Multiple studies have now confirmed a dramatic link between the health of our microbiome--the trillions of bacteria that live in our digestive tract--and our likelihood of getting devastating viral illnesses like COVID-19. But the good news is that our microbiome is constantly evolving, offering a pathway back to health. Dr. Robynne Chutkan explains this groundbreaking research and offers a prescriptive plan for anyone trying to rehab their gut microbes and restore their health, and gives practical advice for balancing both your internal and external environment by optimizing diet, exercise, sleep, and time outdoors to boost your host defenses and overall health.