The number of microorganisms in human body is about 10 times as many as the number of cells, while the intestinal bacteria account for about 80% of the total number of microorganisms. Any “small trick” of intestinal bacteria may lead to great changes on human health. The intestinal bacteria not only affect the taste of your diet, but influence what kind of partner you choose. We have probably underestimated the role of intestinal bacteria. Starting from the world of microorganisms and integrating with the latest research results on intestinal bacteria, this book introduces the principles of how intestinal microorganisms affect people’s health. Actually, we are curious about the intestinal tract: Which is more important, gut brain or cerebrum? Is epityphlon a useless organ? How can intestinal bacteria affect our appetite? Readers can find answers to these questions in this book.