Obesity and diabetes are increasing worldwide, with serious medical and socio-economic consequences. Both are diseases that are caused and influenced by a variety of both genetic and environmental factors. Another common feature is the development of persistent inflammatory processes, suggesting that metabolic disorders affect the immune system. The human intestinal flora, especially the metabolic products it produces, appear to play an important role in the development of obesity and diabetes. However, the underlying mechanisms are still unclear. In our project, we want to use new methods (gnotobiotics, metagenomics and metabolomics) to investigate the complex interrelationship between the gut flora, metabolism and immune function in order to understand how these factors contribute to the development of obesity and diabetes. In doing so, we aim to lay the foundation for new innovative strategies to prevent and treat these important diseases.