The diverse ecology of the human gut microbiome is vital to human physiology. Numerous inflammatory-based chronic disorders, such as autoimmune and neurological diseases, are linked to changes in the microbiome. Chronic disorders, by definition, develop over longer time and require continued medical attention. This directly or indirectly reduces the quality of life of the affected individuals and possibly of their families and friends. The presence or imbalance of specific microorganisms (“who is there”) are not the only disease-related changes, however. High amounts of effector molecules produced by the microbiome, such as nucleic acids, (poly)peptides, and metabolites, are found in the gut. These molecules have thus far not been thoroughly studied. This information gap restricts the mechanistic understanding of the microbiome's functional impact on chronic disorders including Parkinson's disease and rheumatoid arthritis. The ExpoBiome project aims to, for the first time, comprehensively identify the components of this effector molecule complex and their effects on the human immune system. The project will develop and apply cutting-edge molecular approaches on microbiome samples taken from healthy people and those who have just been diagnosed with PD or RA. The resulting data will be integrated using existing and newly developed computational biology and machine learning approaches to put it into existing context and generate new insights on microbial factors in health and disease. A model clinical intervention (fasting) with the aim to reduce inflammation and thereby improving health will be applied and the resulting changes of the microbiome will be reviewed. Newly identified anti-inflammatory compounds will be specifically studied using a gut-on-chip model. ExpoBiome will thus lead to key advances to better understand how microbiome shifts provide benefits in the context of inflammatory-based chronic disordered, how specific molecules can be used to improve health, and to forecast treatment outcomes, thereby substantially contributing to the development of future diagnostic and therapeutic applications.