The traditional view of Alzheimer's disease as simply a protein accumulation disorder is giving way to a more complex understanding that positions metabolic dysfunction at the disease's core. This paradigm shift suggests that how brain immune cells process energy may be as important as amyloid plaques themselves in determining cognitive fate. The research reveals that microglia, the brain's resident immune guardians, undergo profound metabolic rewiring when exposed to systemic stressors like insulin resistance and obesity. These cells switch their energy production pathways, shifting between glycolysis and oxidative phosphorylation in ways that compromise their ability to clear toxic proteins and maintain healthy synapses. Particularly significant is the discovery that this metabolic reprogramming creates a state of 'trained immunity' where microglia become chronically activated and destructive rather than protective. The blood-brain barrier emerges as another critical metabolic checkpoint, where impaired glucose transport and mitochondrial stress accelerate disease progression. Lipid metabolism plays a dual role, with APOE4 carriers showing distinctive microglial lipid accumulations that bridge genetic risk with inflammatory damage. The convergence points identified—including AMPK-mTOR signaling and inflammatory complexes like NLRP3—represent potentially druggable targets. Most promising are diabetes medications like GLP-1 receptor agonists, which appear to simultaneously address systemic metabolic dysfunction and brain-specific immune cell metabolism. This immunometabolic framework suggests Alzheimer's prevention and treatment may require addressing whole-body metabolic health rather than targeting brain pathology in isolation, potentially explaining why cardiovascular and diabetes interventions show cognitive benefits.