The human microbiome includes the genetic material of more than 100 trillion tiny microorganisms—fungi, yeast, bacteria, and even viruses, most of which hang out in our gastrointestinal tract to serve as guardians of our health. But when a healthy microbiome gives way to an imbalance—a “pathobiome”—any number of health problems can occur—from rheumatoid arthritis, to bacterial vaginosis.