Do Hazelnuts Sharpen Memory? A Trial Measured with Brain MRI

The effect of diet on brain health is one of the most discussed and least well-evidenced areas in nutrition. On nuts, however, there are measurable data, obtained through brain imaging.

How the trial was designed

In a randomised controlled crossover trial published in Clinical Nutrition, 28 healthy participants with a mean age of 65 took part. Their average body mass index was 27.9.

For 16 weeks participants consumed **60 grams of mixed nuts daily** (walnuts, pistachios, cashews and hazelnuts). During the control period they ate no nuts. An eight-week washout separated the two phases.

The measurement method matters here: cerebral blood flow was quantified using **arterial spin labelling magnetic resonance imaging**. Cognitive performance was assessed with the Cambridge Neuropsychological Test Automated Battery.

In other words, the study did not rely on "how do you feel" but on instrument-based data.

The results

Compared with the control period, the nut period produced **higher regional cerebral blood flow in the right frontal and parietal lobes** (treatment effect: 5.0 ± 6.5 mL/100 g/min; p < 0.001). A similar increase was seen in the left frontal lobe.

Verbal memory improved.

An important detail: **body weight remained stable throughout the study.** Adding 60 grams of nuts a day did not cause weight gain.

Why does cerebral blood flow matter?

The brain makes up about 2% of body weight but consumes a far greater share of energy, delivered through continuous blood flow.

Vascular function weakens with age and cerebral blood flow declines. That decline is one of the factors associated with cognitive deterioration.

The study also assessed endothelial function, arterial stiffness and the retinal microvasculature, all different markers of vascular health.

The bigger picture: a review of 43,793 people

In a systematic review published in Advances in Nutrition, four databases were searched and **22 studies** meeting the criteria were selected from 2,374 articles. Together they covered **43,793 participants**.

Outcomes examined included immediate and delayed memory, attention, processing speed, executive function, visual-spatial ability and risk of mild cognitive impairment.

The review's general conclusion is that nut consumption may be associated with cognitive performance, while noting methodological differences between studies.

Observational data from Italy

A cross-sectional analysis of 883 people aged 50 and over was drawn from the MEAL study in southern Italy.

Nut consumption was measured with a 110-item questionnaire covering almonds, walnuts, hazelnuts, peanuts and chestnuts separately. Cognitive function was assessed with a validated mental status questionnaire.

Comparing high and low nut consumers, higher consumption was associated with better cognitive status.

One caveat: this is a **cross-sectional study**, so it does not establish cause and effect. People who eat nuts may simply lead healthier lives overall.

Possible mechanisms

Preclinical work suggests compounds in nuts may reduce oxidative stress, counteract beta-amyloid buildup and support endothelial function.

The vitamin E content of hazelnuts stands out here: about 15 mg per 100 g. Vitamin E is a fat-soluble antioxidant and brain tissue is rich in fat.

Monounsaturated fatty acids may also act indirectly through vascular function.

These remain proposed mechanisms rather than chains proven in humans.

Not overstating it

A cross-sectional sub-analysis of the five-year PREDIMED trial contains an interesting finding: of all the foods considered, only olive oil, coffee, wine and **walnuts**, not total nuts, were related to better cognitive function.

That suggests different nuts may have different effects and that no single food should be overstated.

The MRI trial above also involved only 28 people and was funded by the International Nut and Dried Fruit Council. That does not invalidate the result, but it is worth keeping in mind.

Practical takeaway

A handful of nuts a day is below the amounts used in these trials but a reasonable starting point.

Brain health does not depend on a single food. Sleep, physical activity, blood pressure control and social interaction matter at least as much as diet.

If you are concerned about cognitive decline, discuss it with your doctor; this article is for information only.

Sources

Nijssen K.M.R. et al., "Longer-term mixed nut consumption improves brain vascular function and memory: A randomized, controlled crossover trial in older adults", Clinical Nutrition, 2023.

Cardoso B.R. et al., "Nut Consumption for Cognitive Performance: A Systematic Review", Advances in Nutrition, 2021.

Cross-sectional analysis from the MEAL study, nut consumption and cognitive status, Nutrients, 2025.

"Impact of Nut Consumption on Cognition across the Lifespan", review including the PREDIMED sub-analysis.