Nut

Hazelnuts from the Common Hazel

Chestnut

Botanically, a nut is a hard, indehiscent (not opening to discharge seeds), simple, dry fruit, whereby the plant's ovary wall becomes very hard (stony or woody) at maturity, and where the seed (usually single, rarely two) remains unattached or unfused with the ovary wall. Examples of such true nuts include acorns, chestnuts,hazelnuts, and pecans. However, the term also is used in less restrictive culinary terms to refer to any fruit with a hard outer covering or an edible seed that is surrounded by a hard shell. For example, a brazil nut is really a seed, the peanut is really a legume, and the almond and cashew are really seeds enclosed in a drupe.

Botanical definitions

A fruit, in a botanical sense, is the ripened ovary—together with seeds—of a flowering plant. In flowering plants, an ovary is the part of the carpel that holds the ovule(s); after pollination, the ovary will grow into the fruit, while the ovule(s) become the seed(s). In many species, the fruit incorporates the ripened ovary and surrounding tissues.

In other words, after an ovule is fertilized, the ovary begins to expand. The petals of the flower fall off and the ovule develops into a seed. The ovary eventually comes to form, along with other parts of the flower in many cases, a structure surrounding the seed or seeds that is the fruit. Fruit development continues until the seeds have matured. The wall of the fruit, developed from the ovary wall of the flower, is called the pericarp, which is often differentiated into two or three distinct layers called the exocarp (outer layer—also called epicarp), mesocarp (middle layer), and endocarp (inner layer).

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 unattached or unfused with the ovary wall. Most nuts come from pistils with inferior ovaries and all are indehiscent (not opening at maturity).

In summary, seeds are ripened ovules; fruits are the ripened ovularies or carpels that contain the seeds; and nuts are types of fruit and not another term for seeds.

True nuts are produced, for example, by some plants—families of the order Fagales.

Order Fagales

• Family Juglandaceae
  • Walnut—esp. Persian Walnut (Juglans regia)
  • Butternut (Juglans)
  • Hickory, Pecan (Carya)
  • Wingnut (Pterocarya)
• Family Fagaceae
  • Chestnut (Castanea)
  • Beech (Fagus)
  • Oak (Quercus)
  • Stone-oak, Tanoak (Lithocarpus)
• Family Betulaceae
  • Alder (Alnus)
  • Birch (Betula)
  • Hazel, Filbert (Corylus)
  • Hornbeam

Culinary definition and uses

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

A woman selling nuts at a roadside in Izmir Province, Turkey.

A nut in cuisine is a much less restrictive category than a nut in botany, as the term is applied (or misapplied, depending upon the viewpoint) to many seeds that are not 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 winter and early spring.

Nuts, including both tree nuts and peanuts, are among the most common food allergens.

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

• Almond is the edible seed of a drupe—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.
• Coconut is a dry, fibrous drupe.
• Horse-chestnut is an inedible capsule.
• Macadamia nut is a creamy white kernel (Macadamia integrifolia).
• Mongongo
• Peanut is a legume and a seed.
• Pine nut is the seed of several species of pine (coniferous trees).
• Pistachio nut is the seed of a thin-shelled drupe.

See also: List of edible seeds

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. Recent 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 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.

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

Other uses

The "nut" of the horse-chestnut (Aesculus hippocastanum), is also known as a conker. Conkers are inedible, due to the presence of the toxic glucoside aesculin, but are collected and used in an old children's game, also known as conkers, in which a nut is threaded onto a strong cord and then each child attempts to break their opponent's conker by hitting it with their own. A related species, Aesculus californica, was formerly eaten by the Native Americans of California in times of famine. It must be leached to remove the toxic constituents before eating.

References

ISBN links support NWE through referral fees

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

External links

All links retrieved October 27, 2007.

Wikimedia Commons has media related to:

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• Micronutrient Information Center - Linus Pauling Institute
• Nuts and their bioactive constituents: effects on serum lipids and other factors that affect disease risk - American Journal of Clinical Nutrition

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