I am taking a break over the holidays. For the next four weeks, I will be republishing a few of my favourite blogs. We have always known that our mood affects our guts. My anxious patients complain of diarrhoea and my depressed patients of constipation. I could never have imagined how much of a role the gut microbiota plays in communicating with the brain and modulating behavior. I never took “gut feeling” literally! Our gut, the small intestine and the large intestine, is filled with over a kilogram of bacteria, the gut microbiota. That’s almost the weight of an average…