Daily consumption of unsalted, skin-roasted peanuts beneficially affects regional brain insulin responsiveness in older adults: results of a longer-term randomized controlled trial

Brain insulin responsiveness is implicated in age-related metabolic and cognitive conditions. We previously reported that daily consumption of unsalted, skin-roasted peanuts improved memory in older adults. Here, we investigated whether changes in brain insulin responsiveness may contribute to these effects. In a randomized, single-blind, controlled crossover study, 31 older adults (67 ± 4 years) consumed either 60 g day-1 of unsalted, skin-roasted peanuts or followed a no-peanut control period for 16 weeks, separated by an 8-week washout. Brain insulin responsiveness was assessed as changes in cerebral blood flow (CBF) following intranasal insulin administration using arterial spin labeling magnetic resonance imaging (ASL-MRI). Intrahepatic lipid (IHL) content was quantified using abdominal MRI. Fasting blood samples were evaluated for markers of glucose homeostasis, lipid metabolism, and low-grade systemic inflammation. Whole-brain analysis identified one region in the right hemisphere showing reduced CBF responses to intranasal insulin after peanut intake compared with the control (mean difference: -5.4 ± 5.4 mL per 100 g tissue per min; cluster size = 552 mm3, P = 0.044). Harvard-Oxford atlas localization yielded the highest average probabilities for the lingual gyrus (20%), hippocampus (14%), parahippocampal gyrus (11%), thalamus (2%), and posterior cingulate gyrus (1%). Intrahepatic lipid content and circulating markers of glucose homeostasis, lipid metabolism, and low-grade systemic inflammation remained unchanged. These findings suggest that 16 weeks of unsalted, skin-roasted peanut consumption had a potentially beneficial effect on regional brain insulin responsiveness in memory-related brain regions in older adults. This response may contribute to the previously observed cognitive benefits of peanut intake in this population. Clinical Trial Registry: This trial was registered at clinicaltrial.gov as NCT05724654.