Fine-tuning of the mucosal barrier and metabolic systems using the diet-microbial metabolite axis

The human intestinal microbiota has profound effects on human physiology, including the development and maintenance of the host immune and metabolic systems. Under physiological conditions, the intestinal microbiota maintains a symbiotic relationship with the host. Abnormalities in the host-microbe relationship, however, have been implicated in multiple disorders such as inflammatory bowel diseases (IBDs), metabolic syndrome, and autoimmune diseases. There is a close correlation between dietary factors and the microbial composition in the gut. Long-term dietary habits influence the composition of the gut microbial community and consequently alter microbial metabolic activity. The diet-microbiota axis plays a vital role in the regulation of the host immune system, at least partly through altering microbial metabolism. In this review, we will describe the current findings regarding how dietary factors and microbial metabolites regulate the host immune system.