Juglans regia (Walnut): Health benefits and side effects 

Know in one minute about Juglans regia (Walnut)

  • Rich sources of alpha-linolenic acid (Omega 3 PUFA), melatonin, and antioxidants.
  • Reduce high blood pressure problems and prevent blood clotting.
  • Improve memory, boost brain activity, and treat Alzheimer’s disease.
  • Enhance metabolism, treat obesity, diabetes, fatigue, depression, and anxiety.
  • Induce sleep, lower cholesterol levels, and prevent the risk of heart disease.
  • Good for pregnant women, children, young as well as older people

Introduction

Walnut (Juglans regia L.; Family Juglandaceae) is an important temperate nut crop. It is a rich source of proteins, fats, minerals, and is a concentrated source of energy. After blackberries, walnuts ranked second for their antioxidant activities. Juglans regia (walnut) is unique because they have a perfect balance of n-6 and n-3 polyunsaturated fatty acids (4:1) (1).

It can be consumed in various forms such as raw, unprocessed, or roasted, salted, and flavored. Due to its pleasant taste, it is used as a flavor enhancer in yogurt, pizza, and cake. It is also used on salad, dessert, ice-creams, candy, and biscuits. 

Geographical distribution

Juglans regia (walnut) is growing in many parts of the world, including Asia (foothills of the Himalayas, Iran, China, and Japan), Europe, North and South America, South Africa, Australia, and New-Zealand. 

Botanical description

It is a large tree with a height of about 20–30 m. The bark is gray, smooth on young trees, and fissuring with age. The leaves are alternate, pinnate (20–45 cm long) and give off a lemon /lime scent when crushed. The male and female flowers appeared on them separately. Pollination is carried out by the wind.

Common name

The common walnut, English walnut, Persian walnut, White walnut, Carpathian walnut, and Madeira nut

Major constitutes of Juglans regia (walnut)

The whole walnut tree including the seeds, leaves, husks, nuts, and kernels are rich in active phytochemicals and natural antioxidants, which have been proven to ameliorate/prevent many diseases including cardiovascular disease, diabetes, obesity, cancer, neurological diseases, etc.

1. Alpha-linolenic acid in Juglans regia (walnut) 

Walnut (56 g/per day) contains alpha-linolenic acid that is metabolized into bioactive oxylipins which are helping to reduce inflammation.

Thus alpha-linolenic that improves the composition of blood fats prevents blood clotting and keeps heart as well as brain health (2).

2. Phytosterols in walnut

The phytosterols help to reduce low-density lipoprotein (LDL)-cholesterol levels. 

3. Various minerals in walnut

It contains little sodium but a good amount of potassium, magnesium, and calcium. These minerals control blood pressure, prevent stroke, and reduce heart-related problems. It also helps to maintain bone, nerve, and immune system function. 

4. Vitamins

Vitamin E is made up of four tocopherols such as α-tocopherol, β-tocopherol, γ-tocopherol, and δ-tocopherol. Walnut contains a high amount of γ-tocopherol which removes harmful radicals from the body and reduces inflammation.

It also contains vitamin B6, vitamin B9 that may strengthen the immune system, support nerve health, and reduce the risk of anemia.

5. Melatonin

Melatonin is a hormone that regulates the sleep-wake cycle, helps to fall asleep by calming the body before bed. Walnut contains a good amount of phytomelatonin which improve sleep quality

6. Protein

Proteins (lysine/arginine) found in walnuts help to widen the blood vessel thus inhibit blood clotting.

7. Polyphenols

Walnut contains ellagitannins and ellagic acid that reduce the risk of heart disease and help to suppress cancer formation. It is also effective for the reduction of fat, LDL-cholesterol, and glucose levels (3)

Nutritional value of Walnut

According to USDA tamarind contains very good amounts of oil (52–70%) (4). In addition, oil also contains considerable amounts of proteins (up to 24% of the walnut seed weight), carbohydrates (12–16%), fiber (1.5–2%), and minerals (1.7–2%) (5).

Compound Amounts per 100 g.
Water  4.07 g
Energy  654 Kcal
Protein  15.23 g
Total lipid (fat)  65.21 g
Carbohydrate 13.71 g
Fiber, total dietary  6.7 g
Sugar 2.61 g
Calcium 98 mg
Iron, Fe  2.91 mg
Magnesium  158 mg
Phosphorus  346 mg
Potassium  441 mg
Sodium   2 mg
Zinc  3.09 mg
Copper  1.58 mg
Manganese 3.41 mg
Selenium 4.9 µg
Vitamin C 1.3 mg
Thiamin  0.43 mg
Riboflavin 0.15 mg
Niacin 1.12 mg
Pantothenic acid 0.57 mg
Vitamin B-6 0.537 mg
Folate 98 µg
Vitamin A, RAE 1 µg
Vitamin A, IU 20 IU
Vitamin K  0 µg
Fatty acids, total saturated  6.12 g
Fatty acids, total monounsaturated  8.93 g
Fatty acids, total polyunsaturated  47.17 g

Health benefits of Juglans regia (walnut)

1. Improve gut microbiota

Intake of walnuts (43 g/per day) for 8 weeks is effective to enhance the healthy bacteria which live in the gut (6).  These bacteria promote gastrointestinal health and reduce the risk of various diseases (7).

