The fact that our health begins in the gut has been known for thousands of years. Today it is clear that our intestines are more than just a "digestive tube", as this important organ fulfils a variety of other functions. For example, a disturbance of gut health is directly related to the development of chronic diseases. The intestinal flora, i.e. the microbial colonization of the intestinal mucosa, plays a particularly important role in this process. The intestinal flora is also known as the 'intestinal microbiota'. It is the most important part of our immune system and thus offers us effective protection against infection.