Walnuts (Juglans regia) are a tree nut belonging to the walnut family.

They originated in the Mediterranean region and Central Asia and have been part of the human diet for thousands of years.

These nuts are rich in omega-3 fats and contain higher amounts of antioxidants than most other foods. Eating walnuts may improve brain health and prevent heart disease and cancer ().

Walnuts are most often eaten on their own as a snack but can also be added to salads, pastas, breakfast cereals, soups, and baked goods.

They’re also used to make walnut oil — an expensive culinary oil frequently used in salad dressings.

There are a few edible walnut species. This article is about the common walnut — sometimes referred to as the English or Persian walnut — which is grown worldwide.

Another related species of commercial interest is the eastern black walnut (Juglans nigra), which is native to North America.

Here’s everything you need to know about the common walnut.

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Walnuts are made up of 65% fat and about 15% of protein. They’re low in carbs — most of which consist of fiber.

A 1-ounce (30-gram) serving of walnuts — about 14 halves — provides the following nutrients ():

  • Calories: 185
  • Water: 4%
  • Protein: 4.3 grams
  • Carbs: 3.9 grams
  • Sugar: 0.7 grams
  • Fiber: 1.9 grams
  • Fat: 18.5 grams

Fats

Walnuts contain about 65% fat by weight ().

Like other nuts, most of the calories in walnuts come from fat. This makes them an energy-dense, high-calorie food.

However, even though walnuts are rich in fat and calories, studies indicate that they don’t increase obesity risk when replacing other foods in your diet (, ).

Walnuts are also richer than most other nuts in polyunsaturated fats. The most abundant one is an omega-6 fatty acid called linoleic acid.

They also contain a relatively high percentage of the healthy omega-3 fat alpha-linolenic acid (ALA). This makes up around 8–14% of the total fat content (, , , ).

In fact, walnuts are the only nuts that contain significant amounts of ALA ().

ALA is considered especially beneficial for heart health. It also helps reduce inflammation and improve the composition of blood fats (, ).

What’s more, ALA is a precursor for the long-chain omega-3 fatty acids EPA and DHA, which have been linked to numerous health benefits ().

SUMMARY Walnuts are primarily made up of protein and polyunsaturated fat. They contain a relatively high percentage of omega-3 fat, which has been linked to various health benefits.

Walnuts are an excellent source of several vitamins and minerals, including:

  • Copper. This mineral promotes heart health. It also helps maintain bone, nerve, and immune system function (11, ).
  • Folic acid. Also known as folate or vitamin B9, folic acid has many important biological functions. Folic acid deficiency during pregnancy may cause birth defects (13, ).
  • Phosphorus. About 1% of your body is made up of phosphorus, a mineral that is mainly present in bones. It has numerous functions (15).
  • Vitamin B6. This vitamin may strengthen your immune system and support nerve health. Vitamin B6 deficiency may cause anemia (16).
  • Manganese. This trace mineral is found in the highest amounts in nuts, whole grains, fruits, and vegetables.
  • Vitamin E. Compared to other nuts, walnuts contain high levels of a special form of vitamin E called gamma-tocopherol (, ).
SUMMARY Walnuts are an excellent source of several vitamins and minerals. These include copper, folic acid, phosphorus, vitamin B6, manganese, and vitamin E.

Walnuts contain a complex mixture of bioactive plant compounds.

They’re exceptionally rich in antioxidants, which are concentrated in the brown skin ().

In fact, walnuts ranked second in a study investigating the antioxidant content of 1,113 foods commonly eaten in the United States ().

Some notable plant compounds in walnuts include:

  • Ellagic acid. This antioxidant is found in high amounts in walnuts, along with other related compounds like ellagitannins. Ellagic acid may reduce your risk of heart disease and cancer (, , ).
  • Catechin. Catechin is a flavonoid antioxidant that may have various health benefits, including promoting heart health (, , ).
  • Melatonin. This neurohormone helps regulate your body clock. It’s also a powerful antioxidant that may reduce your risk of heart disease (, 27, ).
  • Phytic acid. Phytic acid, or phytate, is a beneficial antioxidant, though it can reduce the absorption of iron and zinc from the same meal — an effect that's only of concern for those following imbalanced diets ().
SUMMARY Walnuts are one of the richest dietary sources of antioxidants. These include ellagic acid, ellagitannins, catechin, and melatonin.

