TL;DR
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A randomized crossover trial in 31 older adults found that 16 weeks of eating 60 grams of unsalted, skin-roasted peanuts daily was associated with a lower blood-flow response to intranasal insulin in a cluster of right-brain regions, including the hippocampus. The scan measured blood-flow changes as an indirect indicator of brain insulin responsiveness; the result does not show that peanuts prevent cognitive decline or improve memory.
A 16-week randomized crossover trial found that older adults who ate 60 grams of unsalted, skin-roasted peanuts daily had a different blood-flow response to intranasal insulin in several right-brain regions, including the hippocampus, than during a no-peanut period. The finding offers a possible clue about how diet relates to brain insulin responsiveness, but the study was small and used an indirect measure; it does not establish that peanuts improve memory or protect against dementia.
The study, published in Food & Function, enrolled 36 participants, of whom 31 completed both phases: 15 women and 16 men, with a mean age of 67. Each participant followed a 16-week peanut diet and a 16-week control period without peanuts or other nuts, with an eight-week washout between them. The order of the periods was randomized.
At the end of each period, researchers used arterial spin labeling MRI to measure cerebral blood flow before and after intranasal insulin. The change in blood flow served as an indirect measure of regional brain insulin responsiveness, not a direct reading of neuronal insulin signaling. After the peanut period, a cluster primarily involving the right lingual gyrus, hippocampus and parahippocampal gyrus showed a significantly lower blood-flow response to insulin than after the control period.
Participants generally tolerated the intervention and compliance was reported as excellent. One participant withdrew because of gastrointestinal discomfort after eating peanuts. The report states that there were no study-related serious adverse events; one serious event during the control period was unrelated. Body measurements remained stable, while total energy intake rose during the peanut phase and participants’ diets shifted toward more unsaturated fat and fiber and less carbohydrate, saturated fat and cholesterol.
What the Brain Scan Can Show
The results add a measured brain response to research on how food may relate to cognitive and metabolic processes in older adults. The hippocampus and nearby regions are involved in memory, and brain insulin signaling has been studied in connection with age-related cognitive changes. A change in the MRI response may help researchers frame questions about diet and brain function, but it is not itself evidence of better cognition.
The distinction matters for readers: the trial measured blood-flow changes after insulin, not memory improvement, dementia risk or a clinical outcome. The finding also does not show that a daily peanut serving has the same effect for everyone or that it should replace established medical care. It is a result from a small, selected group, and its practical meaning needs further testing.
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How the Trial Was Designed
The research followed earlier studies suggesting that skin-roasted peanuts may affect brain vascular function and memory in older adults. This trial asked whether changes in brain insulin responsiveness might be related to those previously reported effects. It was a randomized, single-blind, controlled crossover study: participants served as their own comparison by completing both the peanut and no-peanut periods.
Participants were aged 60 to 75 and had a body mass index between 20 and 35. The eligibility criteria excluded people with peanut allergies and certain major health conditions or medications that could affect outcomes. They consumed prepackaged portions during the intervention and were asked to avoid peanuts, other nuts and some nutritionally similar seeds during the control period. Consequently, the findings apply most directly to this specific group and study routine, not automatically to all older adults or to other forms and amounts of peanuts.
“The insulin-induced changes in cerebral blood flow served as an indirect measure of regional brain insulin responsiveness.”
— The study authors, as described in the News-Medical report
What the Result Cannot Establish
The supplied report does not provide the size of the blood-flow difference, the full statistical results or evidence that the change translated into a difference in participants’ memory or daily functioning. It also does not establish whether the observed response is beneficial, how long it lasts after people stop eating peanuts, or whether it appears in other brain regions or populations.
Because the intervention changed overall energy intake and several nutrients, it remains uncertain whether the result was specifically related to peanuts, to their nutrient profile, or to the broader dietary shift. With 31 trial completers and a selected sample, larger studies would be needed to test how reliable and broadly applicable the finding is.
Further Trials Must Test Relevance
The study report does not specify a follow-up trial or a date for additional results. The next research step would be to replicate the brain-response finding in a larger and more diverse group, report the magnitude and precision of the effect, and examine whether it tracks with measurable cognitive outcomes over time. Researchers would also need to separate the effects of peanuts from those of changes in overall calories and other nutrients before drawing conclusions about diet recommendations.
Key Questions
How many peanuts did participants eat each day?
During the intervention, participants ate 60 grams of unsalted, skin-roasted peanuts daily for 16 weeks.
Did the study show that peanuts improve memory?
No. This trial measured brain blood-flow responses after intranasal insulin. It did not establish that the participants’ memory improved during the intervention.
What does a lower blood-flow response mean?
The researchers treated changes in cerebral blood flow as an indirect indicator of regional brain insulin responsiveness. The report does not establish whether the lower response is clinically beneficial or harmful.
Can the findings be applied to everyone?
Not on this evidence alone. The trial had 31 completers aged 60 to 75 who met specific eligibility criteria, so additional research is needed to determine whether the result applies to other groups.
Source: news-medical.net
