Microbiome and diseases: Metabolic disorders

Following the work of pioneers at the beginning of the twentieth century and later in the 1960s, there is nowadays a renewed interest for the impact of gut microbial communities on host metabolism. Nonetheless, we still ignore the real contribution of the intestinal microbiota to our energy homeostasis. The obesity pandemic is due to unbalanced energy intake (too high) vs. expenditure (too low) and not to the colonization of our intestine by unfavorable microbes. Nonetheless, gut microorganisms and in particular bacteria can metabolize a variety of dietary compounds, thereby releasing bioactive molecules that can influence metabolic functions of the host. Intestinal bacteria can also influence immune responses, which are known to play a role in the development of chronic metabolic disorders. Moreover, the approach of transferring gut microbial communities via fecal transplantation to germfree animals or human subjects has demonstrated the causal role of intestinal microbes in regulating host energy homeostasis and the development of metabolic pathologies. Experimental studies have even identified single cultured bacteria that influence metabolic responses, including underlying molecular mechanisms and bioactive molecules. All these findings speak in favor of the importance of the gut microbiota for host metabolism. In the present chapter, we summarize data in a critical manner and discuss key notions pertaining to the impact of gut microbial communities on host metabolism and ensuing implications for the development of metabolic disorders.