h 10, Ara h 11, Ara h 14, Ara h 15 |
| Defensins | Ara h 12, Ara h 13 |
The most relevant are Ara h 1, Ara h 2 (the main allergen) and Ara h 3 [9]. In Poland, Ara h 2 and Ara h 6 are the most common allergens [8].
Caution: anaphylaxis!
Sometimes just trace amounts of peanuts (a few milligrams) can be extremely dangerous. Even such a dose can cause an immediate allergic reaction, even fatal, although allergy symptoms are usually mild [1]. Of course, it all depends on what specifically sensitises us in the nuts. Allergy to spare proteins and defensins is associated with severe systemic reactions [10]. Studies show that 1 in 3 people with peanut allergy will experience anaphylaxis at least once in their lifetime [1].
Fisticuffs are found in many food products (especially sweets, confectionery, sauces), which increases the risk of accidental ingestion [1]. Contamination with these allergens often occurs during food processing and transport [1].
Anaphylactic reactions mostly occur outside the home. Therefore, peanut allergy is an indication to carry epinephrine (preferably two doses), available as an ampoule-syringe or auto-injector [4].
Ara h 2 or Ara h 3 – how do you know what’s allergenic? Diagnosis of peanut allergy
The diagnosis of allergy is based on a thorough medical history, which establishes a link between the characteristic symptoms and the consumption of peanuts. Diagnostic tests (both or one of two) are also necessary to establish the diagnosis:
- point skin tests (PTS) with standardised peanut extract,
- blood tests for the determination of serum antigen-specific IgE (sIgE) [15,16].
Molecular allergy tests are an extremely valuable adjunct to diagnosis – they are the ones that can pinpoint the correct allergenic particle and assess the risk of an anaphylactic reaction. With such tests, it is also possible to check whether symptoms are actually due to peanut allergy or whether they are the result of a cross-reaction [15,16].
In some cases, an oral provocation test is used (only under strict medical supervision) [15,16].
What are the symptoms of peanut allergy?
Diseases such as asthma, allergic rhinitis and atopic dermatitis (AD) often co-exist with peanut allergy [1], which may be associated with increased reactions after peanut ingestion. The following symptoms are grounds for suspecting allergy (after contact with peanuts by oral, percutaneous or inhalation routes):
- oral allergy syndrome (OAS) – itching, tingling of the lips and throat, swelling of the tongue,
- urticaria, redness and itching of the skin (local or generalised),
- swallowing disorders,
- cough, breathlessness, hoarseness and wheezing,
- watery nose,
- paroxysmal sneezing,
- watery eyes
- spasmodic abdominal pain,
- nausea, vomiting and diarrhoea,
- angioedema,
- bronchospasm,
- laryngeal oedema, airway obstruction,
- a drop in blood pressure [1,8,12].
In an anaphylactic reaction, symptoms originate from at least two systems (respiratory, gastrointestinal, cardiovascular, skin), occur rapidly and progress rapidly [13]. This reaction culminates in anaphylactic shock, which is usually associated with a significant drop in blood pressure, acute dyspnoea, loss of consciousness, convulsions, laryngeal closure due to oedema and inability to breathe [14].
Peanuts and cross-reactions
Peanut allergy symptoms may result from cross-reactivity. Ara h 8 reacts with the major allergen of birch pollen (Bet v 1) [9]. This means that people who are allergic to birch can have symptoms after ingesting fistas (especially during the pollen season of this tree). The profilin Ara h 5 (reacts with Bet v 2 of birch pollen and Phl p 12 of meadow thyme) is also involved in the pollen-food syndrome [9]. In addition, people with peanut allergy may also experience symptoms after eating other legumes: lentils, soya, beans, peas, fenugreek and lupin [11].
