The concept that the gut is central to human health is fundamental to Ayurvedic medicine, traditional Chinese medicine, and Hippocratic medicine. Almost 2,500 years ago, the ancient Greek physician Hippocrates said that "all disease begins in the gut" The gut’s importance became increasingly recognized in the early 2000s, prompted by a reduction in sequencing prices and a range of computational advances that allowed scientists to assemble an initial picture of microbial diversity within the gut. Discoveries surrounding the gut microbiome’s relationship to a variety of diseases soon arose, with links found to type 2 diabetes, obesity, cardio-metabolic diseases, and neurodegenerative...