The body of evidence about nuts and brain health continues to grow, with new local and international research papers regularly published.

Key studies: systematic literature reviews and meta-analyses

Impact of nut consumption on cognition across the lifespan. (Nishi et al, 2023)
This narrative review outlines the epidemiological, clinical trial, and mechanistic evidence of the effect of exposure to nuts on cognitive performance. It found that the available evidence suggests a possible role for nuts in the maintenance of cognitive health and prevention of cognitive decline across the lifespan, particularly in older adults and those at higher risk. Walnuts, as a rich source of the plant-based polyunsaturated omega-3 fatty acid alpha-linolenic acid, are the nut type most promising for cognitive health. The authors conclude that future studies are needed in this area.

Does the evidence support a relationship between higher levels of nut consumption, lower risk of depression, and better mood state in the general population? A systematic review. (Fernandez-Rodriguez et al, 2022).
This systematic review, of 10 previously-published studies, involved more than 66,000 people, across five countries. Six studies looked at nut consumption and depression, and four focussed on nuts and mood state. The researchers concluded: “Higher nut consumption is associated with a reduced risk of depression and better mood state in the general population”. They acknowledge that further studies, with larger sample sizes and longer follow-up periods, will add to knowledge in this area.

Nut consumption for cognitive performance: A systematic review. (Theodore et al, 2020).
This review looked at the link between nut intake and cognitive performance. Twenty-two studies, involving 43,793 adults, were included in the review. The researchers found a lack of consistency across the studies when it came to study design, the types of nut used, and the cognitive outcomes measured. As a result, they concluded that, to date, the evidence is inconsistent when it comes to nut consumption having a protective effect on cognition. They found that studies targeting populations with a higher risk of cognitive decline tended to have a more favourable outcome.

Nut consumption and cognitive function: A systematic review. (Arias-Fernandez et al, 2019)
Systematic review finds daily nut consumption in the context of a healthy diet has positive effects on the cognitive function in adults.

Diet and the risk of unipolar depression in adults: A systematic review of cohort studies. (Sanhueza et al, 2013)
A diet rich in folate, omega-3 fatty acids, olive oil, fish, fruits, vegetables and nuts may have a protective effect against depression, although the evidence is currently insufficient to establish an independent protective role for nuts alone.

Other evidence

Adherence to a Mediterranean diet is inversely associated with anxiety and stress but not depression: A cross-sectional analysis of community-dwelling older Australians. (Allcock et al, 2024).
This cross-sectional analysis of 294 older Australians (≥ 60 years) showed that adherence to a Mediterranean diet (MD) was inversely associated with severity of symptoms related to anxiety and stress. However, adherence to a MD was not related to depressive symptoms. In addition, it found that certain individual dietary components within a MD, including fruit, nuts, legumes, and a low consumption of sugar-sweetened beverages (<250mL per day), were inversely associated with the severity of symptoms related to anxiety and stress.

Recent advances on the effect of nut consumption on cognitive improvement. (Wu et al, 2023).
This review article summarises the effect of nut consumption on oxidative stress, inflammation, and the gut microbiota, which all impact cognitive function. It outlines findings from observational studies, suggesting nut consumption is linked with a lower incidence of cognitive disorders. The researchers also outline the potential biological mechanisms behind this, including the synergistic action between all nut constituents, such as unsaturated fatty acids, bioactive peptides, and polyphenols. They say that further large-scale clinical trials are still required in this area.

Higher versus lower nut consumption and changes in cognitive performance over two years in a population at risk of cognitive decline: A cohort study. (Ni et al, 2023).
This prospective cohort study, involving 6,630 participants aged 55-75 years with overweight/obesity and metabolic syndrome (placing them at risk of cognitive decline), found frequent nut consumption was linked with smaller decline in general cognitive performance over a 2-year period. It suggests a potential dose-response relationship between nut consumption and a delay in cognitive decline. Randomised clinical trials are needed in this area to verify the findings.

Longer-term mixed nut consumption improves brain vascular function and memory: A randomized, controlled crossover trial in older adults. (Nijssen et al, 2023).
This randomised, single-blinded, cross-over trial consisted of 28 healthy participants, with a mean age of 65 years +/- 3 years. The intervention (60g/day of mixed nuts) and control periods (no nuts) were both across 16 weeks, and separated by an 8-week washout period. After nut consumption, cerebral blood flow, a marker of brain vascular function, was higher in certain regions of the brain. Nut consumption also improved endothelial function, and benefitted arterial stiffness and retinal microvasculature. Some aspects of cognitive performance (visuospatial memory, and verbal memory) also improved.

