A new study in Clinical Nutrition provides evidence that the regular consumption of unsalted, skin-roasted peanuts may enhance brain vascular function and memory in older adults. The research indicates that eating a moderate daily amount of peanuts improves blood flow to specific regions of the brain and aids in the retention of verbal information.
As individuals age, the vascular system in the brain often undergoes changes that can reduce the efficiency of blood flow. This reduction in cerebral blood flow is a known physiological marker associated with cognitive decline and neurodegenerative conditions such as dementia.
Because the delivery of oxygen and nutrients is vital for maintaining neuronal health, researchers have focused on identifying modifiable lifestyle factors that can support vascular function. Diet is considered a significant factor in this regard.
While peanuts are botanically classified as legumes rather than tree nuts, they share a comparable nutritional profile. They are dense in protein, unsaturated fatty acids, and fiber. The researchers, led by Peter J. Joris and Lucia Kerkhof, initiated this study to investigate whether peanuts specifically could offer neuroprotective benefits similar to those observed with tree nuts.
A primary motivation for the trial was the high content of L-arginine found in peanuts. L-arginine is an amino acid that serves as a precursor for the synthesis of nitric oxide, a molecule essential for relaxing blood vessels and regulating blood flow.
Additionally, the study focused on skin-roasted peanuts because the peanut skin is rich in bioactive compounds, including polyphenols like resveratrol, which have antioxidant properties that may further support vascular health.
“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,” said Joris, an associate professor at the Institute of Nutrition and Translational Research in Metabolism (NUTRIM) at Maastricht University.
“As researchers studying nutrition and brain health, we are very interested in how the food we consume can support healthy aging. Peanuts are widely consumed, affordable, and nutrient-dense, yet relatively little was known about their specific effects on the brain.”
“Earlier work from our group showed that mixed nuts can improve memory and blood flow in the brain in older adults. Adequate blood flow in the brain is important for the delivery of oxygen and nutrients to the brain cells. Without enough oxygen and nutrients, the highly metabolically active brain cannot function properly, and key functions like memory can be affected.”
“In this study, we sought to determine whether peanuts, which are botanically classified as legumes rather than nuts, also exert beneficial effects on brain health,” Joris explained.
To test the effects of peanut consumption, the investigators designed a randomized, single-blind, controlled crossover trial. This study design allowed each participant to serve as their own control, reducing variability caused by individual differences.
The research team recruited 31 healthy older adults ranging in age from 60 to 75 years. The participants included both men and women with body mass indexes between 20 and 35 kg/m ². Individuals were excluded if they had a history of cardiovascular disease, diabetes, peanut allergies, or if they were current smokers.
The study consisted of two 16-week periods separated by an eight-week washout phase. During the intervention period, participants consumed 60 grams of unsalted, skin-roasted peanuts daily. This portion size is approximately equivalent to two servings or two handfuls.
The peanuts were of the runner variety and were eaten with the skins intact. Participants were instructed to incorporate the peanuts into their regular diet but were not permitted to heat or crush them, as this might alter their nutritional properties. During the control period, participants refrained from eating peanuts and avoided other nut-based products to ensure a clear comparison.
The primary measure for the study was cerebral blood flow, assessed using a non-invasive imaging technique called pseudo-continuous arterial spin labeling magnetic resonance imaging. This advanced method allows researchers to quantify the amount of blood reaching brain tissue without the use of radiation or contrast dyes.
Secondary outcomes included cognitive performance, which was evaluated using the Cambridge Neuropsychological Test Automated Battery, a series of computerized tests designed to measure memory, psychomotor speed, and executive function. The researchers also monitored blood pressure and gathered data on dietary intake through food frequency questionnaires.
The imaging results revealed a statistically significant improvement in brain vascular responsiveness following the peanut intervention. Global cerebral blood flow increased by 3.6 percent compared to the control period.
When the analysis focused specifically on gray matter, which contains the cell bodies of the brain’s neurons, the increase in blood flow was 4.5 percent. The researchers observed regional improvements as well. Blood flow increased by 6.6 percent in the frontal lobes and 4.9 percent in the temporal lobes. These areas of the brain are intimately involved in processing memories, language, and executive control.
“We were intrigued to see improvements not only in specific brain regions, but also at the whole-brain level,” Joris told PsyPost. “That indicates a more widespread effect on brain vascular function than what we observed in earlier studies.”
In parallel with the physiological changes, the researchers identified improvements in cognitive function. Participants demonstrated a 5.8 percent increase in verbal memory performance. This was measured by a delayed recall task where participants were asked to identify words they had seen on a list twenty minutes earlier. Those who had consumed the peanuts were able to correctly recognize more words than they did during the control period.
“Our results suggest that eating unsalted, skin-roasted peanuts every day can support brain health as we age,” Joris said. “After 16 weeks, participants showed better brain blood flow and improved memory.”
While memory improved, the study did not find significant changes in executive function or psychomotor speed. There was a slight increase in reaction latency during one of the multitasking tests, which the authors suggest might reflect a trade-off where participants prioritized accuracy over speed, although this particular finding requires further verification.
Beyond brain health, the intervention appeared to benefit cardiovascular metrics. Systolic blood pressure, the top number in a blood pressure reading, decreased by an average of 5 mmHg during the peanut consumption phase. Pulse pressure, which represents the difference between systolic and diastolic blood pressure, decreased by 4 mmHg. These reductions are relevant for older adults, as elevated blood pressure is a risk factor for both cardiovascular disease and cognitive impairment.
Dietary analysis confirmed that during the peanut intervention, participants had higher intakes of total fat, monounsaturated fatty acids, and fiber, while their carbohydrate intake was lower.
Despite the addition of approximately 340 calories per day from the peanuts, body weight remained generally stable across the study population, though there was a minor interaction effect depending on the order in which the participants completed the intervention and control phases. This suggests that participants may have naturally adjusted their intake of other foods to compensate for the added peanuts.
The study has several limitations that provide context for the findings. Due to the nature of the dietary intervention, it was not possible to blind the participants to the fact that they were eating peanuts. This awareness could potentially influence their behavior or self-reported data, although the researchers analyzing the MRI and cognitive data remained blinded to the treatment conditions.
Additionally, while the results show a clear association between peanut consumption and improved vascular function, the specific biological mechanism remains to be fully elucidated. It is not yet known if the effects are driven primarily by L-arginine, the phenolic compounds in the skins, the fatty acid profile, or a synergistic combination of these nutrients.
The research was funded by The Peanut Institute Foundation. The authors state that the funding body had no role in the design of the study, the collection and analysis of data, or the decision to publish the results. The authors declared no conflicts of interest.
Future research directions include investigating whether different forms of peanut products offer similar benefits. The investigators also aim to explore the dose-response relationship to determine if smaller amounts of peanuts could yield comparable results.
“We would like to examine whether different peanut preparations, such as peanut butter, produce similar effects,” Joris said. “In addition, we seek to clarify which peanut components may underlie the observed benefits. To this end, we are now conducting a study assessing the effects of protein on the same outcomes, given that peanuts are rich in protein.”
“One important point is that the peanuts were unsalted and skin-roasted,” the researcher added. “The skin contains many antioxidants and fibre that may contribute to the beneficial effects.”
The study, “Longer-term skin-roasted peanut consumption improves brain vascular function and memory: A randomized, single-blind, controlled crossover trial in healthy older adults,” was authored by Lucia Kerkhof, Ronald P. Mensink, Jogchum Plat, Kevin M. R. Nijssen, and Peter J. Joris.
