Let’s Think on It: Walnuts and Alzheimer’s Disease Progression

Research has shown that a healthy diet may contribute to good brain health and overall well-being. Studies reveal that walnuts can be part of dietary patterns that could play a beneficial role in cognitive function and neurodegenerative conditions like Alzheimer’s disease.¹

Ongoing research has found evidence that eating certain foods, like walnuts, may be linked with:¹

• improved cognitive function and memory in groups at high risk for age-related cognitive impairment
• a reduced risk of other diseases, such as cardiovascular disease or type 2 diabetes, which are risk factors for the development of dementia
• a reduced risk of developing, or delaying the onset and/or slowing the progression of Alzheimer’s disease (AD)

These findings warrant additional research in order to clearly understand the role that diet quality, nutrient intake, and the consumption of specific foods, like walnuts, may play in supporting potential benefits to cognitive function and reduction in risk for other diseases.

Emerging research from pre-clinical^*,+ and human studies^{^} suggests that eating about 1–2 ounces of walnuts (about a handful) per day seems to show the strongest potential benefits for brain health.¹ While the research resulted in positive findings, it was performed in cells and therefore findings cannot yet be correlated to humans. It is important for additional research to be done to fully understand the implications for humans.

In conditions like Alzheimer’s disease, signs and symptoms may not show until much later in life. So, adopting simple and nourishing habits early in life and doing them often, like eating walnuts, could be a promising action that may benefit cognitive function and neurodegenerative conditions.¹

Read on to learn more about each of these types of studies and their findings

Humans^{^}

• Clinical studies in humans show eating walnuts reduced oxidative stress, inflammation, and other risk factors for AD.¹ Also, researchers have identified positive associations between walnut intake and cognitive function within a wide array of populations, including older adults who may be at higher risk for developing neuro-degenerative conditions.^1-5,6-9
• But, we don’t eat walnuts by themselves all the time. We eat them as part of complex diets, like the Mediterranean diet. Clinical and observational studies show that following the Mediterranean diet seems to be linked with age-related neuroprotection and possibly less risk of AD progression.^{6-8, 10-12} Walnuts are a staple nut and important component of the Mediterranean diet.
• Brain glucose hypometabolism is widely regarded as a marker of neurodegeneration. A cross-sectional study of 320 people, at increased risk for AD but without cognitive impairment, in the ALzheimer’s and FAmilies+ (ALFA) cohort in Spain were analyzed to determine the impact of omega-3 rich foods on brain glucose metabolism, a preclinical feature of AD. Results showed that those with higher blood levels of omega-3 alpha-linolenic acid (ALA), which comes from vegetable sources such as walnuts, showed a better use of brain glucose in those at-risk brain areas. This was especially prominent in participants with a higher genetic risk of Alzheimer’s (i.e., APOE ε4 load). Conversely, omega-3 docosahexaenoic (DHA), coming from marine sources, were more beneficial in those who, despite not presenting symptoms of Alzheimer’s, were already beginning to have the accumulation of proteins (amyloid and tau) that are characteristic of the disease.⁹ Additional research is needed to extrapolate these results to other populations and to understand the effect of walnuts alone on dietary ALA levels and brain glucose metabolism.

^{^}Further work is needed to improve our understanding of the complex pathways through which eating patterns that include walnuts can influence the brain or affect risk of or progression of neurodegenerative conditions. Observational studies cannot prove cause and effect. Findings in clinical studies are limited to the population who received the walnut intervention and cannot be extrapolated broadly to other groups. More observational studies and clinical trials are needed to determine the optimal quantity of walnuts needed to contribute to brain health and/or affect progression of neurodegenerative conditions.

Animals⁺

• A 2018 study using a mouse model of early AD published in the Journal of Alzheimer’s Disease found that eating walnuts (equivalent to 1 oz. and 1.5 oz. of walnuts per day in humans) may reduce the risk or delay the onset and progression of AD by reducing oxidative stress and inflammation.¹⁰
• These findings add to evidence from a 2014 animal study which found that a diet including walnuts may play a role in AD by impacting learning skills, memory, anxiety and motor development.¹¹

⁺Animal studies are valuable for providing background information and can be used as a basis for additional research needed to determine the effects on humans. Results from studies done in animals cannot be applied to humans.

Cell^*

Walnut oil has been found to protect brain cells when using an early model of AD.^{12, 13}

• Researchers specifically published a new 2022 study in the journal Nutrients¹² where they exposed human brain cells in an isolated condition to roughly 10 micrograms/mL of walnut oil from 5 grams of California walnut powder that contained various fatty acid compounds including the plant-based omega-3 alpha-linolenic acid.
• The study found that walnut oil protected cells from oxidative stress, enhanced brain cell function, and reduced the formation of markers of AD progression known as beta-amyloid. The observed effects of walnut oil on the exposed human brain cells should be understood as preliminary and additional future investigations are needed.

