One study in the Journal of Clinical Gastroenterology concluded prebiotics and probiotics «serve to elicit changes in the gut microbiota composition that increase populations of purported beneficial gut bacterial genera.» (saragottfriedmd.com)
What's more, this association seems to be affected by changes in the gut microbiota caused by diet. (alivebynature.com)
After transferring fecal matter from one group of rodents to another, they observed similar changes in the gut microbiota, acetate levels, and insulin. (sciencedaily.com)