Unsaturated fatty acids derived from dietary lipids were found to be saturated by gut microbes. By analyzing this newly discovered saturating metabolic system, we identified hydroxy fatty acids, oxo fatty acids, partially saturated fatty acids, and conjugated fatty acids as metabolic intermediates, and confirmed the existence of these fatty acids in host tissues. We evaluated the physiological function of these newly found fatty acid metabolites and found that hydroxy fatty acids, which are initial metabolic products, contribute to recovery from damage to the intestinal epithelial barrier. Furthermore, hydroxy fatty acids and oxo fatty acids were found to control fatty acid metabolisms by regulating PPARs and LXR, nuclear receptors. These results suggested that fatty acid molecular species formed specifically in the intestinal tract by gut microbial fatty acid metabolism can influence the health of the host. It might be possible to enhance health and prevent lifestyle-related diseases by controlling the composition of intestinal microbiota and the fatty acid composition of dietary lipids via generation of novel functional fatty acids in intestine. This review summarizes overview of gut microbial fatty acid metabolisms, functional analysis of the fatty acid metabolites, and process development for novel functional fatty acid production by applying the function of lactic acid bacteria.

The enterobacteria biotransform bile acids as well as vitamins and short-chain fatty acids. Enterobacteria-mediated bile acid biotransformation causes the alteration of intestinal bile acid composition resulting in the regulation of host bile acid metabolism through nuclear receptor farnesoid X receptor (FXR) and protein degradation signaling. Recently, it has been reported that enterobacteria-mediated bile acid signaling is a target for the prevention of obesity. In this article, I would like to introduce the involvement of enterobacteria-mediated bile acid signaling in lipid homeostasis.