WASHINGTON, March 8 (Xinhua) -- Chinese scientists have identified a guild of particular gut bacteria that can ferment dietary fibers to help control blood glucose of patients with type 2 diabetes.
The study, published on Thursday in the journal Science, showed that a diversified high fiber diet can promote 15 strains of gut bacteria that produce short-chain fatty acids (SCFAs), which nourish gut epithelial cells, reduce inflammation, and play a role in appetite control.
Many gut bacteria have the genes and the capacity to produce SCFAs from carbohydrate fermentation. Deficiency of SCFAs are known to be associated with type 2 diabetes.
Zhao Liping and colleagues at Shanghai Jiao Tong University randomized patients to treatment or control group, both having similar intake of energy and macronutrients, using acrabose as the medication for blood glucose control but the treatment group had extra amount of diverse fibers.
Throughout the 12-week treatment, the intervention group, given a large, diversified amount of dietary fibers from whole grains, traditional Chinese medicinal foods and prebiotics, experienced more significant and faster improvement in blood glucose control, greater weight loss, and better lipid profile compared to the controls.
After taking the treatment diet for four weeks, patients had a new gut microbiota and kept the new gut microbiota for another 8 weeks. This group of bacteria reached greater abundance and diversity, and the patients had lower acetylated hemoglobin levels which indicated better blood glucose regulation.
The study also showed that these beneficial effects of the high fiber diet were directly contributed by changes in the gut microbiota by transplanting baseline and end of trial gut microbiota from the same individual to germfree mice.
"It provides compelling evidence supporting increased intake of dietary fibers may benefit T2D patients," Zhao told Xinhua Thursday.
Then researchers identified a small group of bacterial strains that were likely to be the key drivers of patients' clinical improvements: these bacteria out-competed others and became dominant members of the gut microbial community.
The study found their activity has increased the production of butyrate and acetate, two major beneficial sub-types of SCFAs that can promote the secretion of gut hormones that can increase insulin production, leading to improved blood glucose control.
They also help maintain a mildly acidic gut environment which is unfavorable for known detrimental bacteria.
Zhao's team found among 141 bacteria that can produce SCFA, only 15 are promoted by high fiber diet, 79 strains did not show changes in their population and 47 strains even reduced.
Genomic analysis showed that these 15 positive responders had more genes for utilizing plant fibers, producing more SCFAs from the same amount of fibers and were more tolerant to an acidified gut environment.
These 15 positive responders can be considered as a "guild" in ecological terms, belonging to three phyla. "They use the same class of environmental resources in a similar way," but they are a collection of very different bacteria, Zhao said.
In contrast, the 47 negative responders had more genes for utilizing animal carbohydrates derived from mucin in the gut, were less efficient to energy production from dietary fibers and has a lower tolerance to an acidified gut environment.
Among the reduced negative responders are bacteria that can produce toxic indole and hydrogen sulfite.
"We may target restoration of this guild of beneficial bacteria for better glycemic control in patients with type 2 diabetes. If you have lost most or all the members of the guild of these active SCFA producers, you may need a microbiota transplantation from a healthy donor whose microbiota profile best benefit you by providing those members missing in your gut," Zhao said.
The study showed that a dietary program that targets this beneficial guild of gut bacteria is a clinically effective "gut-specific" way to improve insulin secretion and therefore alleviates type 2 diabetes.