Nut consumption and depression: Cross-sectional and longitudinal analyses in two cohorts of older adults. (Fernández-Rodríguez et al, 2023).
This observational research, investigating two cohorts of older Spanish adults (≥65 years), found nut consumption to be linked with a lower risk of depression. In the meta-analysis of cross-sectional results from the two studies, compared to consuming <1 serving (30g) of nuts/week, the odds ratio for depression was 0.90 (0.64, 1.16) for consuming 1 to <3 servings/week and 0.92 (0.70, 1.13) for consuming ≥3 servings/week. The corresponding figures for the longitudinal results were 0.90 (0.41, 1.38) and 0.66 (0.35, 0.97).

Nut consumption is associated with a lower risk of depression in adults: A prospective analysis with data from the UK Biobank cohort. (Bizzozero-Peroni et al, 2023).
This study analysed whether nut consumption is linked with the risk of depression. It involved 13,504 middle-aged and older UK-based adults, without depression at baseline, who were tracked over an average of 5.3 years – by which time 1,122 (8.3%) cases of depression were identified. Compared with no nut consumption, the daily consumption of >0 to 1 serve of 30g of nuts/day was linked with a 17% lower risk of depression, regardless of all potential confounders considered.

Mid-life adherence to the Dietary Approaches to Stop Hypertension (DASH) diet and late-life subjective cognitive complaints in women. (Song et al, 2023).
This prospective cohort study found greater adherence to the DASH diet in mid-life was associated with ~20% lower odds of having ≥2 subjective cognitive complaints (a predictor for neurocognitive disorders) in later life. It involved 5,116 US-based women, with a mean age at baseline of 46.3 years – followed over an average (mean) of 32.6 years. A higher ‘DASH score’ was based on adherence to a dietary pattern defined by low intakes of red meat, sodium, sweets, and high intakes of fruits (including fruit juices), vegetables (excluding potatoes), legumes and nuts, low-fat dairy, and grains.

Mixed tree nuts, cognition and gut microbiota: A 4-week, placebo-controlled, randomized crossover trial in healthy non-elderly adults. (Haskell-Ramsay et al, 2022).
The study, over four weeks, looked at the effects of consuming 30g/day mixed tree nuts, versus placebo, on cognition and mood in 79 healthy adults (18-49 years). It also investigated changes to gut microbial species and the potential for these to impact cognition. It found that nut consumption led to significant improvements to accuracy and speed of response, and enriched a microbial taxa associated with gut health. But the effects appeared to be independent of one another.

Beneficial effects of nut consumption on cognitive function among elderly: Findings from a 6-year cohort study. (Li et al, 2022).
This research found higher nut consumption to be related to a lower risk of cognitive impairment in Chinese elderly. It involved 9,028 study participants from the Zhejiang Ageing and Health Cohort, whose cognitive function was assessed at baseline and three more times, over a six-year period. Participants consuming ≥70g of nuts per week had a 17% lower risk of cognitive impairment, compared with non-consumers or those who ate nuts less than weekly.

Nut consumption and academic performance among adolescents: the EHDLA study. (López-Gil et al, 2022).
A cross-sectional study, involving 846 Spanish adolescents (aged 12-17 years), looked at academic performance data from school records, and used a food frequency questionnaire to estimate nut consumption. Compared to no consumption, ≥ 3 nut servings (with a serving classed as 20-30g nuts) per week was consistently associated with higher academic performance. The researchers note that these cross-sectional results should be confirmed in longitudinal and intervention studies.

Association of dietary patterns with cognitive function and cognitive decline in Sydney Memory and Ageing Study: A longitudinal analysis. (Chen et al, 2021).
This study analysed data, on 1,037 adults aged 70-90 years at baseline, as part of the Sydney Memory and Ageing study. Mediterranean diet and Dietary Approaches to Stop Hypertension (DASH) diet scores were generated based on dietary intake for each individual. Neuropsychological tests assessed global cognition and six cognitive domains, at baseline and 2, 4 and 6 years later. No associations were found between the Mediterranean or DASH dietary scores and overall cognition and cognitive decline over six years. But a higher intake of legumes and nuts was related to better overall performance in global cognition and to multiple cognitive domains, and to less decline in global cognition.

