Daily handful of peanuts improved brain blood flow and memory in older adults, two studies find

Two handfuls of peanuts a day — about 60 grams — improved blood flow to the brain, boosted verbal memory, and made key memory-related brain regions more responsive to insulin in healthy adults aged 60 to 75, according to a pair of linked studies out of Maastricht University Medical Center in the Netherlands.

The newer findings, published in the peer-reviewed journal Food & Function, focus on how the brain handles insulin — a hormone whose role extends well beyond blood sugar. In the brain, insulin helps nerve cells grow, survive, and communicate, and weakening insulin signaling has been linked to age-related cognitive decline and processes associated with Alzheimer's disease. After 16 weeks of daily peanut consumption, participants showed improved insulin responsiveness in a cluster of brain regions in the right hemisphere, including portions of the hippocampus, lingual gyrus, parahippocampal gyrus, and posterior cingulate gyrus — all involved in memory.

Our study found that daily peanut consumption beneficially affected insulin responsiveness in memory-related brain regions in older adults. These findings suggest that enhanced regional brain insulin responsiveness may contribute to the cognitive benefits of unsalted, skin-roasted peanut intake.— Dr. Peter Joris, Associate Professor, Department of Nutrition and Movement Sciences, NUTRIM, Maastricht University Medical Center

That study builds directly on earlier Maastricht research published in Clinical Nutrition, which measured what the same daily peanut regimen did to blood flow and memory. That trial found global cerebral blood flow rose by 3.6 percent compared to the control period. When researchers looked only at gray matter — the tissue containing the brain's neuron cell bodies — the increase was 4.5 percent. Blood flow to the frontal lobes climbed 6.6 percent and to the temporal lobes 4.9 percent, regions central to memory, language, and executive control. Verbal memory performance improved by 5.8 percent, according to psypost.org.

We were intrigued to see improvements not only in specific brain regions, but also at the whole-brain level. That indicates a more widespread effect on brain vascular function than what we observed in earlier studies.— Dr. Peter Joris, Associate Professor, Maastricht University

Both trials used the same rigorous design: a randomized, controlled crossover trial with 31 healthy older adults. Each participant went through two 16-week phases — one eating peanuts daily, one avoiding them entirely — separated by an eight-week washout period, so each person served as their own control. During the peanut phase, participants received premeasured packets of unsalted, skin-roasted runner-variety peanuts with the skins intact, and were free to eat them in the morning, afternoon, all at once, or spread through the day. They were not permitted to heat or crush the peanuts, as that could alter their nutritional properties. During the control phase, participants also avoided other nut-based products.

To measure brain blood flow, researchers used arterial spin labeling MRI, a non-invasive technique that quantifies blood reaching brain tissue without radiation or contrast dyes. Insulin responsiveness was assessed by tracking changes in regional cerebral blood flow after insulin was delivered through the nose. Cognitive performance was evaluated using the Cambridge Neuropsychological Test Automated Battery, a standardized set of computerized tests covering memory, psychomotor speed, and executive function.

Why peanuts specifically? The researchers point to several overlapping mechanisms rather than a single nutrient. Peanuts are dense in unsaturated fatty acids, dietary fiber, plant-based protein, vitamins, minerals, and bioactive compounds. The skin of the peanut is particularly rich in polyphenols including resveratrol, which has antioxidant properties that may support vascular health. The researchers also highlight L-arginine, an amino acid found in high concentrations in peanuts.

Multiple nutrients present in peanuts, including unsaturated fats, dietary fiber, vitamins and minerals and bioactive phytochemicals, could potentially contribute to the observed brain benefits. Peanuts are also a good source of plant-based protein and are especially rich in L-arginine. L-arginine is a key precursor of nitric oxide (NO), which has been reported to facilitate learning and memory performance.— Dr. Peter Joris, Associate Professor, Maastricht University Medical Center

The research was led by principal investigator Dr. Peter J. Joris and conducted by Ph.D. candidate Lucia Kerkhof of the Department of Nutrition and Movement Sciences at Maastricht University Medical Center. Funding came from The Peanut Institute Foundation; the researchers state the foundation had no involvement in designing or conducting the study, analyzing results, or preparing the manuscript.

The studies are small — 31 participants each — and the researchers themselves note that larger trials are needed before conclusions can be drawn about long-term effects on cognitive decline or dementia risk. The work was motivated in part by earlier Maastricht findings that mixed nuts improved memory and brain blood flow in older adults; this research asked whether peanuts, botanically a legume rather than a tree nut, could produce similar effects on their own.

The number of people who suffer from age-related cognitive decline or are diagnosed with dementia is increasing rapidly. Currently, dementia is ranked as the 7th leading cause of death worldwide according to the World Health Organization. Peanuts are widely consumed, affordable, and nutrient-dense, yet relatively little was known about their specific effects on the brain.— Dr. Peter Joris, Associate Professor, Maastricht University

Why it matters — With dementia ranked the seventh leading cause of death worldwide, these findings point to a cheap, widely available food that may support brain vascular health and memory in older adults — though the small sample sizes mean larger trials are needed before firm recommendations can be made.

Reported by sciencedaily.com, psypost.org