Walnuts are packed with essential macro- and micronutrients. One ounce of walnuts (about 14 halves) provides 4.3g of protein, 1.9g of fiber, 13.4g of polyunsaturated fatty acids (including 10.8g of linoleic acid and 2.6g of alpha-linolenic acid [ALA]), 98.1mg of phosphorous, 44.8mg of magnesium, 0.97mg of manganese, 0.45mg of copper, and 27.8µg of folate.¹ Compared to other tree nuts, walnuts contain the most plant-based polyunsaturated fatty acids and are the best source of ALA, an omega-3 fatty acid.² Walnuts are also a good source of polyphenols.^2,3 ALA exerts anti-inflammatory effects,^2,3 and polyphenols have demonstrated anti-inflammatory, antibacterial, and anticarcinogenic activity.² In the two-year Walnuts and Healthy Aging (WAHA) study, adding 30 to 60g of walnuts per day to the diet of older individuals (aged 63–79 years) was associated with significantly higher intake of total polyphenols, flavonoids, flavanols, and phenolic acids, compared to controls with no walnut intake.⁴ 

Health Benefits

Cardiovascular and metabolic health. Various studies have shown an association between walnut intake and reduced total cholesterol, low-density lipoprotein (LDL) cholesterol, and triglycerides, but no association between walnut intake and high-density lipoprotein (HDL) concentration.^5,6 However, findings from the WAHA study showed that triglyceride levels were significantly reduced in both the walnut-enriched diet and control groups,⁷ and a 2022 review that found a significant association between walnut intake and decreased total cholesterol and LDL cholesterol noted significant between-study heterogeneity and results that might have been prone to bias;⁵ thus, the link between walnuts and cholesterol and triglycerides needs to be evaluated further. 

Research is mixed on the impact of walnuts on blood pressure, with some studies indicating that adding walnuts to the diet does not significantly affect blood pressure, although evidence from the WAHA study suggests that walnut consumption might improve blood pressure in older adults.^7,8

Walnuts might reduce the risk of Type 2 diabetes, although they do not appear to be beneficial for glycemic control.⁸ In addition, walnut consumption is not associated with metabolic syndrome.^7,8 

Cognition.Adding walnuts to the diet might positively impact cognition. Research has shown that among adults, consuming nuts, particularly walnuts, was associated with superior cognition scores, compared to no nut intake. Compared to a low-fat diet, a walnut-enriched diet was associated with improved cognitive function among healthy adults. Additionally, an eight-week trial showed a connection between walnut consumption and improved verbal reasoning in young adults.³ However, more extensive research is required before conclusive statements can be made about the effect of walnut consumption on cognition.

Walnuts could potentially protect against age-related cognitive decline, mild cognitive impairment, and Alzheimer’s disease through various mechanisms (e.g, reducing oxidative stress and inflammation).³ However, the WAHA study showed no effect of walnut consumption on delaying cognitive decline among healthy, older adults.⁹ Thus, more research in this area is needed.

Sources

1. US Department of Agriculture. Nuts, walnuts, English. https://fdc.nal.usda.gov/fdc-app.html#/food-details/170187/nutrients. Accessed 26 Mar 2024.
2. Fan N, Fusco JL, Rosenberg DW. Antioxidant and Anti-inflammatory properties of walnut constituents: focus on personalized cancer prevention and the microbiome. Antioxidants (Basel). 2023;12(5):982. 
3. Chauhan A, Chauhan V. Beneficial effects of walnuts on cognition and brain health. Nutrients. 2020;12(2):550. 
4. Amen RI, Sirirat R, Oda K, et al. Effect of walnut supplementation on dietary polyphenol intake and urinary polyphenol excretion in the Walnuts and Healthy Aging study. Nutrients. 2023;15(5):1253.
5. Alshahrani SM, Mashat RM, Almutairi D, et al. The effect of walnut intake on lipids: a systematic review and meta-analysis of randomized controlled trials. Nutrients. 2022;14(21):4460.
6. Guasch-Ferré M, Li J, Hu FB, et al Effects of walnut consumption on blood lipids and other cardiovascular risk factors: an updated meta-analysis and systematic review of controlled trials. Am J Clin Nutr. 2018;108(1):174–187.
7. Al Abdrabalnabi A, Rajaram S, Bitok E, et al. Effects of supplementing the usual diet with a daily dose of walnuts for two years on metabolic syndrome and its components in an elderly cohort. Nutrients. 2020;12(2):451. 
8. Ros E, Singh A, O’Keefe JH. Nuts: natural pleiotropic nutraceuticals. Nutrients. 2021;13(9):3269. 
9. Sala-Vila A, Valls-Pedret C, Rajaram S, et al. Effect of a 2-year diet intervention with walnuts on cognitive decline. The Walnuts and Healthy Aging (WAHA) study: a randomized controlled trial. Am J Clin Nutr. 2020;111(3):590–600.