Richard Sprague is a veteran technologist from Apple and Microsoft who has done over 600 microbiome tests using skin, nose, and fecal samples over the last six years. His fascination with his gut microbiome has led him to start Personal Science, a personalized nutrition project to help people discover their ideal diet by helping them track their glucose responses to doctor-prescribed meals. We speak with him about the future of gut microbiome testing and personalized diets that are projected to become a $64bn market in the next two decades.