Gut microbiota have an effect on human health, but how they work is not known well enough. The behaviour of microbiota at protein level is studied at the University of Turku by means of metaproteomics. Previous studies have mainly focused on discovering the composition of microbiota, while there is still very little information about the behaviour of gut microbiota at protein level. Proteins perform most cell operations, and studying them in more detail may help us understand the interaction between cells and their environment. Metaproteomics is a good method for studying human gut microbiota, because it can identify and categorise the proteins involved.