Background: In recent years, especially after the development of sophisticated metagenomic studies, research on the intestinal microbiota has increased, radically transforming our knowledge about the microbiome and its association with health maintenance and disease development in humans. Increasing evidence has shown that a permanent alteration in microbiota composition or function (dysbiosis) can alter immune responses, metabolism, intestinal permeability, and digestive motility, thereby promoting a proinflammatory state. Such alterations can mainly impair the host's immune and metabolic functions, thus favoring the onset of diseases such as diabetes, obesity, digestive, neurological, autoimmune, and neoplastic diseases. This comprehensive review is a compilation of the available literature on the formation of the complex intestinal ecosystem and its impact on the incidence of diseases such as obesity, non-alcoholic steatohepatitis, irritable bowel syndrome, inflammatory bowel disease, celiac disease, and digestive neoplasms.
Conclusion:: Alterations in the composition and function of the gastrointestinal microbiota (dysbiosis) have a direct impact on human health and seem to have an important role in the pathogenesis of several gastrointestinal diseases, whether inflammatory, metabolic, or neoplastic ones.