A nut is a
fruit
In botany, a fruit is the seed-bearing structure in flowering plants that is formed from the ovary after flowering.
Fruits are the means by which flowering plants (also known as angiosperms) disseminate their seeds. Edible fruits in partic ...
consisting of a hard or tough
nutshell protecting a kernel which is usually edible. In general usage and in a culinary sense, a wide variety of dry
seed
A seed is an embryonic plant enclosed in a protective outer covering, along with a food reserve. The formation of the seed is a part of the process of reproduction in seed plants, the spermatophytes, including the gymnosperm and angiosper ...
s are called nuts, but in a botanical context "nut" implies that the shell does not open to release the seed (
indehiscent).
Most seeds come from fruits that naturally free themselves from the shell, but this is not the case in nuts such as
hazelnut
The hazelnut is the fruit of the hazel tree and therefore includes any of the nuts deriving from species of the genus '' Corylus'', especially the nuts of the species ''Corylus avellana''. They are also known as cobnuts or filberts according ...
s,
chestnut
The chestnuts are the deciduous trees and shrubs in the genus ''Castanea'', in the beech family Fagaceae. They are native to temperate regions of the Northern Hemisphere.
The name also refers to the edible nuts they produce.
The unrel ...
s, and
acorn
The acorn, or oaknut, is the nut of the oaks and their close relatives (genera '' Quercus'' and '' Lithocarpus'', in the family Fagaceae). It usually contains one seed (occasionally
two seeds), enclosed in a tough, leathery shell, and b ...
s, which have hard shell walls and originate from a compound ovary. The general and original usage of the term is less restrictive, and many nuts (in the culinary sense), such as
almond
The almond (''Prunus amygdalus'', syn. ''Prunus dulcis'') is a species of tree native to Iran and surrounding countries, including the Levant. The almond is also the name of the edible and widely cultivated seed of this tree. Within the genu ...
s,
pecans,
pistachio
The pistachio (, ''Pistacia vera''), a member of the cashew family, is a small tree originating from Central Asia and the Middle East. The tree produces seeds that are widely consumed as food.
''Pistacia vera'' is often confused with other spe ...
s,
walnuts, and
Brazil nut
The Brazil nut (''Bertholletia excelsa'') is a South American tree in the family Lecythidaceae, and it is also the name of the tree's commercially harvested edible seeds. It is one of the largest and longest-lived trees in the Amazon rainforest ...
s,
are not nuts in a botanical sense. Common usage of the term often refers to any hard-walled, edible kernel as a nut.
Nuts are an
energy-dense and
nutrient
A nutrient is a substance used by an organism to survive, grow, and reproduce. The requirement for dietary nutrient intake applies to animals, plants, fungi, and protists. Nutrients can be incorporated into cells for metabolic purposes or excre ...
-rich food source.
Botanical definition
A seed is the mature fertilised ovule of a plant; it consists of three parts, the
embryo
An embryo is an initial stage of development of a multicellular organism. In organisms that reproduce sexually, embryonic development is the part of the life cycle that begins just after fertilization of the female egg cell by the male spe ...
which will develop into a new plant, stored food for the embryo, and a protective seed coat.
Botanically
Botany, also called , plant biology or phytology, is the science of plant life and a branch of biology. A botanist, plant scientist or phytologist is a scientist who specialises in this field. The term "botany" comes from the Ancient Greek w ...
, a nut is a fruit with a woody
pericarp developing from a syncarpous
gynoecium
Gynoecium (; ) is most commonly used as a collective term for the parts of a flower that produce ovules and ultimately develop into the fruit and seeds. The gynoecium is the innermost whorl of a flower; it consists of (one or more) '' pist ...
. Nuts may be contained in an
involucre, a cup-shaped structure formed from the flower
bract
In botany, a bract is a modified or specialized leaf, especially one associated with a reproductive structure such as a flower, inflorescence axis or cone scale. Bracts are usually different from foliage leaves. They may be smaller, larger, or o ...
s. The involucre may be scaly, spiny, leafy or tubular, depending on the species of nut.
