The importance of the gut-brain axis in maintaining homeostasis has long been appreciated. However, the past 15 yr have seen the emergence of the microbiota (the trillions of microorganisms within ...

The Microbiota-Gut-Brain Axis

The Impact of Dietary Fiber on Gut Microbiota in Host Health and Disease.

Ana M Valdes and colleagues discuss strategies for modulating the gut microbiota through diet and probiotics

https://www.bmj.com/content/bmj/361/bmj.k2179.full.pdf

Role of the gut microbiota in nutrition and health

The gut-liver axis in liver disease: Pathophysiological basis for therapy.

Evidence is accumulating that the gut microbiome is involved in the aetiology of obesity and obesity-related complications such as nonalcoholic fatty liver disease (NAFLD), insulin resistance and type 2 diabetes mellitus (T2DM). The gut microbiota is able to ferment indigestible carbohydrates (for example, dietary fibre), thereby yielding important metabolites such as short-chain fatty acids and succinate. Numerous animal studies and a handful of human studies suggest a beneficial role of these metabolites in the prevention and treatment of obesity and its comorbidities. Interestingly, the more distal colonic microbiota primarily ferments peptides and proteins, as availability of fermentable fibre, the major energy source for the microbiota, is limited here. This proteolytic fermentation yields mainly harmful products such as ammonia, phenols and branched-chain fatty acids, which might be detrimental for host gut and metabolic health. Therefore, a switch from proteolytic to saccharolytic fermentation could be of major interest for the prevention and/or treatment of metabolic diseases. This Review focuses on the role of products derived from microbial carbohydrate and protein fermentation in relation to obesity and obesity-associated insulin resistance, T2DM and NAFLD, and discusses the mechanisms involved.

Gut microbial metabolites in obesity, NAFLD and T2DM.

The gut microbiota benefits humans via short-chain fatty acid (SCFA) production from carbohydrate fermentation, and deficiency in SCFA production is associated with type 2 diabetes mellitus (T2DM). We conducted a randomized clinical study of specifically designed isoenergetic diets, together with fecal shotgun metagenomics, to show that a select group of SCFA-producing strains was promoted by dietary fibers and that most other potential producers were either diminished or unchanged in patients with T2DM. When the fiber-promoted SCFA producers were present in greater diversity and abundance, participants had better improvement in hemoglobin A1c levels, partly via increased glucagon-like peptide-1 production. Promotion of these positive responders diminished producers of metabolically detrimental compounds such as indole and hydrogen sulfide. Targeted restoration of these SCFA producers may present a novel ecological approach for managing T2DM.

http://science.sciencemag.org/content/sci/359/6380/1151.full.pdf

Gut bacteria selectively promoted by dietary fibers alleviate type 2 diabetes

Gnotobiotic mouse model is generally used to evaluate the efficacy of gut microbiota Sex differences of gut microbiota are acknowledged, yet the effect of recipient’s gender on the bacterial colonization remains unclear Here we inoculated male and female germ-free C57BL/6J mice with fecal bacteria from a man with short-term vegetarian and inulin-supplemented diet We sequenced bacterial 16S rRNA genes V3-V4 region from donor’s feces and recipient’s colonic content Shannon diversity index showed female recipients have higher bacteria diversity than males Weighted UniFrac principal coordinates analysis revealed the overall structures of male recipient’s gut microbiota were significantly separated from those of females, and closer to the donor Redundancy analysis identified 46 operational taxonomic units (OTUs) differed between the sexes The relative abundance of 13 OTUs were higher in males, such as Parabacteroides distasonis and Blautia faecis, while 33 OTUs were overrepresented in females, including Clostridium groups and Escherichia fergusonii/Shigella sonnei Moreover, the interactions of these differential OTUs were sexually distinct These findings demonstrated that the intestine of male and female mice preferred to accommodate microbiota differently Therefore, it is necessary to designate the gender of gnotobiotic mice for complete evaluation of modulatory effects of gut microbiota from human feces upon diseases

/pdf/sex-differences-in-colonization-of-gut-microbiota-from-a-man-28d8djnm72.pdf

Xing-peng Wang

Papers

Gut bacteria selectively promoted by dietary fibers alleviate type 2 diabetes

Sex differences in colonization of gut microbiota from a man with short-term vegetarian and inulin-supplemented diet in germ-free mice