2. Keep the heart-healthy

Daily intake of walnuts decreases low-density lipoprotein (LDL) cholesterol, blood pressure, oxidative stress, and inflammation (8). Thus prevent hypertension and reduce the risk of cardiovascular disease like stroke (9).

3. Reduce Obesity

Walnut contains a rich amount of protein and dietary fiber, which increases fullness and decreases fat absorption (10). Thus regular consumption (approximately one handful daily or 28–56 g of nuts for a long time helps to prevent obesity  (11).

4. Treat diabetes

Intake of walnut helps to reduce the blood sugar level. Thus higher walnut consumption is associated with a lower risk of type 2 diabetes in women (12).

5. Boost brain activity

Daily walnut consumption is effective to increase serotonin levels in the brain of normal and pregnant women. This serotonin is a chemical that helps to convey signals from one area of the brain to another (13). Thus walnut fatty acids and vitamin E help to improve the learning and memory of the person and their children (14).

6. Good for Older people

Daily consumption of walnut (43 g/per day or 281 kcal) increases energy, protein, vegetable protein, omega fatty acids, polyphenols, and tocopherols (15). It also inhibits the accumulation of damaged protein, inflammation in the brain, and improves interneuronal signaling of the aged person (16).

Thus walnut diet not only gives important nutrients but also reduces the risk of Alzheimer’s disease and hypertension (17).

7. Treat fatigue

Ingestion of walnut (oligopeptides) helps to improve energy metabolism, reduce oxidative stress, cell damage, and muscular injury.  Thus keep you active and treat tiredness (18).

8. Antimicrobial properties

Walnut ingestion help to fight against different multidrug-resistant bacteria such as Staphylococcus aureus and Escherichia coli (19).

9. Antioxidant properties

Walnut contains fat, protein, vitamins, and minerals along with phenolic compounds (ellagitannin) which help to remove harmful radicals from the body and fight against various diseases (20, 21).

10. Good for oral hygiene

Walnut bark inhibits the growth of Staphylococcus aureus, Streptococcus mutans, Escherichia coli, Pseudomonas aeruginosa, and yeast Candida albicans.

It also helps to increase the pH of saliva, reduce the incidence of gingival and periodontal infections.  Thus brushing the teeth with this bark may improve oral hygiene, prevent plaque and caries formation (22).

11. Reduce depression and improve mood

Walnut is an excellent source of omega 3 polyunsaturated fatty acids (PUFA), Vitamin E, polyphenol, and melatonin. These compounds help to improve mood, reduce feelings of anger, anxiety, fear, depression, and confusion (23).

12. Anticancer properties

walnuts contain polyphenols, quinones, proteins, juglone, and essential fatty acids that inhibit the growth of cancer cells, induce apoptosis, and inhibit metastasis (24).

Thus walnuts show anticancer activity against breast, colon, lung, prostate, and skin cancer cells. (25)

Side effect of walnut 

A research study suggested that the intake of walnuts even in high dosage does not cause any harmful effects on the body. Besides, it may improve kidney structure and function and help in the treatment of some chronic diseases. (26) However other studies reported some side effects of walnuts

1. Risk of contact dermatitis

The unripe green walnut husk is containing juglone which may cause irritant reactions and skin hyperpigmentation. However, this compound amount decreases during maturation but precaution should be needed (27).

2. Skin rash and diabetic should avoid excess

Ingestion of 250 ml of Walnut hydrosol after meals twice a day for four weeks helps to reduce blood sugar. However, it also may cause some side effects such as skin rash and hypoglycemic coma. Thus walnut should not be advised extensively to people with diabetes (28).

Q&A

How many walnuts should you eat in a day?

Normally it depends on the person’s condition like age and health problems. However, according to the Food and Drug Association (FDA) 1.5 ounces (42 g or 4-5) walnuts are recommended in the daily diet (29). Moreover, if you are trying to lose weight, take 30 g. walnuts/day (30).

Are walnuts good for the brain?

Walnut is a very healthy fruit; it is good for brain development as well as its activity. It increases serotonin levels and enhances signals in the brain when consumed from childhood with 20 – 30 g per day. The antioxidants in 30 g walnuts are more than the antioxidants that a normal man gets from the fruit and vegetable he eats all day long (31).

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