Higher habitual nuts consumption is associated with better cognitive function among Qatari adults. (Nafea et al, 2021).
This research looked at food frequency data from 1,000 Qatar-based adults (aged >20 years) and compared this with mean reaction time (MRT) – an indicator of cognitive function. Blood samples were also measured for magnesium, lipids and glucose. Eating nuts ≥4–6 times/week was linked with better cognitive function, compared with low consumption (≤1 time/month), especially in older adults (classed as those >50 years). The association between nuts consumption and MRT was not mediated by hypertension, diabetes or serum magnesium.

Associations between nut intake, cognitive function and non‐alcoholic fatty liver disease (NAFLD) in older adults in the United States: NHANES 2011-14. (Tan et al, 2021).
This study by Australian-based researchers found nut intake may increase cognitive performance in healthy older adults. It found cognitive scores were higher in people with a moderate intake of nuts, equivalent to 15-30g nuts daily, compared with those who didn’t eat nuts. The study involved 1,814 US-based adults aged 60 years or older, from the National Health and Nutrition Examination Surveys (NHANES) 2011-2012 and 2013-2014 cohorts. Eating more than 30g nuts/day did not lead to higher cognitive performance, compared to the moderate intake group. But higher nutrient intake and better diet quality were seen with higher nut intake.

Investigating walnut consumption and cognitive trajectories in a representative sample of older US adults. (Bishop et al, 2021).
Daily walnut consumption was linked with cognitive function at baseline in this observational study, involving 3,632 US-based adults aged 65 years and older. But walnut consumption was not associated with protection against age-related cognitive decline over time. It was, however, linked with a higher intake of nutrients identified to have neuroprotective benefits. This was a secondary analysis of the Health and Retirement Study and Health Care and Nutrition Study.

Nuts and older adults’ health: A narrative review. (Tan et al, 2021).
This review collated the findings from past studies which looked at the effects of nuts on age-related diseases. Specifically, the researchers considered the potential for nut consumption to effect telomere length, sarcopenia, and cognitive function – all major markers for age-related conditions. Based on data to date, they suggest that nut consumption, especially when part of a healthy diet or over a prolonged period, is linked with positive outcomes, such as longer telomere length, reduced risk of sarcopenia and better cognition. But further longer-term intervention studies are needed.

Effects of daily almond consumption for six months on cognitive measures in healthy middle-aged to older adults: A randomized control trial. (Mustra Rakic et al, 2021).
This randomised controlled trial looked at the impact of almonds on cognition in healthy, middle-aged/older adults (50–75 years). Subjects were assigned to either: 1.5 oz/d almond, 3 oz/d almond, or 3.5 oz/d snack (control group). Serum analyses for tocopherols, oxidative status and inflammation, and cognition were assessed at baseline, and 3 and 6 months later. At 6 months, alpha-tocopherol concentrations increased by 8% in the 3 oz almond group, but did not increase in the other groups. There was no change over time in cognitive function among the groups. But there was a significant improvement in some cognitive measures in the 3 oz/d almond group at 6 months. Note: 3 oz equates to around 85g.

Mediterranean diet, Alzheimer disease biomarkers and brain atrophy in old age. (Ballarini et al, 2021).
This study found that higher adherence to a Mediterranean diet may help prevent the build-up of amyloid protein and tau protein, which are linked with Alzheimer’s disease. It may also result in larger grey matter volume and better memory. The researchers say their findings corroborate the view of a Mediterranean diet as a protective factor against memory decline and mediotemporal atrophy. They propose that the risk of developing Alzheimer’s may be reduced by incorporating more elements of the Mediterranean diet into daily diets. The study involved 512 older adults (mean age: 69.5±5.9 years) – some at a higher risk of developing Alzheimer’s disease, while others were classed as ‘cognitively normal’. 

Consumption of dietary nuts in midlife and risk of cognitive impairment in late-life: the Singapore Chinese Health Study. (2020).
This prospective cohort study looked at data from 16,737 participants in the Singapore Chinese Health Study. Intake of nuts was assessed at 45–74 years old (mean age = 53.5 years), and cognitive function at 61–96 years old (mean age = 73.2 years). Cognitive impairment was found in 2,397 people. Compared with those who consumed <1 serving/month of nuts, participants who consumed ≥2 servings/week had a 21% lower risk of cognitive impairment. This was partly mediated by unsaturated fatty acid intake.

