Walnuts are recognized as a nut with a high content of alpha-linolenic acid (ALA), a plant-based omega-3 fatty acid. A single handful (about 28g), which is equivalent to 12 to 14 walnut halves, contains about 2.5g of alpha-linolenic acid. In addition to alpha-linolenic acid, they also contain arginine (an amino acid), polyphenols (antioxidants), and magnesium (a mineral). Because a single handful contains a not-so-insignificant 185 kcal, it is best to control your portion size when eating them. Based on the results of various studies, let's look at 5 health benefits of walnuts.

Reduction of LDL Cholesterol

Walnuts are rich in polyunsaturated fatty acids—such as omega-3 and omega-6 (fatty acids with multiple double bonds)—which can help lower LDL cholesterol levels. A meta-analysis published in 2018 in the international journal American Journal of Clinical Nutrition analyzed 26 clinical trials (involving 1,059 participants) comparing diets supplemented with walnuts to regular diets.

As a result, the group following the walnut diet showed a greater reduction in LDL cholesterol by 5.51 ㎎/㎗ (3.73%) and total cholesterol by 6.99 ㎎/㎗ compared to the control group. Improvements in cholesterol were observed even when consuming less than 28g per day, with no adverse effects on body weight or blood pressure.

Increase in Beneficial Gut Bacteria

The dietary fiber and polyphenols in walnuts serve as food for gut microbes and can alter the gut environment. In a study published in 2018 in the international journal The Journal of Nutrition, 18 healthy adults (average age 53.1) ate 42g of walnuts daily for 3 weeks. As a result, beneficial bacteria that produce substances nourishing the gut mucosal lining increased, while bile metabolites that can irritate the gut mucosa and induce inflammation decreased by 25 to 45%. Additionally, LDL cholesterol dropped by 7%.

Nutritionist Amber Sommer explained via Cleveland Clinic's Health Essentials, "Gut microbes are involved in inflammation, digestion, and immune function, and can also affect mental health," adding, "Walnuts are also helpful in improving the gut microbial environment."

Improvement of Vascular Function

Alpha-linolenic acid helps reduce inflammation in the inner walls of blood vessels, while arginine serves as a raw material for nitric oxide, a substance that widens blood vessels. A study published in 2012 in the international journal Journal of the American College of Nutrition compared 46 overweight adults with abdominal obesity (average age 57.4) over two 8-week periods—one when eating walnuts and one when not.

During the period when they consumed 56g of walnuts daily, their vasodilation capacity improved by 1.4%, which was a greater improvement margin than during the period without walnuts (0.3%). However, the 56g of walnuts consumed in this study is twice the amount of a single handful (about 28g) and amounts to 366 kcal. To avoid excess calorie intake, it is better to replace snacks like cookies with walnuts rather than simply adding them to your usual diet.

Enhancement of Cognitive Function

The alpha-linolenic acid, polyphenols, and vitamin E in walnuts are involved in preventing brain cell damage and inflammation. A study published in 2015 in the international journal The Journal of Nutrition, Health & Aging analyzed the relationship between walnut consumption and cognitive function in adults aged 20 to 90 based on data from the National Health and Nutrition Examination Survey (NHANES). The results showed that among those aged 60 and older, individuals who consumed an average of 13.1g of walnuts per day scored 7.1 points higher on memory tests and 7.3 points higher on information processing speed tests (based on percentiles) than those who did not.

However, because this study was a cross-sectional study comparing walnut intake and test scores at a specific point in time, it cannot be definitively concluded that walnut consumption enhanced cognitive function. A 2020 study published in the international journal Public Health Nutrition involving 3,632 Americans aged 65 and older also found that walnut consumers had higher cognitive scores, but there was no difference in the rate of cognitive decline with age. In other words, while an association between walnut intake and cognitive function is confirmed, the evidence is not yet sufficient to establish causality.

Suppression of Weight Gain

Walnuts can help maintain a feeling of fullness for a longer time due to their protein, dietary fiber, and unsaturated fats. A cohort study published in 2019 in the international journal BMJ Nutrition, Prevention & Health tracked approximately 145,000 healthy US adults for over 20 years. The results showed that individuals who increased their daily walnut intake by half a handful (14g) had a 15% lower risk of obesity, and their weight gain accumulated every 4 years was about 0.37 kg less.

Nutritionist Sommer advised, "Like other nuts, walnuts are high in calories, so if weight is a concern, you need to watch your intake," adding, "A daily handful or eating them a few times a week is appropriate."

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