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. The translation of "nut" in certain languages frequently requires paraphrases as the concept is ambiguous.
Most seeds come from fruits that naturally free themselves from the shell, unlike nuts 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.
Botanical definition 
A nut in botany is a simple dry fruit with one seed (rarely two) in which the ovary wall becomes very hard (stony or woody) at maturity, and where the seed remains attached or fused with the ovary wall. Most nuts come from the pistils with inferior ovaries (see flower) and all are indehiscent (not opening at maturity). True nuts are produced, for example, by some plant families of the order Fagales.
- Order Fagales
- Family Juglandaceae
- Family Fagaceae
- Family Betulaceae
A small nut may be called a nutlet. Nutlet may refer to one of the following. In botany, this term specifically refers to a pyrena or pyrene, which is a seed covered by a stony layer, such as the kernel of a drupe. Walnuts and hickories (Juglandaceae) have fruits that are difficult to classify. They are considered to be nuts under some definitions, but are also referred to as drupaceous nuts. "Tryma" is a specialized term for hickory fruits.
Culinary definition and uses 
A nut in cuisine is a much less restrictive category than a nut in botany, as the term is applied to many seeds that are not botanically true nuts. Any large, oily kernels found within a shell and used in food are commonly called nuts.
Nuts are an important source of nutrients for both humans and wildlife. Because nuts generally have a high oil content, they are a highly prized food and energy source. A large number of seeds are edible by humans and used in cooking, eaten raw, sprouted, or roasted as a snack food, or pressed for oil that is used in cookery and cosmetics. Nuts (or seeds generally) are also a significant source of nutrition for wildlife. This is particularly true in temperate climates where animals such as jays and squirrels store acorns and other nuts during the autumn to keep from starving during the late autumn, all of winter, and early spring.
Some fruits and seeds that do not meet the botanical definition but are nuts in the culinary sense are:
- Almonds are the edible seeds of drupe fruits — the leathery "flesh" is removed at harvest.
- Brazil nut is the seed from a capsule.
- Candlenut (used for oil) is a seed.
- Cashew is the seed of an accessory fruit.
- Chilean hazelnut or Gevuina
- Macadamia is a creamy white kernel of a follicle type fruit.
- Malabar chestnut
- Peanut is a seed and from a legume type fruit (of the family Fabaceae).
- Pine nut is the seed of several species of pine (coniferous trees).
- Pistachio is the seed of a thin-shelled drupe.
Nutritional benefits 
Several epidemiological studies have revealed that people who consume nuts regularly are less likely to suffer from coronary heart disease (CHD). Nuts were first linked to protection against CHD in 1993. Since then many clinical trials have found that consumption of various nuts such as almonds and walnuts can lower serum LDL cholesterol concentrations. Although nuts contain various substances thought to possess cardioprotective effects, scientists believe that their Omega 3 fatty acid profile is at least in part responsible for the hypolipidemic response observed in clinical trials.
In addition to possessing cardioprotective effects, nuts generally have a very low glycemic index (GI). Consequently, dietitians frequently recommend nuts be included in diets prescribed for patients with insulin resistance problems such as diabetes mellitus type 2.
Nuts contain the essential fatty acids linoleic and linolenic acids, and the fats in nuts for the most part are unsaturated fats, including monounsaturated fats. Nuts also provide Arginine, a substance that may help make the walls of the arteries more flexible and less prone to blockage from blood clot formation.
Many nuts are good sources of vitamins E and B2, and are rich in protein, folate, fiber, and essential minerals such as magnesium, phosphorus, potassium, copper, and selenium.
Nuts are most healthy in their raw form. The reason is that up to 15% of the healthy oils that naturally occur in nuts are lost during the roasting process. Roasting at high temperatures could also cause chemicals that advance the aging process to form.
Raw or unroasted walnuts were found to have twice as many antioxidants as other nuts. Although initial studies suggested that antioxidants might promote health, later large clinical trials did not detect any benefit and suggested instead that excess supplementation of antioxidant supplements is harmful.
Other uses 
The nut of the horse-chestnut tree (Aesculus species, especially Aesculus hippocastanum), is called a conker in the British Isles. Conkers are inedible because they contain toxic glucoside aesculin. They are used in a popular children's game, known as conkers, where the nuts are threaded onto a strong cord and then each contestant attempts to break their opponent's conker by hitting it with their own. Horse chestnuts are also popular slingshot ammunition.
Historical usage 
Nuts, including the wild almond, prickly water lily, acorns, pistachio and water chestnut, were a major part of the human diet 780,000 years ago. Prehistoric humans developed an assortment of tools to crack open nuts during the Pleistocene period. Aesculus californica was eaten by the Native Americans of California during famines after the toxic constituents were leached out.
See also 
- List of culinary nuts
- List of edible seeds
- Nucifera (disambiguation), a Latin epithet for species bearing nuts
- Alasalvar, Cesarettin; Shahidi, Fereidoon. Tree Nuts: Composition, Phytochemicals, and Health Effects (Nutraceutical Science and Technology). CRC. p. 143. ISBN 978-0-8493-3735-2.
- Black, Michael H.; Halmer, Peter (2006). The encyclopedia of seeds: science, technology and uses. Wallingford, UK: CABI. p. 228. ISBN 978-0-85199-723-0.
- "Common Food Allergens". Food Allergy & Anaphylaxis Network. Retrieved 2007-06-24.
- Lina Sequeira. Certificate Biology 3. East African Publishers. pp. 130–. ISBN 978-9966-25-331-6. Retrieved 29 July 2010.
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- Sabaté J, Fraser GE, Burke K, Knutsen SF, Bennett H, Linsted KD (1993). "Effects of walnuts on serum lipid levels and blood pressure in normal men". Engl J Med 328 (9): 603–607. doi:10.1056/NEJM199303043280902.
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- David Mendosa (2002). "Revised International Table of Glycemic Index (GI) and Glycemic Load (GL) Values". Retrieved 2007-11-23.
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- "ABC News: The Places Where People Live Longest". Retrieved January 18, 2007.
- "Eating Nuts: A Healthy Way to Lower Cholesterol". CholesterolAdvice.net.
- Kris-Etherton PM, Yu-Poth S, Sabaté J, Ratcliffe HE, Zhao G, Etherton TD (1999). "Nuts and their bioactive constituents: effects on serum lipids and other factors that affect disease risk". Am J Clin Nutr 70 (3 Suppl): 504S–511S. PMID 10479223.
- "Walnuts are the healthiest nut, say scientists". BBC News. March 27, 2011. Retrieved March 28, 2011.
- Baillie, J.K.; Thompson, A.A.R.; Irving, J.B.; Bates, M.G.D.; Sutherland, A.I.; MacNee, W.; Maxwell, S.R.J.; Webb, D.J. (2009). "Oral antioxidant supplementation does not prevent acute mountain sickness: double blind, randomized placebo-controlled trial". QJM 102 (5)): 341–8. doi:10.1093/qjmed/hcp026. PMID 19273551.
- Bjelakovic G; Nikolova, D; Gluud, LL; Simonetti, RG; Gluud, C (2007). "Mortality in randomized trials of antioxidant supplements for primary and secondary prevention: systematic review and meta-analysis". JAMA 297 (8): 842–57. doi:10.1001/jama.297.8.842. PMID 17327526.
- "Remains of seven types of edible nuts and nutcrackers found at 780,000-year-old archaeological site". Scienceblog.com. February 2002. Retrieved 2010-09-13.
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