Walnuts, thinking skills and risk factors for decline
What it found
In people, walnut intake was linked to better thinking scores in studies that observe habits, but short trials found no clear effect on overall thinking or mood.
Trials also found no clear effect on blood sugar control or inflammation markers.
What they found
Studies in people
Thinking in trials
None of the 5 trials found a clear effect of walnuts on overall thinking scores. Three trials did find improvements in some specific thinking areas or in some groups of people.
Thinking in habit studies
All 7 studies that tracked people's usual eating habits found links between eating more walnuts and better thinking-related scores, with signs that more walnuts went with better scores.
Blood sugar control
Across 27 trials, walnuts did not clearly change HbA1c or insulin resistance compared with control. The authors rated their confidence in this as moderate.
Inflammation markers
Across the trials, walnuts did not clearly change hsCRP, IL-6, TNF-alpha, E-selectin, sICAM-1 or sVCAM-1 compared with control. The authors rated their confidence in this as moderate.
Mood
Three short trials in healthy young adults found no clear difference in mood between walnuts and control. One of these found better total mood scores in men only.
Stroke
Two analyses of large groups of health professionals found that people who ate more walnuts had a lower risk of stroke. These were studies of habits, not trials.
What the authors conclude
“In conclusion, the existing evidence, although with low level of confidence, suggests that walnut intake may have a beneficial effect on cognition-related outcomes, including cognitive function, mood, and stroke.”
Also in their conclusions
- They say the evidence is not enough to draw a firm conclusion about whether walnuts affect thinking or the risk factors for decline in adults.
- They call for high-quality studies with standard tests and doses to clarify the role of walnuts in cognitive health.
- They suggest future trials should focus on people at higher risk, such as those with high blood fats, and use markers of walnut intake instead of relying on people's memory of what they ate.
How it was done
Age-related cognitive decline is expected to grow as people live longer, and the authors wanted to see whether a cheap, easy food like walnuts could help protect thinking skills.
They pooled 32 randomised trials and 7 observational studies in adults, looking at walnut intake and thinking, mood, stroke, blood sugar control and inflammation. Trial doses ranged from about 15 to 99 grams of walnuts a day, and study lengths ranged from a few days to 14 months.
What it can’t tell you
- The studies that followed people over time can show a link between walnut habits and thinking, but they cannot prove that walnuts caused the difference.
- The trials were short and used many different thinking tests, so they cannot show whether walnuts affect long-term cognitive decline.
- The trials did not test whether walnuts prevent dementia or Alzheimer's disease.
Who paid
- Conflicts
- No potential conflict of interest was reported by the author(s).
- Authors work at
- Tufts University, USA; Tufts University School of Medicine, USA; Institute for Clinical Research and Health Policy Studies, USA
The paper
- Title
- Walnut intake, cognitive outcomes and risk factors: a systematic review and meta-analysis
- Type
- Systematic review and meta-analysisThe authors follow a set, published method to find every relevant study, then combine the numbers from them into one result.
- Evidence
- Studies in people
- Summarised from
- Full text
- Cite
- Cahoon D, Shertukde SP, Avendano EE, et al (2021). Walnut intake, cognitive outcomes and risk factors: a systematic review and meta-analysis. Annals of medicine. doi:10.1080/07853890.2021.1925955Free full textPubMed 34132152DOI
Summary written 26 Sep 2026. Check it against the paper before it changes what you eat. How we summarise papers · Report an error