In this episode (the first of a two-part series) John and Mark review the emerging mechanisms that link lifestyle and environment with changes in the human microbiome. These changes are now known to alter visa our immune system, neurotransmitter dysfunction, the vagus nerve and neuroendocrine function e.g. PYY and GLP-1to alter brain inflammation and neurotransmitter communication. This is a foundation for depression, anxiety, altered cognition, etc.