3-(4-Hydroxy-3-methoxyphenyl)propionic Acid Produced from 4-Hydroxy-3-methoxycinnamic Acid by Gut Microbiota Improves Host Metabolic Condition in Diet-Induced Obese Mice

4-Hydroxy-3-methoxycinnamic acid (HMCA), a hydroxycinnamic acid derivative, is abundant in fruits and vegetables, including oranges, carrots, rice bran, and coffee beans. Several beneficial effects of HMCA have been reported, including improvement of metabolic abnormalities in animal models and human studies. However, its mitigating effects on high-fat diet (HFD)-induced obesity, and the mechanism underlying these effects, remain to be elucidated. In this study, we demonstrated that dietary HMCA was efficacious against HFD-induced weight gain and hepatic steatosis, and that it improved insulin sensitivity. These metabolic benefits of HMCA were ascribable to 3-(4-hydroxy-3-methoxyphenyl)propionic acid (HMPA) produced by gut microbiota. Moreover, conversion of HMCA into HMPA was attributable to a wide variety of microbes belonging to the phylum Bacteroidetes. We further showed that HMPA modulated gut microbes associated with host metabolic homeostasis by increasing the abundance of organisms belonging to the phylum Bacteroidetes and reducing the abundance of the phylum Firmicutes. Collectively, these results suggest that HMPA derived from HMCA is metabolically beneficial, and regulates hepatic lipid metabolism, insulin sensitivity, and the gut microbial community. Our results provide insights for the development of functional foods and preventive medicines, based on the microbiota of the intestinal environment, for the prevention of metabolic disorders.