Walnuts are linked to a number of health benefits. They have been associated with a reduced risk of heart disease and cancer, as well as improved brain function.

Heart health

Heart disease — or cardiovascular disease — is a broad term used for chronic conditions related to the heart and blood vessels.

In many cases, your risk of heart disease can be reduced with healthy lifestyle habits, such as eating nuts (, , ).

Walnuts are no exception. In fact, many studies show that eating walnuts may combat risk factors for heart disease by:

  • lowering LDL (bad) cholesterol (, , , , )
  • reducing inflammation (, )
  • improving blood vessel function, thus cutting the risk of plaque buildup in your arteries (, , )

These effects are likely caused by the beneficial fat composition of walnuts, as well as their rich antioxidant content.

Cancer prevention

Cancer is a group of diseases characterized by abnormal cell growth.

Your risk of developing certain types of cancer can be reduced by eating healthy food, exercising, and avoiding unhealthy lifestyle habits.

Since walnuts are a rich source of beneficial plant compounds, they could be an effective part of a cancer-preventive diet ().

Walnuts contain several bioactive components that may have anticancer properties, including:

  • phytosterols (, )
  • gamma-tocopherol ()
  • omega-3 fatty acids (, , )
  • ellagic acid and related compounds (, )
  • various antioxidant polyphenols ()

Observational studies have linked the regular consumption of nuts to a lower risk of colon and prostate cancer (, ).

This is supported by animal studies indicating that eating walnuts may suppress cancer growth in breast, prostate, colon, and kidney tissue (, , , ).

However, before any solid conclusions can be reached, these effects need to be confirmed by clinical studies in humans.

Brain health

Several studies indicate that eating nuts may improve brain function. They also show that walnuts can help with depression and age-related decline in brain function (, ).

A study in older adults linked regular consumption of walnuts with significant memory improvement ().

Still, these studies were observational and cannot prove that walnuts were the cause of improvements in brain function. Stronger evidence is provided by studies that investigate the effect of eating walnuts directly.

One 8-week study in 64 young, healthy adults, found that eating walnuts improved comprehension. However, significant improvements in non-verbal reasoning, memory, and mood were not detected ().

Walnuts have also been shown to improve brain function in animals. When mice with Alzheimer's disease were fed walnuts every day for 10 months, their memory and learning skills improved significantly ().

Similarly, studies in older rats found that eating walnuts for eight weeks reversed age-related impairments in brain function (, ).

These effects are likely due to the high antioxidant content of walnuts, though their omega-3 fatty acids may play a role as well (, ).

SUMMARY Walnuts are rich in antioxidants and healthy fats. They may reduce heart disease and cancer risk, as well as improve brain function and possibly slow the progression of Alzheimer's disease.

In general, walnuts are considered very healthy, but some people need to avoid them due to allergies.

Walnut allergy

Walnuts are among the eight most allergenic foods ().

Symptoms of a walnut allergy are typically severe and can include allergic shock (anaphylaxis), which can be fatal without treatment.

Individuals with a walnut allergy need to avoid these nuts completely.

Reduced mineral absorption

Like all seeds, walnuts are high in phytic acid ().

Phytic acid, or phytate, is a plant substance that impairs the absorption of minerals — such as iron and zinc — from your digestive tract. This only applies to meals that contain high-phytate foods.

Individuals who follow imbalanced diets rich in phytic acid are at a higher risk of developing mineral deficiencies, but most people shouldn’t need to worry.

SUMMARY Walnuts are very healthy, but some people are allergic and must avoid them. Phytic acid may impair mineral absorption, though this is usually of no concern to people who eat a balanced diet.

Walnuts are rich in heart-healthy fats and high in antioxidants.

What’s more, regularly eating walnuts may improve brain health and reduce your risk of heart disease and cancer.

These nuts are easily incorporated into your diet, as they can be eaten on their own or added to many different foods.

Simply put, eating walnuts may be one of the best things you can do to improve your health.