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 while also helping to prevent heart disease and cancer ().
Walnuts are most often eaten on their own as a snack. However, they can also be added to salads, pastas, breakfast cereals, soups and baked goods.
They are also used to make walnut oil, an expensive culinary oil often used in salad dressings. They are sometimes referred to as common walnuts, English walnuts or Persian walnuts.
Another related species of commercial interest is the eastern black walnut (Juglans nigra), which is native to North America.
The table below contains information on the nutrients in walnuts ():
Walnuts contain about 65% fat by weight ().
Like other nuts, most of the energy (calories) in walnuts comes 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 do not increase the risk of obesity when replacing other foods in the 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 a healthy omega-3 fat called 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 to be especially beneficial for heart health. It also helps reduce inflammation and improve the composition of blood fats (, ).
ALA is also a precursor for the long-chain omega-3 fatty acids EPA and DHA, which have been linked with numerous health benefits ().
Bottom Line: Walnuts are primarily made up of polyunsaturated fat. They contain a relatively high percentage of omega-3 fat, which has been linked with various health benefits.
Vitamins and Minerals
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 (, ).
- Folic acid: Also known as folate or vitamin B9, folic acid has many important biological functions. A folic acid deficiency during pregnancy may cause birth defects (, ).
- Phosphorus: About 1% of our body is made up of phosphorus, a mineral that is mainly present in bones. It has numerous functions in the body ().
- Vitamin B6: This vitamin may strengthen the immune system and support nerve health. A vitamin B6 deficiency may cause anemia ().
- 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 (, ).
Bottom Line: Walnuts are an excellent source of several vitamins and minerals. These include copper, folic acid, phosphorus, vitamin B6, manganese and vitamin E.
Other Plant Compounds
Walnuts contain a complex mixture of bioactive plant compounds.
They are exceptionally rich in antioxidants, which are concentrated in the thin, brown skin ().
In fact, walnuts ranked second in a study investigating the antioxidant content of 1113 foods commonly eaten in the US ().
Some notable plant compounds found 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 the risk of heart disease and help suppress cancer formation (, , ).
- Catechin: Catechin is a flavonoid antioxidant that may have various health benefits. It may also promote heart health (, , ).
- Melatonin: This neurohormone helps regulate the body clock. It is also a powerful antioxidant that may reduce the risk of heart disease (, , ).
- Phytic acid: Also known as phytate, phytic acid may impair the absorption of minerals, such as iron and zinc, from the digestive tract ().
Bottom Line: Walnuts are one of the richest dietary sources of antioxidants. These include ellagic acid, ellagitannins, catechin and melatonin.
Health Benefits of Walnuts
Eating walnuts has been linked to a number of health benefits. These include a reduced risk of heart disease, possible cancer prevention and improved brain function.
Heart disease, or cardiovascular disease, is a broad term used for chronic diseases related to the heart and blood vessels.
In many cases, heart disease may be prevented with healthy lifestyle habits, such as eating nuts (, , ).
Walnuts are no exception. In fact, many studies have shown that eating walnuts may combat risk factors for heart disease by:
- Lowering LDL, the "bad" cholesterol (, , , , ).
- Reducing inflammation (, ).
- Improving the function of blood vessels, cutting the risk of plaque buildup in the arteries (, , ).
These effects are likely caused by the beneficial fat composition of walnuts as well as their rich antioxidant content.
Bottom Line: Walnuts are a rich source of antioxidants and healthy fats. They may also reduce several of the risk factors for heart disease, especially when combined with other healthy lifestyle habits.
Cancer is a group of diseases characterized by abnormal cell growth.
Many forms of cancer can be prevented by eating healthy food, exercising and avoiding unhealthy lifestyle habits.
Since they are a rich source of beneficial plant compounds, walnuts could be an effective part of a cancer-preventive diet ().
Walnuts contain several bioactive components that may have anti-cancer properties. These include:
- Phytosterols (, ).
- Gamma-tocopherol ().
- Omega-3 fatty acids (, , ).
- Ellagic acid and related compounds (, ).
- Various antioxidant polyphenols ().
Observational studies have linked the regular consumption of nuts with a lower risk of colon and prostate cancer (, ).
This is supported by animal studies indicating that eating walnuts may suppress cancer growth in the breasts, prostate, colon and kidneys (, , , ).
However, before any stronger claims can be made, these effects need to be confirmed by clinical studies in humans.
Bottom Line: Walnut consumption may lower the risk of certain types of cancer. However, further studies are needed before any solid conclusions can be reached.
Several human 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 of elderly people linked regular consumption of walnuts with significant memory improvement ().
However, these studies were observational and therefore can't 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 of 64 young, healthy adults, found that eating walnuts improved comprehension. However, significant improvements in non-verbal reasoning, memory and mood were not detected ().
Nevertheless, walnuts have also been shown to improve brain function in animals.
In another study, mice with Alzheimer's disease were fed walnuts every day for 10 months. Their memory and learning skills improved significantly ().
Similarly, studies of elderly rats found that eating walnuts for eight weeks reversed age-related impairments in brain function (, ).
These effects are probably due to the high antioxidant content of walnuts. However, their omega-3 fatty acids may also play a role (, ).
Bottom Line: A walnut-rich diet may improve brain function and possibly slow the progression of Alzheimer's disease. However, the evidence is limited and further human studies are needed.
Adverse Effects and Individual Concerns
In general, walnuts are very healthy. However, some people may be allergic to them.
Walnuts can also reduce mineral absorption in certain individuals.
Walnuts are among the eight most allergenic foods ().
Additionally, the symptoms of a walnut allergy are typically severe. Walnuts sometimes cause an 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 the digestive tract. This only applies to meals that contain high-phytate foods.
Individuals that follow diets rich in phytic acid but low in iron and zinc may be at a higher risk of developing mineral deficiencies.
Bottom Line: Walnuts are exceptionally healthy. However, some people may be very allergic to them. Walnuts may also reduce mineral absorption in some individuals.
Walnuts are rich in heart-healthy fats and high in antioxidants.
Additionally, regular consumption of walnuts may improve brain health and help prevent heart disease and cancer.
These nuts are easily incorporated into the diet, since they can be eaten on their own or added to many different foods.
Simply put, eating walnuts may be one of the easiest things you can do to improve your health.