INS and Alzheimer disease: Dysbiosis of gut flora increases gut permeability so that microbial by-products and endotoxins enter the blood circulation, and consequently, systemic cytokines, microglial activation, and neuroinflammation are triggered; it forms bacterial amyloids that cross the BBB in order to initiate amyloid-beta aggregation; it decreases short-chain fatty acid production resulting in peripheral insulin resistance plus neuronal stress—these conditions combine to promote amyloid plaque formation as well as neurofibrillary tangle development alongside cognitive decline in AD.