Daily consumption of unsalted, skin-roasted peanuts for 16 weeks may beneficially affect regional brain insulin responsiveness in older adults, according to a study published in Food & Function. Researchers identified changes in insulin-induced cerebral blood flow in brain regions involved in memory processing, although these changes were not significantly associated with previously reported improvements in verbal recognition memory.
The randomized, single-blind, controlled crossover trial included 31 adults aged 60 to 75 years who completed the study. Participants had a mean age of 67 years, and 15 were women. Each participant consumed 60 g of unsalted, skin-roasted peanuts daily for 16 weeks and completed a 16-week control period without nuts, with an 8-week washout between interventions. The researchers randomly assigned participants to the intervention sequence.
Researchers assessed brain insulin responsiveness by measuring cerebral blood flow before and 30 minutes following intranasal administration of 160 IU of insulin using arterial spin labeling magnetic resonance imaging. Additional assessments included intrahepatic lipid content, glucose homeostasis, lipid metabolism, and markers of low-grade systemic inflammation. The researchers also examined associations between changes in brain insulin responsiveness and verbal recognition memory, which had improved following peanut consumption in a previously published analysis of the same trial.
Whole-brain analysis identified 1 cluster in the right hemisphere with a statistically significant reduction in insulin-induced cerebral blood flow responses following peanut consumption compared with the control period. The mean difference was −5.4 mL per 100 g of brain tissue per minute, and the affected cluster measured 552 mm³.
Anatomical mapping indicated that the cluster encompassed portions of the lingual gyrus, hippocampus, parahippocampal gyrus, thalamus, and posterior cingulate gyrus. The highest average localization probabilities were in the lingual gyrus (20%), hippocampus (14%), and parahippocampal gyrus (11%). These regions are involved in memory-related processes, and researchers suggested the reduced cerebral blood flow response to intranasal insulin may reflect more efficient or better-regulated neuronal activity.
However, the changes were region-specific. Researchers found no statistically significant differences in insulin-induced cerebral blood flow responses at the global, gray matter, cortical, or subcortical levels. Furthermore, changes in regional brain insulin responsiveness were not significantly associated with improvements in verbal recognition memory previously observed in the same study population.
Peanut consumption also had no statistically significant effect on intrahepatic lipid content. Mean liver fat content was 5.3% following the peanut intervention compared with 5.0% during the control period. Fasting glucose, insulin concentrations, and insulin resistance, assessed using the homeostasis model assessment of insulin resistance, remained unchanged.
Similarly, researchers found no statistically significant differences in total cholesterol, low-density lipoprotein cholesterol, or high-density lipoprotein cholesterol concentrations. Triglyceride concentrations were lower following 8 weeks of peanut consumption, with a mean difference of −0.20 mmol/L compared with the control period, but this difference was no longer evident at week 16. High-sensitivity C-reactive protein concentrations also remained unchanged.
Adherence to the intervention was high, with a median adherence rate of 100%. One participant withdrew because of gastrointestinal discomfort following peanut consumption. No study-related serious adverse events were reported by participants. Although peanut consumption increased total energy intake, waist circumference and body fat percentage remained unchanged.
Researchers acknowledged several limitations, including the relatively small sample size, which restricted analyses of associations between regional brain insulin responsiveness and cognitive outcomes. Additionally, insulin-induced cerebral blood flow responses provide an indirect measure of insulin-related neuronal activity and do not permit direct conclusions about neuronal insulin signaling. The study also lacked an energy- and macronutrient-matched control, and participants added peanuts to their habitual diets without prescribed food replacement. Consequently, the observed effects could partly reflect changes in overall dietary intake.
Although the findings suggest that longer-term peanut consumption may influence regional brain insulin responsiveness in older adults, particularly in memory-related regions, researchers could not determine whether these changes contributed to the previously reported improvements in verbal recognition memory.
"Daily consumption of 60 g of unsalted, skin-roasted peanuts for 16 weeks had a potentially beneficial effect on regional brain insulin responsiveness in older adults," wrote lead study author Lucia Kerkhof, PhD,of the Department of Nutrition and Movement Sciences at Maastricht University Medical Center, and colleagues.
Disclosures: The authors declared no conflicts of interest.
Source: Food & Function