Most nuts come from the
pistils with ''inferior'' ovaries (see
flower
A flower, sometimes known as a bloom or blossom, is the reproductive structure found in flowering plants (plants of the division Angiospermae). The biological function of a flower is to facilitate reproduction, usually by providing a mechanis ...
) and all are ''indehiscent'' (not opening at maturity). True nuts are produced, for example, by some plant families of the
order
Order, ORDER or Orders may refer to:
* Categorization, the process in which ideas and objects are recognized, differentiated, and understood
* Heterarchy, a system of organization wherein the elements have the potential to be ranked a number of ...
Fagales. These include
beech
Beech (''Fagus'') is a genus of deciduous trees in the family Fagaceae, native to temperate Europe, Asia, and North America. Recent classifications recognize 10 to 13 species in two distinct subgenera, ''Engleriana'' and ''Fagus''. The ''Engl ...
(''Fagus''),
chestnut
The chestnuts are the deciduous trees and shrubs in the genus ''Castanea'', in the beech family Fagaceae. They are native to temperate regions of the Northern Hemisphere.
The name also refers to the edible nuts they produce.
The unrel ...
(''Castanea''),
oak (''Quercus''),
stone-oak (''Lithocarpus'') and
tanoak (''Notholithocarpus'') in the family
Fagaceae
The Fagaceae are a family of flowering plants that includes beeches, chestnuts and oaks, and comprises eight genera with about 927 species. Fagaceae in temperate regions are mostly deciduous, whereas in the tropics, many species occur as ever ...
, as well as
hazel
The hazel (''Corylus'') is a genus of deciduous trees and large shrubs native to the temperate Northern Hemisphere. The genus is usually placed in the birch family Betulaceae,Germplasmgobills Information Network''Corylus''Rushforth, K. (1999). ...
,
filbert (''Corylus'') and
hornbeam (''Carpinus'') in the family
Betulaceae.
Also widely known as nuts are dry
drupe
In botany, a drupe (or stone fruit) is an indehiscent fruit in which an outer fleshy part ( exocarp, or skin, and mesocarp, or flesh) surrounds a single shell (the ''pit'', ''stone'', or ''pyrena'') of hardened endocarp with a seed (''kernel ...
s, which include
pecans (''Carya illinoensis''),
almond
The almond (''Prunus amygdalus'', syn. ''Prunus dulcis'') is a species of tree native to Iran and surrounding countries, including the Levant. The almond is also the name of the edible and widely cultivated seed of this tree. Within the genu ...
s (''Prunus amygdalus''),
macadamia (''Macadamia integrifolia''),
candlenut (''Aleurites moluccanus''),
water caltrop (''Trapa bicornis'') and
walnuts (''Juglans regia''). A drupe is an
indehiscent fruit which has an outer fleshy part consisting of the
exocarp, or skin, and
mesocarp, or flesh, which surround a single pit or stone, the
endocarp
Fruit anatomy is the plant anatomy of the internal structure of fruit. Fruits are the mature ovary or ovaries of one or more flowers. They are found in three main anatomical categories: aggregate fruits, multiple fruits, and simple fruits. Aggr ...
with a
seed
A seed is an embryonic plant enclosed in a protective outer covering, along with a food reserve. The formation of the seed is a part of the process of reproduction in seed plants, the spermatophytes, including the gymnosperm and angiosper ...
(kernel) inside. In a dry drupe, the outer parts dry up and the remaining husk is part of the ovary wall or
pericarp, and the hard inner wall surrounding the seed represents the inner part of the pericarp.
[
A small nut may be called a "nutlet" (or nucule, a term otherwise referring to the ]oogonium
An oogonium (plural oogonia) is a small diploid cell which, upon maturation, forms a primordial follicle in a female fetus or the female (haploid or diploid) gametangium of certain thallophytes.
