Up to one-third of adults in the U.S. will be affected by an anxiety disorder in their lifetime. Prebiotics—compounds that influence the host gut microbiome—hold promise to be preventive, more accessible, inexpensive, and associated with fewer adverse effects than common pharmacologic or behavioral interventions. The GUT-FEELINGS project will identify non-pharmacological microbiome-modulating interventions that target the gut-brain axis to decrease symptoms of stress and anxiety. This project will bring together emerging technologies involving microbiome modulators, large-scale decentralized clinical trials, and the synergy of concurrently collected patient-reported, digital, and objective data.