More than 100, 000 copies sold of the original edition in North America, and more than 4 million copies have sold world-wide in all languages.There have been many discoveries about the Gut-Brain since 2013 when Enders first wrote Gut (published in 2015). At the time much of the research was on animals, but since there are more than 20 reliable studies involving humans.Enders introduces psychobiotics, a term describing describes microbes that have psychological effects-and which may even be useful in treating conditions like depression and stress, and shows how our gut bacteria affect mood, stress levels, and depression.She also includes basic instructions for producing fermented vegetables - full of good gut bacteria - at home.