A recent study published in Clinical Nutrition evaluated the long-term effects of the consumption of various nuts on brain vascular function and cognitive performance.

Study: Longer-term mixed nut consumption improves brain vascular function and memory: a randomized, controlled crossover trial in older adults. Image Credit: umaruchan4678 / Shutterstock.com

The health advantages of nuts

Dietary interventions are effective approaches to cut back the burden of or prevent age-related conditions, including cognitive decline and heart problems. To this end, previous studies suggest that nut consumption is protective against cognitive impairment.
Studies that include nuts within the Mediterranean food plan have also reported cognitive advantages in older adults. Likewise, randomized controlled trials (RCTs) have demonstrated the advantages of nuts on impaired vascular function; nevertheless, there is restricted evidence for the consequences of nut consumption on central arteries near the brain.

Concerning the study

In the current study, researchers evaluate the consequences of long-term consumption of mixed nuts on brain vascular function in older individuals. Eligible participants were healthy males and post-menopausal females between 60 and 70 years of age, with stable body weight and body mass index (BMI) between 25 kg/m² to 35 kg/m². Subjects were excluded in the event that they had nut intolerance or allergy, conditions interfering with study outcomes, or contraindications for magnetic resonance imaging (MRI).

The present study was a single-blinded RCT with a cross-over design, including 16-week intervention and control periods and an eight-week washout period in between. In the course of the intervention period, participants consumed 60 grams of mixed nuts, including cashews, walnuts, hazelnuts, and pistachios, day by day.

Participants were instructed to stick to Dutch food-based dietary guidelines and never eat products wealthy in n3-poly-unsaturated fatty acids (PUFAs). Peripheral and brain vascular function and cognitive performance were assessed at the top of every period. Cerebral blood flow (CBF) was quantified using pseudo-continuous arterial spin labeling MRI.

Cognitive performance was examined using the Cambridge neuropsychological test automated battery. Moreover, effects on retinal microvasculature, arterial stiffness, and endothelial function were investigated. Differences between intervention and control periods were assessed using linear mixed models.

Study findings

Twenty-eight individuals were included in the present study, with each sexes represented equally. The common age of the participants was 64.6, with a median BMI of 27.9 kg/m².

The mixed-nut intervention was well-tolerated, and no protocol deviations or serious opposed events were reported. The intervention resulted in a decrease in cholesterol and carbohydrate intake and a rise in fiber intake as compared to regulate.

Total fat intake was higher after mixed nut intervention, with a lower intake of saturated fatty acids (SFAs) and the next intake of cis-monounsaturated fatty acids (cis-MUFAs), alpha-linolenic acid, linolenic acid, and cis-PUFA. SFAs were 0.9 percentage points lower after the intervention, primarily as a consequence of decreased palmitic acid.

Total PUFAs were 1.3 percentage points higher, whereas total MUFAs remained unchanged with the intervention. There have been no significant differences between intervention and control periods when it comes to whole-brain, cortical, sub-cortical, or grey matter CBF. Nevertheless, the cluster-wise evaluation indicated a significantly higher regional CBF across three clusters.

CBF increased in cluster one by 5 ml/100 g/min. The mean probability of its location was in the best superior parietal lobe, lateral occipital cortex, and superior frontal, precentral, postcentral, and middle frontal gyri. CBF increased in clusters two and three by 5.4 ml/100 g/min and 5.6 ml/100 g/min, respectively.

The mean probability of the placement of cluster two was the left precentral, middle frontal, superior frontal, and postcentral gyri. The common probability of the placement of cluster three was bilateral within the frontal medial cortex, frontal pole, and cingulate and paracingulate gyri. Carotid artery reactivity was 0.7 percentage points higher after intervention than control.

The intervention significantly reduced carotid-to-femoral pulse wave velocity. After the intervention, brachial artery flow-mediated vasodilation, central retinal arteriolar equivalent, and arteriolar to venular ratio were higher. The central retinal venular equivalent was not different after the intervention.

Performance in a visuospatial memory task improved after the intervention, with the variety of correct words in a verbal memory task increasing by 16% after the intervention. There have been no differences between intervention and control periods in word recognition, psychomotor speed, executive function, stress, quality of life, sleep quality, and mood.

Conclusions

A rise in regional CBF was observed inside three clusters within the left frontal lobe, bilateral prefrontal cortex, and right parietal and frontal lobe following the mixed nut intervention.

Improvements in cognitive performance inside the memory domain were also observed without changes in psychomotor speed and executive function. Likewise, improvements in numerous characteristics of the peripheral vascular tree were evident after the mixed nut intervention.