Human appetite is controlled by hormones secreted from various body sites that signal to neurons present in the hypothalamus. The gut microbiome can also influence appetite through its metabolites. Furthermore, lifestyle and environmental exposures can influence both appetite and the gut microbiome, about which little is known. The goal of this research is to demystify appetite regulation among children and adolescents by studying associations between appetite hormone levels, the gut microbiome and lifestyle and environmental exposures.