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High intake of dietary fibers was found to be inversely associated with type-2 diabetes (T2D), whereas the difference among different dietary fibers on T2D remains unclear. Therefore, we have investigated the effects of different dietary fibers on T2D. Nine types of dietary fibers were used to investigate and evaluate their effects on type-2 diabetic rats via physiology, genomics, and metabolomics. We found that supplementation with β-glucan, arabinogalactan, guar gum, apple pectin, glucomannan, and arabinoxylan significantly reduced the fasting blood glucose, whereas carrageenan, xylan, and xanthan gum did not affect glycemic control in diabetic rats. Also, bioactive dietary fibers (β-glucan, arabinogalactan, guar gum, and apple pectin) associated with the increased butyric acid level and abundance of beneficial bacteria (Lachnobacterium, Parabacteroides, Faecalibacterium, Akkermansia, and some butyric acid-producing bacteria), as well as improved host metabolism by decreasing 12α-hydroxylated bile acids, acylcarnitines, and amino acids (leucine, phenylalanine, citrulline, etc.), thereby exert beneficial effects on T2D. It was also found that β-glucan might attenuate insulin resistance via downregulation of Prevotella copri-mediated biosynthesis of branched-chain amino acids in T2D. Together, our study uncovered the effects of different dietary fibers on T2D, along with their potential mechanism.

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The occurrence and development of insulin resistance (IR) are usually related to the change of gut microbiota. Our previous study showed that arabinogalactan (AG) could selectively increase the relative abundance of Bifidobacterium longum and Faecalibacterium prausnitzii in in vitro fermentation. However, their effect on IR remains unclear. In the current study, we investigated the effects of AG, B. longum, F. prausnitzii and their combinations on insulin-resistant mice. Intake of AG and those two strains reduced the body weight, fat accumulation, and homeostasis model assessment of IR of the mice with IR, and decreased the level of serum glucose, insulin, and lipids. Meanwhile, they could alleviate the injury of the liver. Moreover, AG, B. longum, and F. prausnitzii regulated the production of short-chain fatty acids and elevated the abundance of gut probiotics such as Lactobacillus, Lactococcus, and Bifidobacterium. However, the effect of giving only AG or a single strain was weaker than the combination of AG, B. longum, and F. prausnitzii. Our study attempted to find a new way to prevent the development of type 2 diabetes in the early stage and provided evidence for new therapy against IR with a combination of prebiotics and two bacterial strains of gut origin.

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The interaction between gut microbiota and polysaccharide is being paid more and more attention. Galactan is a kind of polysaccharide mainly composed of galactose, and it has been shown to play a significant role in regulating gut microbiota. Bacteroides thetaiotaomicron is considered as the best degrader of polysaccharides. The purpose of this paper was to investigate the utilization of four different galactans, including agarose, carrageenan, arabinogalactan, and glucofucogalactan, by our own isolated B. thetaiotaomicron A4. Samples of cultures grown on either four galactans groups or control groups were collected. The change of OD600, pH, and short‐chain fatty acids (SCFAs) during fermentation were determined, and growth curve and transcriptome of B. thetaiotaomicron A4 were studied. B. thetaiotaomicron A4 could utilize the four galactans and grew well on them, with carrageenan being most utilized, followed by arabinogalactan, glucofucogalactan, and agarose. SCFAs (mainly acetic acid and propionic acid) produced along with the decreased pH during fermentation. A large number of genes of B. thetaiotaomicron A4 were upregulated and functioned in different pathways during the degradation of the four galactans. The carbohydrate metabolism‐related pathways of B. thetaiotaomicron A4 were enriched after feeding the four galactans, although the specific pathways were different among four galactans groups. The different structural characteristics of four galactans required that B. thetaiotaomicron A4 could excrete corresponding enzymes to degrade them. These results help to understand the interaction between galactans and gut microbe.