Walnut

Scientific Name(s): Juglans nigra L., Juglans regia L.
Common Name(s): American walnut, Black walnut, Caucasian walnut, Circassian walnut, English walnut, European walnut, Persian walnut

Medically reviewed by Drugs.com. Last updated on May 9, 2022.

Clinical Overview

Use

The inclusion of walnuts in the diet is recommended as a dietary source of polyunsaturated fatty acids and other nutrients, and to improve the lipid profile in hyperlipidemic individuals. Cardiac benefits of walnut consumption are described. Walnuts have also been studied in metabolic syndrome with limited benefit demonstrated. The effect of walnut extract in Alzheimer disease is being investigated.

Dosing

Daily dosages used in clinical trials range from 20 to 84 g/day (4 shelled walnuts equal approximately 20 g).

Contraindications

Contraindications have not been identified. Cross-hypersensitivity between tree nuts is known to exist.

Pregnancy/Lactation

White walnut is generally recognized as safe when used as food; the possibility of in utero sensitization has been debated without conclusion.

Avoid use of black walnut preparations. Documented adverse reactions (mutagenic properties). Possible cathartic effects have been observed at higher doses.

Interactions

None well documented. Walnut interferes with the absorption of iron.

Adverse Reactions

Allergy and fatal anaphylaxis to walnut have been reported.

Toxicology

Information is lacking. Juglone, a constituent of walnut, is toxic in animals.

Scientific Family

• Juglandaceae (walnut)

Botany

There are approximately 15 species of Juglans walnuts. "Walnut" refers to several varieties, most commonly the English walnut (J. regia) and the black walnut (J. nigra). Walnut trees have short trunks with round-topped crowns and can grow up to 45 m in height. The black walnut is native to the deciduous forests of the eastern United States (central Mississippi and Appalachian regions) and Canada. Walnut tree leaves are compound and between 15 and 30 cm long. The male flowers are long, drooping catkins, while the female flowers are short spikes. Walnut trees self-pollinate and cross-pollinate. J. regia is native to Asia but is now cultivated in France and other parts of Europe, North Africa, North America, and East Asia.1 The wood is valued for its rich beauty and is used to make furniture, cabinets, and gun stocks. The black walnut fruit is an elongated drupe containing a 4-ribbed edible nut within a thick, hard, black shell that is smaller than the English walnut.1, 2

History

Walnuts have been found in prehistoric deposits in Europe dating from the Iron Age and are mentioned in Old Testament references to King Solomon's nut garden. The genus name Juglans comes from the Latin Jovis glans, meaning "nut of Jupiter" or "nut of the Gods." Many legends have been associated with the walnut; the ancient Greeks and Romans regarded them as symbols of fertility. In the Middle Ages, walnuts were thought to ward off witchcraft, the evil eye, and epileptic fits because of the belief that evil spirits lurked in the walnut branches.3

Historically, walnut oil was prescribed for colic, to soothe intestines, and to relieve diarrhea and hemorrhoids.3, 4, 5 Further folk uses include treating rickets, frostbite, and glandular disturbances, and as an astringent, tonic restorative, and disinfectant.6, 7 Some cultures use walnut b...