“Darm mit Charme (‘Charming Bowels’) – which has sat atop the German paperback charts for the last eight weeks and shifted more than 200,000 copies in the process – may deal with defecation, constipation and other bowel movements, but its message is far from flippant: our gastrointestinal tract is not only the body’s most under-appreciated organ, but ‘the brain’s most important adviser’.”