Human gut microbiota comprises trillions of microbes—bacteria, viruses and fungi—that reside within the digestive tract. But what do we really know about those communities’ connection to specific health conditions and outcomes? Researchers have known for a while about the “gut-brain axis,” a complex network that links intestinal function to the emotional and cognitive centers of the brain. So it makes sense that scientists are exploring a slew of gut axes that highlight the connections or pathways between the microbiome of the gut and other major body systems such as the lungs, immune system and skin. Supplement solutions so far include prebiotic fiber, strain-specific probiotics, combination synbiotics, and even metabolite-rich postbiotics that don’t contain live microorganisms.