Know your nuts! (And seeds, and drupes, and legumes …)

Alex Gazzola looks at the definitions, classifications and regulations which apply to some of the most important food allergens, and finds that in order to avoid confusion, both context and consistency are vital.

BBQ Is a pine nut really a nut? And is that maybe-nut a food allergen? And what about the coconut? Or the peanut? Or the pili nut – a little-known but increasingly popular nut from the Philippines which is now finding its way into our stores? And what do you need to look out for if you or your child has food allergies to several nuts, seeds or even legumes?

In order to begin to find our way through this quagmire of terminology, rules and potential risks, we first need to be clear on what we mean by the expressions we use.

What is a food allergen?

It very much depends on context – do we mean a food allergen in the medical sense, or a food allergen in the context of labelling regulation?

Any food, pretty much, can trigger a food allergy in a sensitised patient, and therefore could justifiably be described as being a food allergen from an immunological perspective. There are cases on record of IgE-mediated allergy to goji berry, aubergine, cabbage, pear and lettuce – all foods rarely associated with allergic disease.

But in common discourse, what we often mean by a food allergen is one of the declarable food allergens – the 14 foods or groups of foods which manufacturers of pre-packed, on-shelf products are required to declare and emphasise in their ingredients lists within the UK and EU, and which food service providers must make available to customers on request.

What are the 14 declarable food allergens and food allergen groups?

They are:

* celery / celeriac
* cereals containing gluten (all types – including all forms of oat, even certified gluten-free)
* crustaceans (all types)
* eggs (all types)
* fish (all types)
* lupin
* milk (all mammalian types)
* molluscs (all types)
* mustard
* tree nuts (some types only)
* peanut
* sesame seed
* soya
* sulphites / sulphur dioxide

It’s important to note two points here:

1. Peanut is a legume, which happens to grow in the ground, hence is not in any way or form a tree nut, and stands alone as one of the 14, independently of the tree nut group.

2. Of the declarable allergen groups, only tree nuts are not an exhaustive umbrella category, with eight named tree nuts included, but others excluded.

The eight are:

* almond
* hazelnut
* walnut
* brazil nut
* cashew
* pecan
* pistachio
* macadamia

Other nuts – whether or not they are botanical nuts or pseudo-nuts or so-called nuts – are therefore not on the list of declarable food allergens.

Cultural / culinary versus Botanical

This is where things get a little tricky … Let’s look at some definitions.

What is a seed?

Botanically, a seed is an embryonic plant protected inside an outer covering.

There are botanical seeds which are seeds also in a culinary or popular sense – these can be both declarable food allergens (sesame, mustard) and foods which are not declarable allergens (pumpkin, sunflower).

There are also botanical seeds which in a culinary or cultural sense may not be thought of as seeds – again, these include both declarable food allergens (grains containing gluten are all seeds) and foods which are not declarable food allergens (chickpea, pea).

Although most seeds can potentially be food allergens in a medical sense, whether or not a food is a seed is not a useful indicator as to whether it is a declarable food allergen: for that, you need to consult the list of 14.

What is a fruit?

We consider a fruit a sweet fleshy plant product in a culinary sense, but for a botanical definition, a fruit is the component of a plant which contains or constitutes the seed.

Many of the plants which produce the most common declarable food allergens produce fruits in which the seed is held, including peanuts, cereal grains, and tree nuts.

What is a tree nut?

A ‘tree nut’ is a nut which grows on a tree, but that still leaves us with the thorny issue of what is a nut?

Again, it depends on context.

The eight declarable tree nut allergens are all commonly considered ‘nuts’, but botanically, most do not fit the stricter definition ...

So, a botanical nut is a dry fruit composed of a seed within, but unattached to, a hard shell that does not split open to release it.

Hazelnut is the only declarable allergen within the tree nut group which is also a botanical nut in this strictest sense.

Non-declarable but genuine botanical nuts also include the chestnut and the acorn.

Declarable culinary tree nuts which are botanically not nuts include the Brazil nut (which is a seed within a capsule, not a shell), and the walnut, pecan and almond, which are seeds of what is called a drupe, where the seed is found in a shell that is encased within an outer fleshy (or sometimes leathery or fibrous) layer.

Other drupes include coconut and apricot / apricot kernels, neither of which is either a botanical nut or a declarable food allergen.

And what is a legume?

Legumes grow in pods – if you’re shelling peanuts, that pod is dried, pale and shrivelled, but if you’re shelling peas, it’s fresh and green.

Legumes can be both declarable food allergens (peanut, lupin, soya) and foods which are not declarable food allergens too (broad bean, chickpea, lentil).