Dietary patterns and cognitive health in older adults: Findings from the Sydney Memory and Ageing Study. (2020).
This Australian study found healthy dietary patterns, including the Mediterranean and DASH diets, and greater consumption of nuts and legumes were linked with better cognition among older adults. The well-known population-based, cross-sectional Sydney Memory and Ageing Study involved 819 older Australians, aged 70–90 years.

A high polyphenol diet improves psychological wellbeing: The Polyphenol Intervention Trial. (2020).
This intervention study assessed the effect of a high polyphenol diet (HPD), compared to a low polyphenol diet, on aspects of psychological wellbeing. It involved 99 mildly-hypertensive participants, aged 40–65 years, and found people in the HPD group reported a decrease in depressive symptoms, and improvements in general mental health status and physical health. No differences in anxiety, stress, self-esteem or body image perception were observed. According to the researchers, the richest sources of polyphenols include nuts, seeds, fruits (eg. berries, grapes, apples and plums), vegetables (eg. cabbage, eggplant, onions, peppers), plant-derived beverages (including tea, coffee, red wine and fruit juices) and chocolate (particularly dark chocolate).

Plant-based diets for healthy ageing. (2020).
Kahleova H. et al. Modulating lifestyle risk factors and adopting healthful diets are powerful tools that may delay the aging process, decrease age-associated co-morbidities and mortality, and increase life expectancy – plant-based diets can slash the risk of developing metabolic syndrome and type 2 diabetes by about 50 percent, and may cut the risk of developing Alzheimer’s disease by more than 50 percent.

Legume and nut consumption in relation to depression, anxiety and psychological distress in Iranian adults. (2020).
Anjom-Shoae J. et al. The study was conducted with 3,172 adult participants aged 18-55 years. Researchers assessed the volunteers’ legume and nut consumption using a validated food frequency questionnaire. Consumption of legumes and nuts was associated with lower odds of anxiety in men. The researchers concluded that legume and nut consumption might be promising and, along with medications, could be used to prevent, control or delay psychological disorders.

Effect of a 12-Week Almond-Enriched Diet on Biomarkers of Cognitive Performance, Mood, and Cardiometabolic Health in Older Overweight Adults. (2020)
Coates A. et al
This study examined supplementing habitual diets with almonds or carbohydrate-rich snack foods (providing 15% energy) on biomarkers of cardiovascular and metabolic health, mood and cognitive performance. The inclusion of almonds in the diet improves aspects of cardiometabolic health without affecting cognitive performance or mood in overweight/obese adults.

Beneficial Effects of Walnuts on Cognition and Brain Health. (2020)
Chauhan. A. et al.
Researchers from the New York State Institute for Basic Research in Developmental Disabilities investigated in this field and suggested that a diet supplemented with walnuts (1-2 oz per day) may help reduce oxidative stress by decreasing the generation of free radicals and by boosting antioxidant defence. Also, evidence from animal and human studies suggests that dietary consumption of walnuts may help improve cognitive function (brain health) and may also reduce the risk of other diseases, such as cardiovascular disease, depression and type 2 diabetes, which are risk factors for the development of dementia.

Habitual Nut Exposure, Assessed by Dietary and Multiple Urinary Metabolomic Markers, and Cognitive Decline in Older Adults: The InCHIANTI Study. (2020).
This study showed that a high intake of nuts may help protect older adults from cognitive decline. A total of 119 participants aged 65 and over were selected from the InCHIANTI cohort. Participants were selected based on their nut intake: non-nut consumers and regular consumers (approx. 28g/week). Researchers found that nut consumption estimated either by dietary marker or urinary marker model was associated with lower cognitive decline.

Consumption of Nuts at Midlife and Healthy Aging in Women. (2020).
Results of this research showed a significant association between the consumption of nuts and healthy aging at midlife, and a greater likelihood of overall health and well-being at older ages. Walnuts appeared to have the strongest relation to healthy aging. The findings support the notion that long-term nut consumption merits as a strategy contributing to a healthier lifespan.

Habitual Nut Exposure, Assessed by Dietary and Multiple Urinary Metabolomic Markers, and Cognitive Decline in Older Adults: The InCHIANTI Study. (2020).
A high intake of nuts may protect older adults from cognitive decline.

