Black walnuts are celebrated for their bold, earthy flavor and impressive nutrient profile.

They have been associated with many health benefits like reduced heart disease risk and weight loss.

The antioxidant and antibacterial compounds in their outer shells, or hulls, make them useful for naturally treating parasitic and bacterial infections.

This article reviews the benefits, uses, and potential safety concerns of black walnuts.

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Black walnuts, or Juglans nigra, grow wild across the United States and are the second most cultivated walnut in North America, following English walnuts.

They consist of a kernel, a dry outer covering known as a hull, and a hard shell.

The kernel is the part of the walnut that’s commonly eaten raw or roasted and can be pressed for oil. The hulls contain antioxidants and are used in extracts and supplements for medicinal purposes, such as to treat parasitic infections or decrease inflammation (1).

Black walnuts have a unique flavor and aroma, making them bolder and earthier than English walnuts. They’re a popular addition to recipes like baked goods and desserts.

Summary Black walnuts are the second most common walnut and prized for their bold and earthy flavor. The nutrients in the hulls are extracted and used in supplements.

Black walnuts are high in protein, healthy fats, and many vitamins and minerals.

A 1-ounce (28-gram) serving of black walnuts contains (2):

  • Calories: 170
  • Protein: 7 grams
  • Fat: 17 grams
  • Carbs: 3 grams
  • Fiber: 2 grams
  • Magnesium: 14% of the Reference Daily Intake (RDI)
  • Phosphorus: 14% of the RDI
  • Potassium: 4% of the RDI
  • Iron: 5% of the RDI
  • Zinc: 6% of the RDI
  • Copper: 19% of the RDI
  • Manganese: 55% of the RDI
  • Selenium: 7% of the RDI

Black walnuts are 75% higher in protein than English walnuts, which provide 4 grams of protein per 1-ounce (28-gram) serving. Protein is a nutrient that positively affects weight loss, blood sugar control, and feelings of fullness (2, 3).

They’re low in carbs, and most of the carbs come from fiber, a nutrient that may also promote feelings of fullness and weight control (4).

Walnuts are a good source of antioxidants — substances that can prevent or delay cellular damage caused by unstable molecules called free radicals.

For example, they contain proanthocyanidins, which may protect against sun damage, improve vision, and increase blood circulation (1).

They also provide alpha-linolenic acid (ALA), a type of omega-3 fatty acid. ALA is an essential fat, meaning that your body can’t produce it, so you need it from your diet.

ALA has been linked to several health benefits, including a reduced risk of heart disease and stroke (5, 6).

Summary Black walnuts are a nutrient-dense food — low in carbs and high in protein, antioxidants, and omega-3 fatty acids.

The fiber, omega-3 fatty acids, and antioxidants in black walnuts provide various health benefits. In addition, black walnut hulls have unique antibacterial properties and are used in herbal medicine extracts and supplements.

Black walnuts are nutritionally similar to English walnuts, which have been studied extensively for their health benefits.

May benefit heart health

Black walnuts contain various nutrients and compounds that benefit heart health, including:

  • Omega-3 fatty acids. May improve certain heart disease risk factors like high blood pressure and cholesterol levels (7).
  • Tannins. Help lower blood pressure and decrease blood lipid levels, potentially improving heart health (8).
  • Ellagic acid. May help prevent a narrowing of the arteries caused by plaque buildup that can lead to heart disease (9).

A review of 13 studies found that eating walnuts decreased total and LDL (bad) cholesterol. What’s more, studies show that eating walnuts improves blood vessel function and reduces the risk of plaque buildup, a major risk factor for heart disease (10, 11).

May have anticancer properties

Black walnuts contain an antitumor compound called juglone. Test-tube studies have found this compound to significantly reduce tumor growth (12, 13, 14).

Several test-tube studies indicate that juglone can cause cell death in certain cancerous cells, including of the liver and stomach (15, 16, 17).

In addition, black walnuts contain flavonoid antioxidants that have been shown to have beneficial effects against lung, breast, prostate, and colon cancer (18).

Have antibacterial properties

Black walnut hulls are high in tannins — compounds with antibacterial properties (8).

Tannins in black walnuts have antibacterial effects against, for example, Listeria, Salmonella, and E. coli — bacteria that commonly cause foodborne illnesses (19).

A test-tube study found that black walnut hull extracts have antioxidant and antibacterial activities, preventing the growth of Staphylococcus aureus, a bacteria that can cause infections (20).

May aid weight loss

Studies show that eating nuts — particularly walnuts — may help you lose weight (21, 22).

Though walnuts are high in calories, most of these calories come from healthy fats. Fats can help increase feelings of fullness and fend off hunger (2, 23).

In fact, walnuts have been found to keep you fuller for longer, which can help you naturally eat less, potentially promoting weight loss (24).

In one 3-month study, people who ate 1/4 cup (30 grams) of walnuts daily experienced greater weight loss than the control group — despite the additional calories of the walnuts (25).

Summary Black walnuts may have anticancer effects and promote heart health and weight loss. Additionally, plant compounds in the hulls have antioxidant and antibacterial properties.

Plant compounds in black walnut hulls are extracted and used as supplements in the form of capsules or liquid drops.

Due to its antibacterial properties, black walnut extract is used in wormwood complex supplements. Wormwood complex is a tincture made from black walnut hulls, a plant called wormwood, and cloves. It’s a natural remedy against parasitic infections.

Some people use the extract as a gargle to kill bacteria in their mouth. Extract from black walnut leaves can also be used to treat skin conditions, such as eczema, psoriasis, and warts (26, 27).

What’s more, the hull extract is used as a dye for hair, skin, and clothing due to the tannins, which have a natural darkening effect.

Both black walnut extract and wormwood complex supplements are widely available in stores and online.

That said, research is limited on black walnut extract for these uses, and more studies are needed to validate the benefits and side effects of black walnut supplements.

Summary The extracts from black walnut hulls are popular in herbal medicine and are used to treat parasitic infections. It can also be used as a gargle and as a natural dye.

Although black walnuts have many health benefits, there are some safety aspects to consider when eating them or taking them as a supplement.

People with any nut or tree nut allergy should not eat black walnuts or use supplements that contain them.

Supplements are not regulated by the Food and Drug Administration (FDA). Therefore, you should purchase them from reputable brands that offer products that are independently tested for safety and potency.

Research on the effects of black walnut supplements during pregnancy or while breastfeeding is insufficient, and it’s unknown whether it’s safe to take these supplements during pregnancy or lactation.

Additionally, the tannins in black walnuts may interact with certain medications. It’s best to consult with your healthcare provider before taking black walnut extract if you take medications or are pregnant or breastfeeding (28).

Summary People who are pregnant or breastfeeding, allergic to nuts, or on certain medications should not take black walnut supplements without consulting a healthcare provider first.

Black walnuts are high in omega-3 fatty acids and many vitamins and minerals. They may reduce heart disease risk and possess anticancer and antibacterial properties.

Antioxidants and other plant compounds in black walnut hulls make them a popular herbal supplement — though research is still limited.

Their nutrition profile and bold flavor make black walnuts a beneficial and tasty addition to your diet.