Over the last two decades, it has become clear that the human gut microbiota, a complex community of bacteria, archaea, fungi and viruses, are a critical determinant of human health and disease. Microbiota-derived metabolites provide the host with energy, protect against pathogens, modulate immune and endocrine systems as well as the level of reactive oxygen species in the gut. It has come with no surprise that the human gut microbiota is also linked to the production, utilisation and regulation of host hormones. This implies that the gut microbiota is capable of influencing human behaviour, appetite regulation and metabolism as well as development and immunity. Many of the advances in the field of crosstalk between the gut microbiota and host health, disease and behaviours are generally based on DNA analyses of microbial populations and transplantation of monocultured commensal species to germ-free animals. Recent reports on the activity of the gut microbiota in gastrointestinal disea