nut (fruit)

A nut is a

fruit

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 seeds 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

s,

chestnut

s, and

acorn

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

s,

pecan

s,

pistachio

s,

walnut

s, 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. Nuts are an energy-dense and nutrient-rich food source.

Botanical definition

A seed is the mature fertilised ovule of a plant; it consists of three parts, the

embryo

which will develop into a new plant, the endosperm which contains nutrients, and a protective seed coat.

Botanically

, a nut is a seed which has a large proportion of endosperm and a tough seed coat which becomes increasingly hard as the nut matures. One or a few nuts may be contained in an involucre, a cup-shaped structure formed from the flower

bract

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

) and all are ''indehiscent'' (not opening at maturity). True nuts are produced, for example, by some plant families of the order Fagales. These include

beech

(''Fagus''),

chestnut

(''Castanea''),

oak

(''Quercus''), Stone-oak,(''Lithocarpus'') and tanoak (''Notholithocarpus'') in the family Fagaceae, as well as

hazel

,

filbert

(''Corylus'') and hornbeam (''Carpinus'') in the family Betulaceae.

Also widely known as nuts are dry drupes, which include

pecan

s (''Carya illinoensis''),

almond

s (''Prunus amygdalus''),

macadamia

(''Macadamia integrifolia''), candlenut (''Aleurites moluccanus''), water caltrop (''Trapa bicornis'') and

walnut

s (''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 with a

seed

(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 of

stoneworts

). In

botany

, the term "nutlet" 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.

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

s), whereas others may be allergic to the wider range of nuts that grow on trees.

Production

In the 21st century, some dozen nuts comprise most of worldwide production, 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 content, with high levels of fats, protein, dietary minerals, and vitamins. 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 acids. 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, nuts provide many of the essential nutrients which may be in short supply in other plant foods.

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, 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, which can be life-threatening. The reaction is due to the release of

histamine

by the body in response to an allergen 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

and linolenic acid, vitamins, and essential amino acids. Many nuts are good sources of

vitamin E

, vitamin B₂, folate, fiber, 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 per day could lower the risk of ischemic heart disease, overall cardiovascular disease, stroke in women, and all-cause mortality.

See also

*

* List of culinary nuts
* List of edible seeds
* List of foods
*

Nutmeg

*

Achene

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