Nutritional Immunometabolism

Over the last decades, inflammatory diseases such as type 1 and 2 diabetes, obesity, cancer or allergies have become prevalent particularly in western countries for partially understood reasons. Such a short period of time suggests that environmental factors in modern lifestyles contribute to this phenomenon. One of the biggest changes in modern lifestyle that accompanied industrialization is the reshaping of the nutritional landscape. While a traditional diet is notably high in dietary fiber and vitamins, western diet is characterized by its high content of saturated fats and highly digestible carbohydrates but low levels of fiber. Nutrients are not only a vital source of energy for the host but also for the trillions of bacteria that inhabit the intestinal tract. The presence and function of different gut bacteria is highly dependent on nutrient availability and subjected to high competitive pressure between different bacterial species. Thus, the western diet has been commonly associated with dysbiosis, the predominance of deleterious bacteria, while dietary fiber is a potent prebiotic favoring the growth of beneficial bacteria that process primary dietary metabolites into secondary metabolites, such as bile acids.

Gut bacteria tightly regulate the immune response through the release of primary metabolites that favor or impair immune cell function or secondary metabolites which are modified forms of factors such as bile acid. Dysbiosis has thus been commonly associated with disease development. On the other hand, immune cells also control bacterial populations, mostly through the release of immunoglobulin or indirectly by acting on the gut epithelium. The gut epithelium ensures the physical separation between host and gut microbiota but also dynamically affects both compartments. The notion of gut homeostasis encompasses a healthy microbiota and a functional epithelium and mucosal immunity. Disruption of gut homeostasis can not only lead to inflammation in the gut but also systemically contribute to diseases. More broadly, the tight interdependence nutrition, gut microbiota and host immunity means that disruption of one of these components will have dramatic impacts on host health.

The deorphanization of GPCR over the last 10 years has revolutionized the field. This led to the discovery of GPCR receptors for nutrients such as specific fatty acids and amino-acids and for bacterial metabolites has helped uncover the mechanisms underlying the effects of nutrition on immunity.

The recent appreciation of the central role of gut microbiota and gut homeostasis on health as well as the discovery of new nutrient sensing receptors impacting on immunity leaves this recent field with many unanswered questions. This Research Topic in nutritional immunometabolism will give the latest update to explain how western diet might be responsible for immune impairment and development of inflammatory diseases.