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.