We know that legumes, nuts and seeds can be some of the healthiest superfoods around when consumed in moderation, and one of the better nuts for health is the walnut. Walnuts nutrition has been shown to help fight depression, improve brain health, boost heart health and more. But did you know there’s a type of walnut in particular, the black walnut, that provides some remarkable benefits of its own?
The black walnut has been a nutritious addition to the diets of individuals since ancient times, from the Native American to Asian cultures. Studies have focused on the constituents, flavonoids, quinones and polyphenols found in the kernels, which are known for their antineoplastic, anti-inflammatory, antioxidant, antiatherogenic and neuroprotective properties.
Given that, black walnuts are a popular superfood, and modern research is only just scratching the surface when it comes to uncovering the powerful nutritional components these unique nuts contain, as I describe below. (1)
What Is Black Walnut?
Black walnut (Juglans nigra), also known as American walnut, is a large hardwood species in the Juglandacea family and native to eastern North America before spreading westward toward California. With heights reaching up to 100 feet and deep roots as long as 10 feet, it adds to the stability and support for the black walnut tree but makes it difficult to soak up water.
This is the reason why black walnuts can be found growing in regions with occasional rainfall or near creek beds. The leaves are spear-shaped, light-green and several inches in length. The bark is black, deeply furrowed, thick and reveals a dark-covered subsurface when scraped.
The tree is native to the Himalayas, Kyrgyzstan, Central Asia and was cultivated in Europe as early as 100 B.C. The black walnut tree also has been historically used to get rid of a fever and treat kidney ailments, gastrointestinal concerns, ulcers, toothache, snake bites and syphilis.
Recent studies have shown that the husks of the black walnut contain chemicals that inhibit bacterial and fungal growth and may be valuable in controlling dermal, mucosal and oral infections in humans.
1. Expels Parasites
One of the key active components of the black walnut hull is juglone. Juglone exerts its effect by inhibiting certain enzymes needed for metabolic function. It’s highly toxic to many insect herbivores — it’s often used by organic gardeners as a natural pesticide — and researchers have observed that black walnut can expel parasitic worms from the body.
According to the Pharmaceutical Society of Australia, black walnut is effective against ringworm, tapeworm, pin or thread worm, and other parasites of the intestine. (2) This is why black walnut makes a great addition to any parasite cleanse.
2. Promotes Healthy Skin
The tannins in black walnut have an astringent effect, which is used to tighten the epidermis, mucous membranes and relieve irritation. Dermatological applications associated with black walnut include viral warts, eczema, acne, psoriasis, xerosis, tinea pedis and poison ivy. (3)
3. Improves Cardiovascular Health
Black walnuts are an excellent source of alpha-linolenic acid (ALA), with 100 grams of the walnuts containing 3.3 grams of ALA. (4) Walnuts are an excellent staple of the Mediterranean diet food list, a diet thought to be healthy in reducing mortality rates from coronary artery disease, which is low in Mediterranean populations.
Recent epidemiological studies suggest that frequent consumption of walnuts may have protective effects against coronary heart disease because of the promising effects on blood lipid profiles. In clinical studies, diets supplemented with walnuts decreased serum concentration of low-density lipoprotein and cholesterol.
Other potential protective constituents include high amounts of magnesium, vitamin E, protein, dietary fiber, potassium and alpha-linolenic acid. (5)
4. Holds Antifungal and Antimicrobial Activity
The juice from unripe black walnut hulls has been used in folk medicine for many years as a treatment for topical, localized dermatophytic fungal infections, such as ringworm. These fungal infections usually involve the keratinized tissues, such as hair, skin and nails. Such infections may be chronic and resistant to treatment but rarely affect the general health of the patient.
It’s been suggested that the biological activity of the black walnut hull is due to the naphthoquinone, juglone (5-hydroxy-1,4 naphthoquinone). The antifungal activity of juglone has also been compared to other known antifungal agents, such as griseofulvin, clotrimazole, tolnaftate, triacetin, zinc undecylenate, selenium sulfide, liriodenine and liriodenine methionine.
