Brain Insulin-sensitivity

Primary aim of the study is to assess the effect of 12-week daily avocado consumption on cerebral blood flow and markers of cardio- and vascular health in both, the periphery and the brain, in pre-diabetic individuals with overweight or obesity. Secondary objective is to assess the effects of 12-week daily avocado consumption on brain insulin sensitivity after intranasal insulin delivery, vascular function, markers of metabolic health, cognition, and psychological well-being. For that purpose a total of 34 men and women between the ages of 40-75 years old, will participate in a randomised crossover intervention study.

Rationale: Healthy foods, including mixed nuts, may improve brain function, which is essential for cognitive and metabolic health, and may contribute to improved food intake regulation. It is therefore important to investigate the specific effects of walnuts on cerebral blood flow responses before and after intranasal insulin administration, as well as their associated functional benefits. The investigators hypothesize that long-term walnut consumption improves vascular function and insulin-sensitivity in the brain, thereby enhancing cognitive performance and appetite control in abdominally obese men and women. Objective: The primary objectives are to investigate in abdominally obese adults the effects of 24-week walnut consumption on (regional) vascular function and insulin-sensitivity in the brain, while the investigators will also assess changes in cognitive performance and appetite-related brain reward activity (secondary objectives). Cerebral blood flow responses before (brain vascular function) and after the administration of intranasal insulin spray (brain insulin-sensitivity) will be quantified by the non-invasive gold standard magnetic resonance imaging (MRI)-perfusion method Arterial Spin Labeling (ASL). Study design: This intervention study will have a randomized, controlled parallel design. The total study duration will be 24 weeks. Study population: Fifty-five abdominally obese men and (postmenopausal) women (aged 45-75 years) without a history of cardiovascular diseases or complaints will participate. This study population is expected to have a decreased cerebral blood flow at baseline and are also at increased risk of cognitive impairment, allowing for improvement by the intervention. Intervention: Study participants will receive daily 50 g (about 15% of energy) of raw walnuts (walnut intervention) or no walnuts (control intervention) for 24 weeks. Main study parameters/endpoints: At baseline and after 24 weeks (follow-up), participants will visit the research facilities for assessments. The primary endpoint is the difference in the cerebral blood flow response before and after intranasal insulin administration between the walnut and control intervention. Cognitive performance will be assessed, while the investigators will also focus on appetite-related brain reward activity (secondary outcomes).

This study aimed at helping researchers understand how a medication called haloperidol can affect insulin action in the brain. Insulin is a hormone in the body that controls sugar levels in part by lowering the amount of glucose produced by the liver. After eating a meal, insulin levels go up in both the blood and the brain. Insulin in the brain has also been shown to affect the way the brain works and processes information (also known as "cognition"). Haloperidol, is an antipsychotic medication used to treat a variety of disorders such as schizophrenia spectrum disorders, bipolar disorder, and major depressive disorder, but long-term use can have metabolic side effects, like weight gain, type 2 diabetes, and cardiovascular disease. The purpose of this study is to investigate how antipsychotic medications, such as haloperidol, which carries the risk of metabolic changes, might interrupt the effect of insulin action in the brain. This will help researchers learn how to potentially reduce metabolic risk for people who take these kinds of medications in the future.

Disturbances in brain insulin sensitivity are associated not only with obesity and type 2 diabetes, but also with brain aging and cognitive decline. Longitudinal studies suggest that dietary patterns, particularly those high in dairy intake, may impact brain function via the gut-brain axis. Indeed, dairy foods are known to modulate gut microbiota and may, through this pathway, not only improve brain insulin sensitivity and cognitive performance, but also mental health and appetite regulation. However, underlying mechanisms remain largely unexplored. The primary objective of this study is to evaluate, in older adults with overweight or obesity, the effects of a high-dairy food pattern (4-5 daily servings of (butter)milk, cheese, yogurt, or cottage cheese) compared to a low-dairy food pattern (≤1 serving daily) on (regional) brain vascular function and insulin sensitivity. These outcomes will be quantified using the non-invasive MRI perfusion technique Arterial Spin Labeling (ASL), which assesses cerebral blood flow (CBF) in response to intranasal insulin, a validated physiological marker of brain insulin sensitivity. Secondary objectives include changes in cognitive performance (via the CANTAB neuropsychological test battery), gut microbiota composition (via shotgun metagenomic analysis of fecal samples), and appetite-related brain reward activity (via BOLD-fMRI with food cues). Exploratory analyses include conventional cardiometabolic risk markers (blood pressure, lipid and glucose metabolism), and perceivable (consumer) benefits.

Impaired brain vascular function precedes the development of reduced cognitive performance, while brain insulin-resistance is associated with cognitive decline. Evidence from epidemiological studies has already suggested beneficial effects of wild blueberry consumption on cognitive performance. However, underlying mechanisms have not yet been established, while well-controlled trials on longer-term effects of wild blueberries on cognitive performance are highly needed. This study hypothesizes that longer-term wild blueberry intake improves (regional) brain vascular function and insulin-sensitivity, thereby improving cognitive performance in older men and women. The primary objectives are to investigate in older adults the effect wild blueberry consumption on (regional) vascular function and insulin-sensitivity in the brain, and to focus on changes in cognitive performance as assessed with the CANTAB neuropsychological test battery (i.e., secondary objective). Cerebral blood flow responses before (brain vascular function) and after the administration of intranasal insulin spray (brain insulin-sensitivity) will be non-invasively quantified by the non-invasive gold standard magnetic resonance imaging (MRI)- perfusion method Arterial Spin Labeling (ASL).

Protein-rich foods may improve brain insulin-sensitivity, which is important for cognitive and metabolic health, and may also translate into an improved food intake regulation. It is therefore pertinent to delineate the effects of plant-derived proteins, which are a more sustainable alternative to animal-derived proteins, on brain insulin-sensitivity and related functional benefits. The hypothesis is that daily plant-derived or animal-derived protein supplementation improves brain vascular function and insulin-sensitivity, thereby improving cognitive performance and appetite control in overweight or obese older men and women. The primary objective is to investigate in overweight or obese older adults the effect of daily protein supplementation for two weeks with either a plant-derived protein or an animal-derived protein on vascular function and insulin-sensitivity in the brain, while changes in cognitive performance and appetite-related brain reward activity will also be evaluated (secondary study objectives). Cerebral blood flow responses before (brain vascular function) and after the administration of intranasal insulin spray (brain insulin-sensitivity) will be quantified by the gold standard magnetic resonance imaging (MRI)-perfusion method Arterial Spin Labeling (ASL).