People with type-2 diabetes who followed a diet containing a large variety of dietary fibres saw a larger drop in blood glucose levels after 12 weeks than the control group, found the researchers, led by Rutgers University, New Brunswick (RUNB).
The intervention diet included wholegrains, traditional Chinese medicinal foods rich in dietary fibres and prebiotics (WTP diet), while control patients received standard patient education and a diet of similar energy content and macronutrient composition.
The scientists also found that the proportion of participants who achieved adequate glycaemic control (glycated haemoglobin (HbA1c) < 7%) was significantly higher in the WTP group (89%) than in controls (50%).
Additionally, the high-fibre diet promoted a select group of bacterial strains that increased short-chain fatty acid (SCFA) production. The presence of these SCFA-promoting strains induced better glycaemic control, partially through increased glucagon-like peptide-1 (GLP-1) and fasting PYY peptide. Production of these two hormones is known to stimulate the production of insulin, effecting better glucose control.
“When the fibre-promoted SCFA producers were present in greater diversity and abundance, participants had better improvement in haemoglobin A1c levels, partly via increased glucagon-like peptide-1 production,” commented lead author Professor Liping Zhao, Department of Biochemistry and Microbiology, School of Environmental and Biological Sciences at RUNB.
Out of the 141 bacterial strains identified by the researchers as SCFA producers, only 15 were found to multiply in response to the high-fibre diet. Interestingly, not all strains from the same bacterial species were ‘positive responders’ to the diet, the scientists found. Although all these 15 strains were capable of producing the SCFA acetate, only five were butyrate producers.
Increased abundance of the ‘positive responder’ bacterial strains also reduced the amount of two harmful metabolites indole and hydrogen sulphide (H2S), the scientists observed. Indole production has previously been linked with defective tryptophan metabolism and impaired serotonin synthesis. H2S has been implicated in the development of Crohn’s Disease, ulcerative colitis and colorectal cancer.
High-fibre diets, which promote SCFA-producing strains of bacteria, could offer new strategies for treating type-2 diabetes and other conditions linked to microbiota imbalances.
The researchers propose that SCFA production from carbohydrate fermentation “can be considered an ‘ecosystem service’ provided by the gut microbiota to human host.”
“Targeted promotion of the active SCFA producers as ecosystem service providers via personalised nutrition may present a novel ecological approach for manipulating the gut microbiota to manage T2DM and potentially other dysbiosis-related diseases,” they added.
"Our study lays the foundation and opens the possibility that fibres targeting this group of gut bacteria could eventually become a major part of your diet and your treatment," concluded Zhao.
Volume 359, issue 6380, pp. 1151-1156, doi: 10.1126/science.aao5774
“Gut bacteria selectively promoted by dietary fibres alleviate type 2 diabetes”
Authors: Liping Zhao et al