Your belly may not be an obvious place to look for help with your mental health. But the makeup of your gut microbiome - the bacteria, fungi and other microbes lodging in your digestive system - can affect your mental state. Because of the rise of processed food, most of us have fewer types of gut microbes than our grandparents and great grandparents. And this is one of the reasons there is so much depression and anxiety in the world. You can improve stress, reduce anxiety and mitigate the effects of other mental health problems by tweaking the balance of bacteria in your belly - either by eating a diverse diet or ingesting appropriate amounts of “psychobiotics”.