Bound Phenolics Ensure the Antihyperglycemic Effect of Rice Bran Dietary Fiber in db/db Mice via Activating the Insulin Signaling Pathway in Skeletal Muscle and Altering Gut Microbiota

Whole-grain dietary fiber intake is beneficial in the prevention of metabolic syndrome. Considering rich in bound phenolics being a special characteristic of whole-grain dietary fiber, the aim of this study was to evaluate the effects of the presence or absence of bound phenolics in rice bran dietary fiber (RBDF) on regulating glucose metabolism in diabetic db/db mice. In comparison to phenolics-removed RBDF (PR-RBDF) intervention without an antihyperglycemic effect, RBDF and formulated RBDF (F-RBDF, obtained by mixing PR-RBDF and hydrolyzed-bound phenolics) significantly reduced fasting blood glucose levels after 1 and 5 weeks of interventions, respectively. The presence of bound phenolics interventions could activate the IRS1/AKT/GLUT4 insulin signaling pathway in skeletal muscle and alter gut microbiota by modulating gut microbiota dysbiosis and enriching the butyric-acid-producing bacteria genera of the families Lachnospiraceae and Ruminococcaceae, thus leading to the reduction of blood glucose levels. These findings indicate that bound phenolics ensure the antihyperglycemic effect of RBDF.