So why is a declarable allergen a declarable allergen?

Ultimately, the important thing to remember is that no declarable allergen was deemed to be so on the basis of its common name, nor of being a botanical or culinary seed or nut or legume or drupe – or not!

Each allergen was chosen due to it being considered a major allergen across European states, therefore among the greatest risks to its food-allergic residents.

The grouping together of the so-called tree nuts under one ‘tree nut’ category was one of pure practical convenience.

It is possibly due to a linguistic quirk that we have these endless debates over whether something is or isn’t a nut. Continental Europeans aren’t similarly cursed – they call their nuts ‘shell fruits’ or suchlike, as in Spain (frutos de cascara) France (fruits a coque) and Germany (schalenfruchte) – and so there is less discrepancy between botanical and cultural terms, and one imagines far less confusion.

In the UK, there is nothing else for it – if you wish to know whether a food is a declarable food allergen, you must simply consult the official list. Period.

The consequences …

For ingredient labelling

Declarable allergens must be named and emphasised in lists of ingredients, but bear in mind that all ingredients must be listed, so if you are allergic to a nut or so-called nut outside the 8 declarable ones, or indeed any other food not on the list of 14, you would normally find mention of them.

The problem arises when derivatives of these foods are used. Manufacturers in this instance are not obliged to declare the source.

As an example, vegetable protein derived from a ‘top 14’ allergen must be declared – for instance as “vegetable protein (from soya)” – vegetable protein derived from a non-top 14, such as corn, may not make that declaration.

If you are allergic to a food outside the top 14, you need to check these sources of potential ‘hidden’ allergen, and perhaps call manufacturers to find out more if there’s an ingredient whose source you cannot identify.

You can read more about this in my Foods Matter article, Rare Food Allergies.

For ‘free from’ labelling

‘Nut free’ need not necessarily mean free from nuts – be they botanical or culinary – other than the 8 named tree nuts and peanuts.

Be warned then that a ‘nut free’ labelled product could contain coconut, pine nut and chestnut, among others.

For ‘may contain’ labelling

Brands which use precautionary allergen labelling (the vast majority) will only warn you when there is a risk of cross-contamination from one or more of the top 14 allergens.

Cross-contamination from pine nuts or peas, for instance, is unlikely to be declared. It may well be worth checking with manufacturers in certain circumstances.

NB. The common PAL expression ‘may contain nuts’ can be interpreted as incorporating both the tree nuts and peanuts, according to the Food Standards Agency.

For cross reactions …

Cross reactions in food allergy – where a confirmed allergy to one food may result in a similar reaction to a closely botanically related other food – are common, but impossible to predict.

While there are known potential cross-reactive allergens in the legumes – ie between peanut and lupin, for example – in practice it depends on the individual, and advice should come from your allergy consultant if you are worried. Skin prick tests may not be helpful: around half of people with peanut allergy will have positive SPT to another legume, but the vast majority will tolerate that legume in the diet.

If you have peanut allergy, it is likelier you will have to avoid one or more tree nuts than you will one or more legumes. This may not be a cross-reactivity, but a simple co-existing allergy.

The various culinary tree nuts aren’t necessarily closely related to one another, although there are some connections – cashew and pistachio are both members of the larger cashew family, for instance, and pecans and walnuts are related too.

The various culinary seeds we use are generally not related at all – eg poppy, sesame and pumpkin are all from completely different plant sources – but, as with all foods, even non-related foodstuffs can potentially contain similar allergens to one another through simple coincidence of nature.

There is rarely a need to begin avoiding a food to which you do not react merely because it is botanically related to a food to which you do react.

And finally, to American friends, and travellers …

As far as the legislation discussed above goes, it applies only in the EU; laws vary elsewhere in the world.

In the US, tree nuts constitute one of their eight declarable allergens and allergen groups, but unlike in the EU, the group does incorporate coconut, ginkgo, pili, shea, argan and other nuts or so-called nuts, including pine nut, as well as the EU-defined tree nuts.

For more on the key differences between British and American food labelling from an allergy and coeliac perspective, see my Foods Matter article US vs EU Labelling, and for more on the implications of this for food allergy travellers from and to both territories, see Allergens: the big 8, the big 14, on my blog Allergy Insight.

November 2019

If you found this article interesting, you will find many more articles on peanut and tree-nut allergy here, and reports of research into the conditions here.
You can also find articles on anaphylaxis here, cow's milk allergies here, egg allergy here, histamine intolerance here and articles on a wide range of other allergic and intolerance reactions to a wide range of other foods here.

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