Scientific Name(s): Juglans regia L. Family: Juglandaceae
Common Name(s): English walnut , Persian walnut , Caucasian walnut , Circassian walnut , European walnut
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.
Daily dosages used in clinical trials range from 20 to 84 g/day (4 shelled walnuts equal approximately 20 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.
There are 15 species of Juglans ; commercially, J. regia is the most important. This deciduous tree can grow to 45 m in height. The trunk is straight and clear, with silvery-gray bark. The crown of the tree is open and round-topped. 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
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. 2
Historically, walnut oil was prescribed for colic, to soothe intestines, and to relieve diarrhea and hemorrhoids. 2 , 3 , 4 Further folk uses include treating rickets, frostbite, and glandular disturbances, and as an astringent, tonic restorative, and disinfectant. 5 , 6 Some cultures use walnut bark for cleaning the teeth, possibly improving oral hygiene because it increases the pH of saliva. 7 Walnut may possess anti-helminthic activity. 6 It is considered helpful in inflammatory conditions, including rheumatoid arthritis, and certain skin disorders. Blisters, ulcers, itchy scalp/dandruff, sunburn, and perspiration are some of the conditions treated with various walnut preparations. 5
Walnuts are a common food source and are used in cooking and baking. 2 , 8 Walnut extract is an old-fashioned hair dye and also has been used to darken (stain) the skin. 5 , 8 Walnut shell flour has been used as a carrier for insecticides, filler for building materials, and stuffing in toys. 8
Walnuts contain 3% to 4% water, 60% oil, and 15% to 20% protein, bearing approximately 700 calories per 100 g. 8 The mineral content includes iron and zinc (approximately 3 mg per 100 g each), sodium (2 mg per 100 g), selenium (19 mcg per 100 g), calcium, magnesium, potassium, copper, and phosphorus. 6 , 8 , 9 Vitamins E and C also are found in walnut. 4 , 10
Walnuts differ from other nuts in that they predominantly contain the polyunsaturated fatty acids alpha linolenic (n-3) acid and linoleic (n-6) acid, rather than mono-unsaturated fatty acids. 11 , 12 L-arginine (a precursor to nitric oxide) is also found in significant amounts in walnuts. 11
The chief known chemical constituent in walnut is juglone (5-hydroxy-1,4-naphthagulone). Also present are alpha-hydrojuglone (1,4,5-trihydroxynaphthalene) and its glycoside beta-hydrojuglone, along with caffeic acid, ellagic acid, hyperin, and kaempferol, and the tannins galloylglucose and ellagitannins. 5 , 8 In one report, 45 volatile compounds were isolated from whole green walnuts. 13 Gamma lactones are present in walnut oils. 14
Uses and PharmacologyLipid profile and cardiovascular effects
Clinical trials conducted in healthy adults 11 , 15 , 16 , 17 , 18 , 19 and in patients with type 2 diabetes 20 , 21 and metabolic syndrome 22 , 23 , 24 have been critically reviewed. 12 , 25 Studies in patients with heart disease are lacking. 25
The majority of studies show a reduction of total cholesterol and low-density lipoprotein–cholesterol to cardioprotective levels. Effects on high-density lipoprotein–cholesterol are inconsistent, as are those for triglycerides. The diminishing positive effects observed may be a consequence of increased fat intake with higher dosages used (and lesser effects due to lower dosages). 12 , 25
The role of walnut in atherosclerosis is unclear. Improved endothelial function has been demonstrated, possibly due to alpha linolenic acid or L-arginine content. 11 , 26 In another study, walnut activated the nuclear transcription factor identified in human atherosclerotic plaques in healthy men. 27
Results of studies investigating the effects of walnuts on oxidative stress and apoprotein response are variable. 22 , 25 , 27 There is general agreement that no gain in body weight results from the addition of walnuts to the diet. 16 , 20 , 25Other effects
Walnut extract was demonstrated to inhibit and defibrillize amyloid beta protein—a feature of the amyloid plaque seen in the brains of patients with Alzheimer disease. 28Antimicrobial
A study from China found borneol-walnut oil to be superior to neomycin in treating otitis media without any toxic effects. 29 The constituent juglone has been demonstrated to possess antimicrobial and antifungal effects. 7
Walnut leaves have been approved by the German Commission E for external application for excessive perspiration and skin inflammation. 32
Generally recognized as safe when used as food. The possibility of in utero sensitization has been debated. 33
None well documented. Walnut interferes with the absorption of iron. 25
Allergies to nuts are common in the United States (an estimated 1%), 34 with walnut and other tree nut allergy considered to be second only to peanuts (a legume) in anaphylactic reactions. However, cross-reactivity to the proteins from tree nuts among peanut-allergic people is considered low. A co-allergy is probably the cause of allergic reactions among atopic individuals. 33 , 34 Cross-reactivity between walnut and peach lipid transfer protein allergen has been noted. 35 , 36 , 37
Fatalities from anaphylaxis to walnuts have been recorded. 35
Bibliography1. Juglans regia L. USDA, NRCS. 2007. The PLANTS Database ( http://plants.usda.gov, 28 Oct 2007 ). National Plant Data Center, Baton Rouge, LA 70874-4490 USA.
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