Effect of a 2-year diet intervention with walnuts on cognitive decline. The Walnuts And Healthy Aging (WAHA) study: a randomized controlled trial. (2020).
Walnut supplementation for 2 y had no effect on cognition in healthy elders. However, brain fMRI and post hoc analyses by site suggest that walnuts might delay cognitive decline in subgroups at higher risk.

Promising results for walnuts in delaying cognitive decline – The Walnuts and Healthy Aging (WAHA) study: a randomized controlled trial
Although walnut supplementation had no effect on cognition in healthy aging adults, MRI results suggest that walnuts might delay cognitive decline in subgroups at higher risk. These encouraging but inconclusive results warrant further investigation, particularly targeting disadvantaged populations, in whom greatest benefit could be expected.

Almond, hazelnut and walnut, three nuts for neuroprotection in Alzheimer’s disease: A neuropharmacological review of their bioactive constituents. (2018).
There is evidence that almond, hazelnut and walnut have bioactive properties that influence mechanisms that may be involved in the development of Alzheimer’s disease, although clinical trials in humans that directly test the relationship between these nut types and Alzheimer’s disease are lacking.

Maternal nut intake in pregnancy and child neuropsychological development up to 8 years old: a population-based cohort study in Spain. (2019).
In the first of its kind, a study led by the Barcelona Institute for Global Health found children, whose mothers ate more nuts during the first trimester of pregnancy, achieved the best results in tests measuring cognitive function, attention capacity and working memory.

A Prospective Association of Nut Consumption with Cognitive Function in Chinese Adults aged 55+ China Health and Nutrition Survey. (2019).
Eating more than 10g of nuts a day may improve thinking, reasoning and memory, and keep age-related mental disorders at bay. The study by researchers from the University of South Australia was conducted on over 4,000 Chinese adults aged over 55 years.

Lower Depression Scores among Walnut Consumers in NHANES. (2019).
New study in US population finds nut consumers, and particularly walnut consumers have significantly lower prevalence and frequency of depressive symptoms compared to non-nut consumers.

Nut consumption for vascular health and cognitive function. (2014).
Nut consumption reduces blood pressure and improves glucoregulation, endothelial vasodilator function and inflammation, whilst a limited number of studies suggest that nut consumption may also improve cognitive performance. Further clinical trials are warranted to explore relationships between nut consumption, endothelial function and cognitive function.

Nut consumption and age-related disease. (2016).
Nuts show promise as useful adjuvants to prevent, delay or ameliorate a number of chronic conditions in older people. Their association with decreased mortality suggests a potential in reducing disease burden, including cardiovascular disease, cancer, and cognitive impairments.

The Mediterranean diet impact on prevention and treatment of cognitive decline. (2017)
A healthy Mediterranean diet (MeDi), rich in fruit, vegetables, whole grains, nuts, olive oil, and fish may be neuroprotective. Greater adherence to the MeDi is associated with slower rate of cognitive decline and lower risk of cognitive impairment and dementia, but findings are conflicting, mainly due to significant heterogeneity between studies in terms of populations studied and methods used to assess diet and cognition.

Role of walnuts in maintaining brain health with age. (2014).
English walnuts (Juglans regia L.) are rich in numerous phytochemicals, including high amounts of polyunsaturated fatty acids, and offer potential benefits to brain health. Polyphenolic compounds found in walnuts not only reduce the oxidant and inflammatory load on brain cells but also improve interneuronal signalling, increase neurogenesis, and enhance sequestration of insoluble toxic protein aggregates.

Cognition: the new frontier for nuts and berries. (2014).
Regular nut consumption, berry consumption, or both could possibly be used as an adjunctive therapeutic strategy in the treatment and prevention of several neurodegenerative diseases and age-related brain dysfunction. A number of animal and a growing number of human studies show that moderate-duration dietary supplementation with nuts, berry fruit, or both is capable of altering cognitive performance in humans, perhaps forestalling or reversing the effects of neurodegeneration in ageing.

Dietary patterns: a new therapeutic approach for depression. (2018).
Most studies showed an inverse association between healthy dietary patterns, rich in fruits, vegetables, lean meats, nuts and whole grains, and with low intake of processed and sugary foods, and depression and depressive symptoms throughout an array of age groups, although some authors reported statistical significance only in women.

Food patterns and the prevention of depression. (2016).
According to large and well-conducted observational studies, food patterns potentially associated with reduced risk of depression are those emphasising seafood, vegetables, fruits and nuts.


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