In the mammalian fetus
Oogonia are formed in l ...
of stoneworts). In botany
Botany, also called , plant biology or phytology, is the science of plant life and a branch of biology. A botanist, plant scientist or phytologist is a scientist who specialises in this field. The term "botany" comes from the Ancient Greek w ...
, the term "nutlet" specifically refers to a pyrena
A pyrena or pyrene (commonly called a "pit" or "stone") is the fruitstone within a drupe or drupelet produced by the ossification of the endocarp or lining of the fruit. It consists of a hard endocarp tissue surrounding one or more seeds (al ...
or pyrene, which is a seed
A seed is an embryonic plant enclosed in a protective outer covering, along with a food reserve. The formation of the seed is a part of the process of reproduction in seed plants, the spermatophytes, including the gymnosperm and angiosper ...
covered by a stony layer, such as the kernel of a drupe
In botany, a drupe (or stone fruit) is an indehiscent fruit in which an outer fleshy part ( exocarp, or skin, and mesocarp, or flesh) surrounds a single shell (the ''pit'', ''stone'', or ''pyrena'') of hardened endocarp with a seed (''kernel ...
. 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.
In common use, a "tree nut" is, as the name implies, any nut coming from a tree. This most often comes up regarding food allergies; a person may be allergic specifically to peanuts (which are not tree nuts but legume
A legume () is a plant in the family Fabaceae (or Leguminosae), or the fruit or seed of such a plant. When used as a dry grain, the seed is also called a pulse. Legumes are grown agriculturally, primarily for human consumption, for livestock for ...
s), whereas others may be allergic to the wider range of nuts that grow on trees.
Production
In the 21st century, some dozen species constitute most of the worldwide production of nuts, shown in the table below for major commercial nuts.
Food and health effects
Nuts contain the diverse nutrients that are needed for the growth of a new plant.[ Composition varies, but they tend to have a low water and ]carbohydrate
In organic chemistry, a carbohydrate () is a biomolecule consisting of carbon (C), hydrogen (H) and oxygen (O) atoms, usually with a hydrogen–oxygen atom ratio of 2:1 (as in water) and thus with the empirical formula (where ''m'' may o ...
content, with high levels of fats, protein
Proteins are large biomolecules and macromolecules that comprise one or more long chains of amino acid residues. Proteins perform a vast array of functions within organisms, including catalysing metabolic reactions, DNA replication, res ...
, dietary minerals, and vitamin
A vitamin is an organic molecule (or a set of molecules closely related chemically, i.e. vitamers) that is an essential micronutrient that an organism needs in small quantities for the proper functioning of its metabolism. Essential nutrie ...
s.[ The digestibility of the protein at about 90% is slightly lower than that of meat and fish, but can be improved by thorough chewing.][ The fats are largely unsaturated and nuts are a source of essential ]omega-3 fatty acid
Omega−3 fatty acids, also called Omega-3 oils, ω−3 fatty acids or ''n''−3 fatty acids, are polyunsaturated fatty acids (PUFAs) characterized by the presence of a double bond, three atoms away from the terminal methyl group in their chem ...
s. As part of a healthy human diet, long-term consumption of diverse nutrients in nuts may contribute to a lower risk of cardiovascular diseases, reduced levels of blood cholesterol, and lower all-cause mortality.[ For vegetarians and ]vegans
Veganism is the practice of abstaining from the use of animal product—particularly in diet—and an associated philosophy that rejects the commodity status of animals. An individual who follows the diet or philosophy is known as a vegan. Di ...
, nuts provide many of the essential nutrients which may be in short supply in other plant food
A fertilizer (American English) or fertiliser (British English; see spelling differences) is any material of natural or synthetic origin that is applied to soil or to plant tissues to supply plant nutrients. Fertilizers may be distinct from ...
s.
Nuts supply nutrients for humans and wildlife.[ Because nuts generally have a high oil content, they are a significant energy source.][ Many seeds are edible by humans and used in cooking, eaten raw, sprouted, or roasted as a ]snack food
A snack is a small portion of food generally eaten between meals. Snacks come in a variety of forms including packaged snack foods and other processed foods, as well as items made from fresh ingredients at home.
