Psychologist Kimberley Wilson and Dr Xand van Tulleken take a journey around the human body, to find out what it can tell us about our innate capacity for change. In this episode, Kimberley and Xand are looking at our kidneys, and the enormous societal problems caused by this fist-sized organ. Together they bust some detoxing myths, hear about the dangers of the billion dollar illegal organ trade, and whether an artificial kidney might be on the way. Also - how many glasses of water do we really need in a day? Producer: Georgia Mills Researcher: Leonie Thomas Executive Producer: Robert Nicholson A Whistledown production for BBC Radio 4