Medically reviewed on June 7, 2018
What is Walnut?
There are about 15 species of Juglans (walnut genus); commercially, J. regia is the most important. This deciduous tree can grow to 45 m in height. J. regia is native to Asia but is cultivated now in France and other parts of Europe, North Africa, North America, and East Asia.
Juglans regia L. Family: Juglandaceae
Walnut, English walnut, Persian walnut, Caucasian walnut, Circassian walnut, and European walnut.
What is it used for?
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. 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.
Historically, walnut oil was prescribed for colic, to soothe intestines, and to relieve diarrhea and hemorrhoids. Further folk uses include treating rickets, frostbite, and glandular disturbances, and as an astringent, tonic restorative, and disinfectant. Blisters, ulcers, itchy scalp/dandruff, sunburn, and perspiration are some of the conditions treated with various walnut preparations.
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.
What is the recommended dosage?
Daily dosages used in clinical trials range from 20 to 84 g/day (1 shelled walnut is approximately 5 g).
Contraindications have not been identified. Cross-hypersensitivity between tree nuts is known to exist.
Generally recognized as safe when used as food. The possibility of in utero sensitization has been debated without conclusion.
None well documented. Walnut interferes with the absorption of iron.
Allergy and fatal anaphylaxis to walnut have been reported.
Information is lacking. Juglone, a constituent of walnut, is toxic in animals.