Traditionally, snacks are ...
, ground to make nut butters, or pressed for oil that is used in cooking and cosmetics.[ Moderate nut consumption about per week may benefit weight control and contribute to lowering body weight in humans.][
Nuts used for food are a common source of food allergens.][ Reactions can range from mild symptoms to severe ones, a condition known as ]anaphylaxis
Anaphylaxis is a serious, potentially fatal allergic reaction and medical emergency that is rapid in onset and requires immediate medical attention regardless of use of emergency medication on site. It typically causes more than one of the follo ...
, which can be life-threatening. The reaction is due to the release of histamine
Histamine is an organic nitrogenous compound involved in local immune responses, as well as regulating physiological functions in the gut and acting as a neurotransmitter for the brain, spinal cord, and uterus. Since histamine was discover ...
by the body in response to an allergen
An allergen is a type of antigen that produces an abnormally vigorous immune response in which the immune system fights off a perceived threat that would otherwise be harmless to the body. Such reactions are called allergies.
In technical t ...
in the nuts, causing skin and other possible reactions. Many experts suggest that a person with an allergy to peanuts should avoid eating tree nuts, and vice versa.[
]
Nutrition
Constituents
Nuts are the source of energy and nutrients for the new plant. They contain a relatively large quantity of calories, essential unsaturated and monounsaturated fats including linoleic acid
Linoleic acid (LA) is an organic compound with the formula COOH(CH2)7CH=CHCH2CH=CH(CH2)4CH3. Both alkene groups are ''cis''. It is a fatty acid sometimes denoted 18:2 (n-6) or 18:2 ''cis''-9,12. A linoleate is a salt or ester of this acid.
...
and linolenic acid
Linolenic acid is a type of naturally-occurring fatty acid. It can refer to either of two octadecatrienoic acids (i.e. with an 18-carbon chain and three double bonds, which are found in the '' cis'' configuration), or a mixture of the two. Linol ...
, vitamins, and essential amino acids.[ Many nuts are good sources of ]vitamin E
Vitamin E is a group of eight fat soluble compounds that include four tocopherols and four tocotrienols. Vitamin E deficiency, which is rare and usually due to an underlying problem with digesting dietary fat rather than from a diet low in vi ...
, vitamin B2, folate
Folate, also known as vitamin B9 and folacin, is one of the B vitamins. Manufactured folic acid, which is converted into folate by the body, is used as a dietary supplement and in food fortification as it is more stable during processing an ...
, fiber
Fiber or fibre (from la, fibra, links=no) is a natural or artificial substance that is significantly longer than it is wide. Fibers are often used in the manufacture of other materials. The strongest engineering materials often incorporate ...
, and essential minerals, such as magnesium, phosphorus, potassium, copper, and selenium.[
This table lists the percentage of various nutrients in four unroasted seeds.
]
Research
Nuts are under preliminary research to assess whether their consumption may lower risk for some diseases, such as cardiovascular diseases and cancer. A 2014 review indicated that consuming one or more servings of nuts or peanut butter
Peanut butter is a food paste or spread made from ground, dry-roasted peanuts. It commonly contains additional ingredients that modify the taste or texture, such as salt, sweeteners, or emulsifiers. Peanut butter is consumed in many countri ...
per day could lower the risk of ischemic heart disease
Coronary artery disease (CAD), also called coronary heart disease (CHD), ischemic heart disease (IHD), myocardial ischemia, or simply heart disease, involves the reduction of blood flow to the heart muscle due to build-up of atherosclerotic pl ...
, overall cardiovascular disease, stroke in women, and all-cause mortality. A 2022 umbrella review confirmed these findings and found a 22% reduction in all-cause mortality.
See also
Notes
References
Further reading
*Albala, Ken (2014) ''Nuts A Global History''. The Edible Series.
External links
*
{{Authority control
Fruit morphology
Snack foods
Vegan cuisine
Vegetarian cuisine
Christmas food
Staple foods
Types of food