The gut is a major organ for the production of immune responses and is colonized by a large variety of microbes. The composition of microbes in the gut influences immune responses qualitatively and quantitatively and is also observationally correlated with enteric and extra-intestinal infectious and non-infectious diseases. Animal models have been extremely useful to unravel the relationships of the gut microbiome with immune responses and various diseases.

The multiple findings of correlations of gut microbiome composition with immune responsiveness and disease entities have motivated the search for causal relationships, and a review of work carried out with this aim is the main objective of this report. It was found that the host’s diet is a key variable in shaping the composition of the gut microbiome. In turn, microbiome metabolites may affect various host functions, such as glucose and lipid metabolism and the cardiovascular system.

Fecal microbiome transplantation (FMT) has been instrumental in exploring the pathogenesis of enteric diseases. Probiotic bacteria have the potential to increase immune responses and to ameliorate metabolic diseases.

Gut microbiome; Host immune responses; Enteric disease; Extra-intestinal disease; Type 2 diabetes mellitus; Obesity; Diet of host; Fecal microbiome transplantation; Probiotic bacteria; Diet as health promoter