Nuts and Seeds

Nut-allergic people are often told that they can safely eat seeds and vice versa – but what actually is the difference? Cressida Boyd dons her botanical hat and attempts to elucidate…

What is a seed?

A seed is the reproductive core of a plant’s fruit – the means that plants use to reproduce themselves. Of all the plant parts that humans eat, seeds are the most important for human health, providing us with oils, starch, protein, minerals and vitamins. Seeds are tiny powerhouses of energy, concentrated to encourage new plant life.

A seed (also called a kernel) is a tiny embryonic plant – the end product of the process of reproduction in seed plants. A seed contains three parts: an embryo, a supply of nutrients and a seed coat. The embryo contains the roots and shoot. The seed nutrient store contains the energy the seed needs to grow, and the seed coat protects the seed from drying out or injury. This covering can be paper thin and fused to the seed coat, as in a cereal, or hard and thick, as in a coconut. Seeds, however, are enormously varied and, to further muddy the waters, the terms we use, in common parlance, to describe seeds and their component parts and their botanical classification have little in common.

Edible seeds

Edible seeds can be split into three categories:
Cereals or grains
The most important seed food, cereals are grass-like crops whose seeds are mostly ground to make flour. They include: maize, rice, sorghum, wheat, barley, millet, rye, oats, buckwheat, quinoa, teff, spelt, amaranth.

Legumes (pulses, peas, beans)
Legumes all come from the same family of flowering plants but there are many varieties. The fruits of these plants are mostly pods that split to scatter their seeds. Some of them you will know and eat: soybeans, peas, lentils, kidney beans, chickpeas, peanuts, broad beans, mung beans, urad beans, any green beans, black-eyed beans, guar, lupin, vanilla.

Nuts
A nut in common and culinary parlance is any large oily kernel found within a shell and used as a food. Botanically a nut is a dry hard fruit, almost always with a single seed which does not fuse with the ovary wall and which rarely opens at maturity, unlike a legume whose long seed pod twists apart to scatter the seeds inside.

‘Botanical’ nuts include chestnuts, beechnuts, acorns and hazelnuts.
Groups of seeds that we normally think of as nuts but which are not, botanically speaking, true nuts include:
Drupes The seed is contained in a shell which in turn is surrounded by a fleshy fruit. Drupes include coconuts, almonds, walnuts, pistachios and cashews.
Capsules The outer fruit of the capsule splits apart to release the seeds. Capsules include Brazil nuts and poppy seeds.

Nut / seed allergies
So where does this leave people who have been diagnosed as allergic to nuts or seeds? The common definition of a food allergy is an inappropriate response to a protein in a specific food. In the light of the definitions above, anyone who is allergic to wheat, peanuts, sesame seeds or to Brazil nuts is, in fact, seed allergic. However, such a broad definition is of very little help in everyday practical allergen management.

Wheat
Wheat is normally seen as a grain rather than a seed and it is its gluten content that is more usually blamed for creating ill health than the allergenic potential of its seeds. However, there are certainly those who will have a genuine allergic reaction to the proteins found in wheat.

Nuts / seeds
In ‘nut/seed allergy’ the usual classification is peanuts, tree nuts and seeds such as sesame seeds. But, as many allergic people will know, and as the botanical definitions make clear, this division is very inaccurate as those who react to Brazil nuts may not to walnuts (both ‘tree nuts’) while those who react to peanuts may also react to lupins but may not to chick peas, mung beans or lentils, all of which are also legumes.

Even within similar groups there is little allergic homogeneity. For example, within the ‘drupe’ classification, cashew nuts and almonds tend to precipitate reactions in a relatively large number of people whereas very few people are allergic to coconuts. If you suspect that you have a serious allergy you will normally be tested for peanuts and for some ‘tree nuts’– walnuts and cashews are the most common tree nuts to cause allergic reactions.

A reaction to one tree nut does not indicate that you will be allergic to all tree nuts (less than 20% of nut allergics react to all tree nuts). However, there is a strong cross-reactivity between nuts of the same family. For example, if you react to walnuts it is highly likely that you will react to pecans; if you react to cashews you will probably react to pistachios etc.

Even though there is no biological relationship between peanuts and tree nuts (beyond the fact that both are seeds) those who are allergic to one are frequently allergic to the other.

Allergy management
Because of the complexity of the subject, and because of the dramatic and potential fatal reactions that nut/seed proteins can cause, those with suspected nut/seed allergies are normally recommended to avoid them all. And although this is a sensible and practical way forward, especially for young children, it does seem unfortunate that so many people should thereby be denied one of nature’s most nutritious foods.

One can only hope that accurate allergen testing becomes more accessible so that specific allergen-containing nuts and seeds can be better identified – and that treatments such as peanut immunotherapy soon become available to nut/seed-allergy sufferers.

First published in 2009

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.

 

Back to top