Although the brain and the body have always been viewed as separate entities – treated in separate hospitals – science now shows that they are intimately linked. Startlingly, we now know that our immune system is in constant communication with our brain and can directly alter our mental health. This has opened up a new frontier in medicine. Could inflammation cause depression, and arthritis drugs cure it? Can gut microbes shape your behaviour through the vagus nerve? In this book, Dr Monty Lyman explores the fascinating connection between the mind, immune system and microbiome, offering practical advice on how to stay healthy. A specialist in the cutting-edge field of immunopsychiatry, Lyman argues that we need to change the way we treat disease and the way we see ourselves. For the first time, we have a new approach to medicine that treats the whole human being.