Eating mixed nuts improves brain insulin sensitivity Original paper

In this randomized crossover trial, consuming 60 grams of mixed nuts per day improved brain insulin sensitivity and some cardiometabolic risk factors in adults with overweight or obesity.

The effects of mixed nut consumption on brain blood flow (the primary outcome).

Other outcomes included brain insulin sensitivity, peripheral insulin sensitivity, blood lipids (i.e., total cholesterol, HDL-C, LDL-C, triglycerides), blood pressure, and liver fat.

28 adults (ages 60–70; 14 men and 14 women) who had overweight or obesity (a BMI between 25 and 35).

In this 16-week randomized crossover study, the participants underwent two conditions: one in which they consumed 60 grams of nuts per day (15 grams each of walnuts, cashews, hazelnuts, and pistachios) and one in which they consumed no nuts (the control condition). There was an 8-week washout period between each condition.

During both conditions, the participants were instructed to avoid consuming foods rich in omega-3 fatty acids, including other nuts, seeds, and fish oil capsules, and to follow the Dutch food-based dietary guidelines.^[1]

Peripheral insulin sensitivity was assessed by measuring the glucose and insulin responses to a 2-hour oral glucose tolerance test. Brain insulin sensitivity was assessed via magnetic resonance imaging (MRI) by measuring changes in cerebral blood flow (CBF) after the intranasal (via the nose) administration of insulin.

A total of 6 different brain clusters showed a lower CBF response to insulin (indicating improved brain insulin sensitivity) after the mixed nut condition, compared with the control condition.

In contrast, peripheral insulin sensitivity did not differ between the conditions. There was also no difference for brain-derived neurotrophic factor (BDNF) or C-reactive protein (CRP) levels.

Compared to the control condition, mixed nut consumption reduced total cholesterol (−0.27 mmol/L or −10.44 mg/dL), LDL cholesterol (−0.24 mmol/L or −9.28 mg/dL), office (but not 24-hour ambulatory) systolic blood pressure, and liver fat.

Five of the 6 clusters where improved brain insulin sensitivity was observed are mainly located in the occipital lobe: the left lateral occipital cortex, the occipital pole, and the superior parietal lobule; the left lateral occipital cortex; the left lingual gyrus and precuneus cortex; the right cuneal cortex, occipital pole, and supracalcarine cortex; and the right lateral occipital cortex. A final cluster was located in the frontal lobe: the left precentral, postcentral, and middle frontal gyrus. The occipital regions are part of the default mode network, which modulates metabolic processes that are essential for reward processing and food-related cues and eating behavior.^[2][3]