Diets rich in whole grain (WG) cereals bring lower disease risks compared with refined grain-based diets. We investigated the effects of polished rice (PR), refined wheat (RW), unpolished rice (UPR), and whole wheat (WW) on short-chain fatty acids (SCFAs) and gut microbiota in ileal, cecal, and colonic digesta of normal rats. Animals fed with UPR and WW diets exhibited higher total SCFA in cecal and colonic digesta compared with those fed with PR and RW diets. Wheat diets contributed higher total SCFA than rice diets. In cecal and colonic digesta, animals fed with UPR and WW diets demonstrated higher acetate and butyrate contents than those given PR and RW. Firmicutes were the dominant eumycota in rat ileum digesta (>92% abundance). Cecal and colonic digesta were dominated by Firmicutes, Verrucomicrobia, and Bacteroidetes. UPR and WW affected gut microbiota, decreasing the proportion of Firmicutes to Bacteroidetes. SMB53, Lactobacillus, and Faecalibacterium were the main bacterial genera in ileal digesta. Akkermansia was highest in cecal and colonic digesta. In the colonic digesta of rats, the relative abundance of Akkermansia in rats on wheat diets was higher than that in rats on rice diets ( P < 0.05). Thus, UPR and WW could modulate gut microbiota composition and increase the SCFA concentration. Wheat diet was superior to rice diet in terms of intestinal microbiota adjustment.

Insoluble residue (INS) is a lignin-rich fraction of brewer's spent grain (BSG) that also contains β-glucan and arabinoxylan, the major constituents of dietary fiber. We investigated the effects of INS in diet-induced obese mice in terms of lipid metabolism and metabolic diseases. Male mice (C57bl6) were fed a high-fat diet (HFD), a HFD + 20% INS, a HFD + 20% cellulose (CEL), a HFD with a combination of 20% INS-CEL (1:1), or a control diet for 14 weeks. Insulin and glucose tolerance tests were performed after 12 weeks. Fasting plasma lipids, bile acid, and fecal bile acid were measured after 14 weeks of feeding, and tissues were collected for gene expression analysis. Body weight gain was significantly reduced with all fibers, but only INS and INS-CEL decreased fasting plasma low-density lipoprotein cholesterol and total cholesterol compared to HFD. CEL and INS-CEL significantly improved insulin resistance. Fecal bile acids were significantly increased by all fibers, but there was no change in plasma bile acid. Clostridium leptum was increased with all fibers, but universal bacterial diversity was only with INS and INS-CEL. In addition, INS significantly increased the abundance of Bacteriodes, while CEL decreased Atopobium and Lactobacillus. INS feeding significantly upregulated various genes of cholesterol and bile acid metabolism, such as Srebp2, Hmgcr, Ldlr, Cyp7a1, Pparα, Fxr, and Pxr, in the liver. INS, INS-CEL, and CEL significantly attenuated liver steatosis. Our results suggest that INS from BSG induced beneficial systemic changes in mice via gut microbiota, bile acids, and gene expression in the liver.