The Field at a Glance The human gut contains trillions of microorganisms—bacteria, fungi, viruses, and archaea—that influence digestion, immunity, metabolism, and neurological function. Metagenomic studies estimate the collective genes of our gut microbiome outnumber human genes by 100 to 150 times. Roughly 70-80% of the body’s immune cells reside in gut-associated lymphoid tissue, making the…