In a study, it was determined that juglone exhibited moderate antifungal activity similar to zinc undecylenate and selenium sulfide, which are commercially available antifungal agents (6). Internally, black walnut is also used for chronic constipation, intestinal toxemia, portal congestion, hemorrhoids and giardia.
The derivatives of 1,4-naphthoquinons have been of great clinical interest since these compounds exhibit strong activity as antibacterial and antifungal agents. A series of 50 naphthoquinone derivatives was synthesized and evaluated for antibacterial and antifungal properties, with highest activity against S. aureus and candida symptoms and moderate activity against gram-positive and acid-fast bacteria.
Another study showed that juglone potentially can inhibit three key enzymes from Helicobacter pylori, a gram-negative bacterium that causes several human gastrointestinal diseases. Several algae species, including Anabaena variabilis and Anabaena flos-aquae, were inhibited significantly by juglone as well. (7)
5. Helps Protect Against Cancer
Quinones have been associated with anticancer activity. Juglone is a quinone found in the leaves, roots and bark of black walnut trees. The exocarp of immature green fruit, bark and branches has been used in China to treat liver, lung and gastric cancer. Juglone blocks potassium channels, promotes the generation of hydrogen peroxide and inhibits transcription in cancer cells.
In a recent study, it was shown to promote cell death in human colorectal cells, and given black walnuts juglone content, it could make the black walnut a potential cancer-fighting food. (8)
Black walnut leaves, bark and fruits contain a constituent called juglone, aka 5-hydroxy-1,4-naphthalenedione, an active constituent known to be effective against worms, tobacco mosaic virus and H-pylori.
Plumbagin, or 5-hydroxy-2-methyl-1,4-naphthoquinone, is a quinoid constituent that’s also found in Juglans nigra. Plumbagin has been known for its potential health benefit in being neuroprotective. It inhibits ectopic growth of human breast cancer, melanoma and non-small cell lung cancer cells. It’s been reported the plumbagin induces apoptosis, inhibiting growth of prostate and pancreatic cancer cells. (9)
Plumbagin was evaluated for antimalarial activity against Anopheles stephensi Liston, a mosquito vector of malaria. After the three-hour exposure period, larval mortality was observed against A. stephensi. The results, published in Parasitology Research, show that plumbagin may be considered as a new potential source of natural larvicide for the control of malaria. (10)
Other constituents found in black walnut include: (11)
- 1-alpha-tetralone derivative
Black walnut also contains higher amounts of antioxidants, polyphenols and monounsaturated fatty acids, such as gamma-tocopherol. These components have been correlated with the prevention and/or treatment of several types of diseases, including neurodegenerative conditions, cancer and diabetes.
Other nutrients that are also present in the black walnut include folate, melatonin and phytosterols. Based upon its phytochemical and phytonutrient composition, the black walnut is a potentially potent and a beneficial addition in diets in order to promote overall health.
In addition, one ounce (28 grams) of black walnuts contains about: (12)
- 173 calories
- 2.8 grams carbohydrates
- 6.7 grams protein
- 16.5 grams fat
- 1.9 grams fiber
- 1.1 milligrams manganese (55 percent DV)
- 0.4 milligram copper (19 percent DV)
- 56.3 milligrams magnesium (14 percent DV)
- 144 milligrams potassium (14 percent DV)
- 0.2 milligram vitamin B6 (8 percent DV)
- 4.8 microgram selenium (7 percent DV)
- 0.9 milligram zinc (6 percent DV)
- 0.9 milligram iron (5 percent DV)
How to Use and Cook
The vast majority of walnuts purchased in stores are English walnuts, which are easier to crack and larger than black walnuts. In some places, black walnuts can be purchased in stores or at a reputable online store.
The meat encased in the black walnut is much smaller and more difficult to pick out of the shell compared to other walnuts. For this reason, black walnuts are chopped. One reason people would leave black walnut alone is that it’s literally a tough nut to break. Aside from using a huller, people find other ways to crack the shell, such as a hammer or a rock. (13)
Once the nuts are hulled, they need to dry for a few weeks before cracking. A rule of thumb is to leave them until you can hear the nuts rattle when you shake it.
