tree nuts

In the NYT Science Times on 4/9/13: “Walnuts for Diabetes” by Nicholas Bakalar:

Eating walnuts may reduce the risk for Type 2 diabetes in women, a large new study concludes.

Previous studies have suggested an inverse relationship between tree nut consumption and diabetes. Though the findings are correlational, walnuts are uniquely high in omega-3 and omega-6 fatty acids, which may be of particular value in Type 2 diabetes prevention.

Tree nut turns out to be a culinary rather than botanical term, though its function is to distinguish (culinary) nuts that grow on trees — “true” (culinary) nuts — from peanuts, the fruits of which mature underground. This despite the fact that there’s a lot of allergy crossover between the two types, to the extent that many sites refer to “PN/TN allergies”, for ‘peanut/tree nut allergies’.

From Wikipedia on allergies:

Tree nut allergy, a hypersensitivity to dietary substances from tree nuts causing an overreaction of the immune system, may lead to severe physical symptoms. Tree nuts include almonds, Brazil nuts, cashews, chestnuts, filberts/hazelnuts, macadamia nuts, pecans, pine nuts (pignolia nuts), pistachios, and walnuts.

People with tree nut allergy are seldom allergic to just one type of nut, and are therefore usually advised to avoid all tree nuts, even though an individual may not be allergic to all varieties of tree nuts. Someone allergic to walnuts or pecans may not have an allergy to cashews or pistachios, even though close biological relatives often share related allergenic proteins. The severity of the allergy varies from person to person, and exposure can increase sensitization. For those with a milder form of the allergy, a reaction which makes the throat feel like cotton may occur. The raw nut protein usually causes a more severe reaction than the oil, and extra roasting or processing can reduce the allergic reaction. Those diagnosed with anaphylaxis will have a more immediate mast cell reaction and be required to avoid all exposure to any allergen-containing products or byproducts, regardless of processing, as they are prone to even greater sensitivity. An allergy test or food challenge may be performed at an allergy clinic to determine the exact allergens. New immunotherapy treatments are being developed for tree nut allergy.

Tree nut allergy is distinct from peanut allergy, as peanuts are considered legumes, whereas a tree nut is a hard-shelled fruit of certain plants.

To remind you of the terminological complexity here, let me take you back to nut as a botanical (technical) term. From my “stone fruits, nuts, and berries” posting:

A nut is a fruit composed of a hard shell and a seed, where the hard-shelled fruit does not open to release the seed (indehiscent). So, while, in a culinary context, a wide variety of dried seeds are often called nuts, in a botanical context, only ones that include the indehiscent fruit are considered true nuts [“true X” indicates a claim that the technical, botanical, classification and terminology is the only true one]. The translation of “nut” in certain languages frequently requires paraphrases as the [word] is ambiguous.

Most seeds come from fruits that naturally free themselves from the shell, unlike nuts [in the botanical sense] such as hazelnuts, chestnuts, and acorns, which have hard shell walls and originate from a compound ovary. Culinary usage of the term is less restrictive, and some nuts as defined in food preparation, like pistachios and Brazil nuts, are not nuts in a botanical sense. Common usage of the term often refers to any hard-walled, edible kernel as a nut.

The posting observes that (botanically) almonds are seeds rather than nuts. So are macadamias and pignolias (aka pine nuts), “the edible seeds of pines” (link). And cashews as well:

The cashew, Anacardium occidentale, is a tree in the family Anacardiaceae.

… The fruit of the cashew tree is an accessory fruit (sometimes called a pseudocarp or false fruit). What appears to be the fruit is an oval or pear-shaped structure, a hypocarpium, that develops from the pedicel and the receptacle of the cashew flower. Called the cashew apple, better known in Central America as “marañón”, it ripens into a yellow and/or red structure about 5–11 cm long. It is edible, and has a strong “sweet” smell and a sweet taste. The pulp of the cashew apple is very juicy, but the skin is fragile, making it unsuitable for transport. In Latin America, a fruit drink is made from the cashew apple pulp which has a very refreshing taste and tropical flavor that can be described as having notes of mango, raw green pepper, and just a little hint of grapefruit-like citrus.

The true fruit of the cashew tree is a kidney or boxing-glove shaped drupe that grows at the end of the cashew apple. The drupe develops first on the tree, and then the pedicel expands to become the cashew apple. Within the true fruit is a single seed, the cashew nut. Although a nut in the culinary sense, in the botanical sense the nut of the cashew is a seed. (link)

Of the 10 culinary tree nuts listed in the article on tree nut allergy, it turns out that only two. chestnuts and filberts/hazelnuts, are botanically nuts. (So are acorns, though these aren’t staples of the modern American diet.) Even walnuts, potentially useful in diabetes prevention, are botanically seeds rather than nuts.

3 Responses to “tree nuts”

  1. Tané Tachyon Says:

    I’m eating cashews right now while reading this.

  2. rjp Says:

    Apropos of nothing, brazil nuts are sexually transmittable. Kinda.

    http://scientopia.org/blogs/scicurious/2011/08/12/friday-weird-science-nutty-semen/

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