The alleviation by wheat and oat dietary fiber alone or combined of T2DM symptoms in <i>db</i> / <i>db</i> mice

The effects of wheat and oat dietary fiber (DF) alone or combined on T2DM remain unclear. In this research, <i>db</i>/<i>db</i> diabetic mice were fed with diets containing 10% insoluble wheat dietary fiber (WDF), 10% insoluble oat dietary fiber (ODF), and 10% WODF (mixture of WDF and ODF, WDF : ODF = 1 : 1) for 8 weeks. The results showed that WDF, ODF, and WODF all reduced the body weight and fasting blood glucose (FBG) and improved oral glucose tolerance in <i>db</i>/<i>db</i> mice. WDF and ODF alone further relieved insulin resistance and decreased the levels of glycated hemoglobin A1c (GHbA1c), and glycosylated serum protein (GSP). In addition, WDF and ODF alone decreased the levels of TNF-α, IL-6, and IL-1β in serum. The colon function was improved and similar changes were observed in the gut microbiota structure and abundance in all the DF groups. The change of gut microbiota mainly manifested as reducing F/B ratio at the phylum level, while at the genus level as decreasing <i>Enterococcus</i>, <i>Escherichia</i>-<i>Shigella</i>, <i>Erysipelatoclostridium</i>, and <i>unclassified_f_Lachnospiraceae</i> and increase of <i>norank_f_Muribaculaceae</i>, <i>Bacteroides</i>, and <i>Alistipes</i>. Further testing of colonic bile acids (BAs) revealed that WDF, ODF, and WODF all significantly changed the composition of BAs, mainly reducing the levels of UDCA, HDCA, and 3β-UDCA. WODF further decreased DCA and increased β-MCA, LCA-3S, and 12-KCDCA. Importantly, WODF reduced the values of 12-OH-BAs/non-12-OH-BAs. Moreover, the TGR5 level was up-regulated in both the liver and colon, and the FXR level was up-regulated in the liver while down-regulated in the colon in all the DF groups. Furthermore, for the protein level, IRS-1, p-PI3K/PI3K, and AKT were up-regulated in the liver in all the DF groups, while for the mRNA expression level, GLUT4 was up-regulated, and FOXO1, GSK3β, PEPCK, and PGC-1α were down-regulated. WDF and WODF further up-regulated the mRNA expression levels of GYS and down-regulated that of G6Pase. These results suggested that WDF, ODF, and WODF all can alleviate T2DM through the gutmicrobiota-BAs-TGR5/FXR axis and liver IRS-1/PI3K/AKT pathway in <i>db</i>/<i>db</i> mice. WDF and ODF alone are beneficial for improving glucose metabolism and inflammation indicators, while WODF helps improve BAs' profile more in the colon.