If living in one of the states where black walnuts grow, these can be purchased at the local farmer’s market. These nuts can keep for a year in refrigeration and up to two years in the freezer.
If living in an area lacking in black walnut trees, it’s easy enough during the fall season to find black walnuts under the Hammons label at supermarket chains. At other times of year, black walnuts can be found under stores’ private labels or other national brand names. Either way, the nuts most likely came from Hammons. Black walnuts can also be purchased at a reputable online store, already shelled. (14)
Predominantly green hulls in black walnut are more effective than hulls that were darker in color when harvesting or reading the supplement label. Black walnuts can be taken as a fresh plant liquid extract, one to 10 drops, one to three times per day in a little water. (15)
Black walnuts have a long history in medicinal use and are one of the most versatile nuts in the world. The hulls are used to make a natural plant dye, with shades of deep brown, light brown or cream. The wood is very attractive, heavy and hard, making it the easiest type of wood to work with.
The major use for black walnut today is for the home to make interior finishing, cabinets, furniture and veneers. Black walnut also was the preferred choice wood for gunstocks, popular among the gunsmiths in Pennsylvania using it for long rifles. (16)
Cleaned and processed, black walnut shells were used as abrasives in filter materials. Researchers at Columbia University reported that extracts from the green hull in black walnut are capable of paralyzing mice, fish, rabbits and rats, which is currently illegal.
A Roman naturalist named Pliny the Elder discovered the healing power of black walnuts in the first century A.D. Herbalist Nicholas Culpeper prescribed walnut to draw poisonous venom from snake and spider bites in the 17th century.
Native Americans used the bark, leaves, husk and nuts from black walnut trees medicinally, particularly as a mosquito repellant and to treat skin conditions and psychological disorders. They were also the first to use hulls as a natural laxative and for eliminating parasites in the intestine, which is the most commonly implemented today.
Black walnut continues to be a versatile and popular functional food as it was thousands of years ago. These walnuts are a delicious and favored addition in many culinary creations. Crack open the nuts, save the meat for cooking and eating, and crush the hulls into a powder to use them. You can also try black walnuts in soups, sprinkled on top of salads and baked into casseroles to experience a whole new flair in cooking.
Risks and Side Effects
When it comes to the topical application for skin conditions, potential side effects of black walnut are few. Due to the astringent action of the tannins, black walnut causes the top layer of the skin to become dehydrated and forms a thick layer of dense tissue similar to a callus.
For patients with nut allergies, an allergic reaction to black walnut may result in rashes, itchy and swollen skin, hives, chest pain, or problems with breathing.
When taking any medications, herbs or supplements, it’s recommended to wait at least two hours after the consumption of black walnut because it may bind to other medications when taken at the same time. Caution is advised in patients who take blood pressure measure medication because black walnut may alter the drug.
Black walnut may have additive effects with antimicrobials and laxatives. Caution is also advised when taking herbs, medications or supplements used for nausea, gastrointestinal issues, inflammation, cancer, along with herbs, supplements and medication that harm the kidney or liver or herbs and supplements that contain tannins.
Black walnut is not recommended for pregnant or breastfeeding women or for extended periods of time.
The fresh green husk can cause irritation and blistering when applied to the skin in excessive quantities. Taken internally in large doses, it’s a sedative to the circulation system and heart. (17)
- Black walnuts were introduced to Europe in the mid-1600s and are now cultivated across North America in tree plantations for their prized dark-colored wood. They’re also a popular delicacy in North America and Europe and can be found in everything from casseroles to pasta and salads.
- Black walnut has been shown to destroy certain cancer cells and treat colic, regulate digestion, and improve immunity, flatulence and respiratory conditions.
- Specifically, this herb has been proven to beat malaria, improve cardiovascular health, get rid of parasites, contain antimicrobial and antifungal abilities, and treat skin conditions.
- Black walnut is commercially available at health stores and online as a liquid extract and in capsule form.
- Black walnut should only be taken under the supervision of a health care professional. It should always be taken in small doses as directed and not for an extended period of time.