The gut flora, or gut microbiota, consists of 1,000 types of bacteria, totaling some 40 trillion organisms. The latest research shows long-distance runners have large amounts of a certain type of gut bacteria, which leads to higher athletic ability and less fatigue. A bacterial imbalance was found to negatively affect sleep quality and the immune system. We look at the effect of gut microbiota on health with a researcher who aims to develop lifestyle plans tailored to each person's gut environment.