It is now well documented that changes in gut microbiota composition accompany obesity and type 2 diabetes (T2D) and contribute to low-grade inflammation, insulin resistance,and glucose intolerance. It is not yet clear if T2D predisposes the intestine to allow more microbial products or possibly live bacteria to subvert the gut mucosal barrier. However, it is known that hyperglycemia during T2D induces a more permissive gut barrier allowing increased penetration of microbes and their products into the blood. An important next step is to determine which strains of bacteria promote dysbiosis, allowing bacteria or bacterial components to subvert the gut barrier and alter glucose control. It is hypothesized that gut microbes in the colon and other lower gut segments are key modulators of energy balance, glucose homeostasis and insulin sensitivity.