Nut (fruit)

Hazelnuts from the Common Hazel

Chestnuts

A walnut and a walnut core having been removed from the outer pithy fruit. Walnuts are not true nuts.

A nut cracker used to cut hard nuts. Picture from Shimla Museum in Himachal Pradesh, India.

A nut is a hard-shelled fruit of some plants having an indehiscent seed. While a wide variety of dried seeds and fruits are called nuts in English, only a certain number of them are considered by biologists to be true nuts. Nuts are an important source of nutrients for both humans and wildlife.

Nuts are a composite of the seed and the fruit, where the fruit does not open to release the seed. Most seeds come from fruits, and the seeds are free of the fruit, unlike nuts such as hazelnuts, hickories, chestnuts and acorns, which have a stony fruit wall 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,^[1] are not nuts in a biological sense. Everyday common usage of the term often refers to any hard-walled, edible kernel as a nut.^[2]

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 Fagaceae
  • Beech (Fagus)
  • Chestnut (Castanea)
  • Oak (Quercus)
  • Stone-oak, Tanoak (Lithocarpus)
• Family Betulaceae
  • Alder (Alnus)
  • Hazel, Filbert (Corylus)
  • Hornbeam

Culinary definition and uses

Korean Pine nuts — unshelled, and shell, above; shelled, below

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 kernel found within a shell and used in food may be regarded as a nut.

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 them from starving during the late autumn, all of winter, and early spring.

Nuts used for food, whether true nut or not, are among the most common food allergens.^[3]

Some fruits and seeds that do not meet the botanical definition but are nuts in the culinary sense:

• Almonds, pecans and walnuts 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 nut is a seed.^[4]
• Gevuinanut
• Horse-chestnut is an inedible capsule.
• Macadamia nut is a creamy white kernel (Macadamia integrifolia).
• Malabar chestnut
• Corn nut is a cooked kernel
• Mongongo
• Peanut is a legume.
• Pine nut is the seed of several species of pine (coniferous trees).
• Pistachio nut is the seed of a thin-shelled drupe.

Nutritional benefits

A graph detailing the nutritional properties of nuts and oily seeds.

Several epidemiological studies have revealed that people who consume nuts regularly are less likely to suffer from coronary heart disease (CHD).^[5] Nuts were first linked to protection against CHD in 1993.^[6] 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.^[7]

In addition to possessing cardioprotective effects, nuts generally have a very low glycemic index (GI).^[8] Consequently, dietitians frequently recommend nuts be included in diets prescribed for patients with insulin resistance problems such as diabetes mellitus type 2.^[9]

One study found that people who eat nuts live two to three years longer than those who do not.^[10] However, this may be because people who eat nuts tend to eat less junk food.^[11]

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.

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.^[12]

Nuts are most healthy in their raw form.^[13] 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.^{[citation needed]}

Raw or unroasted walnuts were found to have twice as many antioxidants as other nuts.^[13] However, antioxidants are proving to be a tough nut to crack. Although initial studies suggested that antioxidants might promote health, later large clinical trials did not detect any benefit and suggested instead that excess supplementation is harmful. ^[14][15]

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 were a major part of the human diet 780,000 years ago including the wild almond, prickly water lily, acorns, pistachio and water chestnut. Prehistoric humans developed an assortment of tools to crack open nuts during the pleistocene period.^[16] Aesculus californica, was eaten by the Native Americans of California during famines after the toxic constituents were leached out.

See also

Food portal

• List of edible seeds

References

1. ^ Alasalvar, Cesarettin; Shahidi, Fereidoon. Tree Nuts: Composition, Phytochemicals, and Health Effects (Nutraceutical Science and Technology). CRC. p. 143. ISBN 978-0-8493-3735-2. 
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. 
3. ^ "Common Food Allergens". Food Allergy & Anaphylaxis Network. http://www.foodallergy.org/allergens/index.html. Retrieved 2007-06-24. 
4. ^ Lina Sequeira. Certificate Biology 3. East African Publishers. pp. 130–. ISBN 9789966253316. http://books.google.com/books?id=7AfHwKm8vu0C&pg=PA130. Retrieved 29 July 2010. 
5. ^ Kelly JH, Sabaté J (2006) Nuts and coronary heart disease: an epidemiological perspective. Br J Nutr 96, S61-S67.
6. ^ 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. N Engl J Med 328, 603-607.
7. ^ Rajaram S, Hasso Haddad E, Mejia A, Sabaté J (2009) Walnuts and fatty fish influence different serum lipid fractions in normal to mildly hyperlipidemic individuals: a randomized controlled study. Am J Clin Nutr 2009, 89, 1657S-1663S.
8. ^ David Mendosa (2002). "Revised International Table of Glycemic Index (GI) and Glycemic Load (GL) Values". http://www.mendosa.com/gilists.htm. Retrieved 2007-11-23. 
9. ^ Josse AR, Kendall CWC, Augustin LSA, Ellis PR, Jenkins DJA (2007) Almonds and postprandial glycemia — a dose response study. Metabolism, 56, 400-404.
10. ^ Fraser GE, Shavlik DJ (2001) Ten years of life: Is it a matter of choice? Arch Int Med, 161, 1645-1652.
11. ^ "ABC News: The Places Where People Live Longest". URL accessed January 18, 2007.
12. ^ 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, 504S-511S.
13. ^ ^{a b} "Walnuts are the healthiest nut, say scientists". BBC News. March 27, 2011. http://www.bbc.co.uk/news/health-12865291. Retrieved March 28, 2011. 
14. ^ 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.
15. ^ 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.
16. ^ "Remains of seven types of edible nuts and nutcrackers found at 780,000-year-old archaeological site". Scienceblog.com. http://scienceblog.com/community/older/2002/F/20022752.html. Retrieved 2010-09-13. 

• John Harvey Kellogg, "Nuts May Save the Race." The Itinerary of Breakfast. New York: Funk & Wagnalls Company, 1920. 165–203.

External links

• Linus Pauling Micronutrient Information Centre Nuts
• American Journal of Clinical Nutrition Nuts and their bioactive constituents: effects on serum lipids and other factors that affect disease risk
• Fruit and Nut Trees
• Nut research