In a healthy body also lives a healthy intestine, one would like to say in reference to the Roman poet Juvenal. Because only when digestion functions optimally can the body be supplied with all important nutrients, vitamins and minerals. What is less well known is that the intestine also plays a central role in immune defense and performs about 70% of the tasks required for this. The basis of all this is an intact intestinal flora. The intestinal flora is an extremely complex ecosystem consisting of various bacteria and other single-celled organisms that colonize the intestine. The number of these unicellular organisms is almost one third higher than the number of cells in the human body. The living organisms of the intestinal flora are absolutely vital for us. They support digestion, help with immune defense and produce essential vitamins.