^*Cell studies are valuable for providing background information and can be used as a basis for additional research needed to determine the effects on humans. Results from studies done in cells cannot be applied to humans.

What does it all mean?

Additional research is underway, however, walnuts appear to have a unique combination of nutrients that may work together to deliver beneficial effects in the context of neurodegenerative diseases.¹ Specifically, walnuts provide plant-based nutrients with anti-inflammatory and antioxidant properties in a 1 oz. serving.^1,14,~ including:

• excellent source of the plant-based omega-3 alpha-linolenic acid (2.5 g/o.z)
• polyphenols (69.3 ± 16.5 μmol catechin equivalents/g)
• tocopherols [major forms of vitamin E] (5.91 mg/oz.)
• melatonin (45 mg/oz.)
• folate (30 mcg DFE/oz.)
• selenium (1 mcg/oz.)

Recent research demonstrates that including a daily serving of walnuts (about a handful) may have a beneficial effect on brain health with other potential positive whole-body effects. Walnuts can easily be incorporated into all styles of recipes whether savory, sweet, a lunch, or a snack! For a new recipe try the Strawberry, Cucumber & Pearl Couscous Salad or these Walnut Chocolate Bliss Balls.
To continue learning more about how walnuts play a role in healthy aging and brain health, check out this article.

~Supportive but not conclusive research shows that eating 1.5 ounces of walnuts per day, as part of a low saturated fat and low cholesterol diet and not resulting in increased caloric intake, may reduce the risk of coronary heart disease. (FDA) One ounce of walnuts offers 18 grams of total fat, 2.5 grams of monounsaturated fat, 13 grams of polyunsaturated fat including 2.5 grams of alpha-linolenic acid – the plant-based omega-3.

References:

1. Chauhan A, Chauhan V. Beneficial effects of walnuts on cognition and brain health. Nutrients. 2020;12(2):550.

2. Theodore LE, Kellow NJ, McNeil EA, Close EO, Coad EG, Cardoso BR. Nut consumption for cognitive performance: A Systematic review. Adv Nutr. 2021;12(3):777-792.

3. Arab L, Ang A. A cross sectional study of the association between walnut consumption and cognitive function among adult US populations represented in NHANES. J Nutr Health Aging. 2015;19(3):284-290.

4. Pribis P, Shukitt-Hale B. Cognition: the new frontier for nuts and berries. Am J Clin Nutr. 2014;100 Suppl 1:347S-52S.

5. Sala-Vila A, 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;111:590–600.

6. Valls-Pedret C, Sala-Vila A, Serra-Mir M, et al. Mediterranean diet and age-related cognitive decline: A randomized clinical trial [published correction appears in JAMA Intern Med. 2018 Dec 1;178(12):1731-1732]. JAMA Intern Med. 2015;175(7):1094-1103.

7. Barbaresko J, Lellmann AW, Schmidt A, et al. Dietary factors and neurodegenerative disorders: An umbrella review of meta-analyses of prospective studies. Adv Nutr. 2020;11(5):1161-1173.

8. Gutierrez L,et al. Effects of nutrition on cognitive function in adults with or without cognitive impairment: A systematic review of randomized controlled clinical trials. Nutrients. 2021;13:3728.

9. Lazaro, I, Grau-Rivera O, Suarez-Calvet M, et al. Omega-3 blood biomarkers relate to brain glucose uptake in individuals at risk of Alzheimer’s dementia. Alzheimer’s Dement. 2024;16:e12596.

10. Pandareesh MD, Chauhan V, Chauhan A. Walnut Supplementation in the diet reduces oxidative damage and improves antioxidant status in transgenic mouse model of Alzheimer’s disease. J Alzheimers Dis. 2018;64(4):1295-1305.

11. Muthaiyah B, Essa MM, Lee M, Chauhan V, Kaur K, Chauhan A. Dietary supplementation of walnuts improves memory deficits and learning skills in transgenic mouse model of Alzheimer’s disease. J Alzheimers Dis. 2014;42(4):1397-1405.

12. Esselun C, Dieter F, Sus N, Frank J, Eckert GP. Walnut oil reduces Aβ levels and increases neurite length in a cellular model of early Alzheimer disease. Nutrients. 2022;14(9):1694.

13. Muthaiyah B, Essa MM, Chauhan V, Chauhan A. Protective effects of walnut extract against amyloid beta peptide-induced cell death and oxidative stress in PC12 cells. Neurochem Res. 2011;36(11):2096-2103.

14. U.S. Department of Agriculture, Agricultural Research Service. FoodData Central, 2019. fdc.nal.usda.gov.