A recent study involving overweight or obese older adults found that consuming 60 grams of a mixture of walnuts, pistachios, cashews, and hazelnuts daily for 16 weeks improved insulin sensitivity in five distinct regions of the brain. However, there were no significant changes in body weight, body composition, or peripheral insulin sensitivity. The research was published in the American Journal of Clinical Nutrition.
Insulin is a hormone produced by the pancreas that regulates blood sugar levels by facilitating the uptake of glucose into cells for energy production and storage. It helps cells in the body absorb glucose from the bloodstream to use for energy or store as glycogen in the liver and muscle tissues. When blood sugar levels rise, such as after eating, the pancreas releases insulin to help maintain a balanced and healthy sugar level.
Dysfunction in insulin production or its activity can lead to metabolic disorders such as diabetes, characterized by insufficient insulin production or ineffective use of insulin by the body. This dysfunction also extends to brain cells, known as brain insulin resistance, which can impair the function of neural cells and contribute to various neurological and mental health disorders, including Alzheimer’s disease, where it is associated with cognitive decline.
Study author Kevin MR Nijssen and his colleagues wanted to investigate whether a diet including various nuts would enhance brain insulin sensitivity in overweight or obese older adults. They highlighted that nuts are nutrient-rich foods, abundant in unsaturated fats and other bioactive compounds. Previous studies have shown that incorporating nuts into the diet lowers the risk of developing metabolic and cognitive disorders. The researchers designed an experiment to test this hypothesis.
The study involved 28 participants aged between 60 and 70 years, half of whom were female, all overweight or obese. The participants were divided into two groups. One group began by consuming 60 grams of unsalted, unroasted mixed nuts daily for 16 weeks, followed by an 8-week break, and then another 16 weeks without nut consumption. The second group followed the reverse order.
The researchers collected blood samples from the participants at the beginning, middle, and end of the intervention period to measure peripheral insulin sensitivity, lipid profiles, systemic inflammation, and levels of brain-derived neurotrophic factor (a protein essential for neuron survival and growth). Additionally, participants underwent magnetic resonance imaging and had their blood pressure measured throughout the study.
The results indicated no changes in the participants’ weight or body composition throughout the study. However, during the nut consumption phase, participants reduced their carbohydrate intake and slightly increased their fat intake.
Brain imaging analysis identified five clusters of brain cells that exhibited increased insulin sensitivity, located in the left and right occipital lobes and one cluster in the left frontal lobe. Peripheral insulin sensitivity remained unchanged.
The authors concluded, “The longer-term daily intake of mixed nuts for 16 weeks improved brain insulin action in occipital and frontal regions. Therefore, regional brain insulin resistance observed in older adults with overweight or obesity can be beneficially affected by intervention strategies, which may be important for the prevention of age-related metabolic diseases.”
The study highlights the potential dietary impacts on insulin resistance in the brain of overweight or obese older adults. However, it is important to note the small number of participants and the fact that the improved insulin sensitivity was confined to specific brain regions. Additionally, the study’s design does not clarify whether the observed effects were solely due to nut consumption or if they resulted from a reduction in other food intakes when nuts were included in the diet daily.
The paper, “Mixed nut consumption improves brain insulin sensitivity: a randomized, single-blinded, controlled, crossover trial in older adults with overweight or obesity”, was authored by Kevin MR Nijssen, Ronald P Mensink, Jogchum Plat, Dimo Ivanov, Hubert Preissl, and Peter J Joris.