Alzheimer's disease (AD) is a disorder which is today treated and approached at the crossroad of two medical specialties - psychiatry and neurology. The insidious onset which can often mimic depressive disorders or other type of psychiatric disorders, the behavioral changes, the paranoid thoughts usually send people to the psychiatrist, while the brain changes observed on magnetic resonance imaging (MRI) scans and other imaging techniques may indicate the need for neurological monitoring also. The complex symptomatology and progression of this dementia requires a multidisciplinary approach and recent studies focused on adding a third perspective: a metabolic one. The common findings regarding type 2 diabetes and AD made some researchers to informally name it "the third type diabetes". This mini review aims to highlight the mechanisms through which brain insulin resistance can lead to cognitive impairment and to make a short overview of the current findings which demonstrate why insulin may be a promising adjunctive treatment of Alzheimer's dementia, for certain patients.