INS and Alzheimer disease: The complex mechanisms that might modulate the connection between the gut microbiome and AD were summarized by Kohler et al., in whose model there is increased translocation due to a leaky gut (either caused by aging or environmental factors) of Gram-negative bacteria, lipopolysaccharide fragments that lead to the production of ROS, toxic catabolites from bacteria, increased levels of quinolinic acid, changes in energy metabolism, and insulin resistance, and there are reduced levels of short chain fatty acids, so the astrocyte–neuron glutamate–glutamine shuttle is impaired [54].