In this episode, Kate Quilton and Tamal Ray investigate the subject of diet and gut bacteria. Tamal Ray looks into the benefits of bacteria on our mental health and takes a lesson in sauerkraut fermentation. Five volunteers who usually eat poor diets attempt to overhaul their gut bacteria by increasing their intake of fruit, vegetables, yogurt and cheese. And investigative journalist Morland Sanders finds out about the balloon pill, to see if it holds the answer to our obesity crisis.