Dietary fiber promotes beneficial gut bacteria in type 2 diabetes

Last Updated: 2018-03-14

By Will Boggs MD

NEW YORK (Reuters Health) - Dietary fiber promotes a select group of short-chain fatty acid (SCFA)-producing gut bacteria that are associated with improvement in hemoglobin A1c levels in patients with type 2 diabetes, researchers reported March 9 in Science.

"The most surprising finding was that only a selective group of fiber-fermenting bacteria was actually promoted by the increased amount of highly diverse fibers," Dr. Liping Zhao from Rutgers University in New Brunswick, New Jersey, and Shanghai Jiao Tong University in China told Reuters Health by email. "Out of the 141 bacterial strains which were genetically capable of using fibers to produce short-chain fatty acids, only 15 became predominant after consuming the high-fiber diet, 79 remained unchanged, and 47 even declined as compared to baseline."

Gut bacteria produce SCFAs through bacterial fermentation of non-digestible carbohydrates, and these SCFAs provide an energy substrate to colonocytes, reduce inflammation and regulate satiety. Deficient SCFA production has been associated with type 2 diabetes and other diseases.

Dr. Zhao and colleagues randomized 27 patients with clinically diagnosed type 2 diabetes to receive a high-fiber diet composed of Whole grains, Traditional Chinese medicinal foods and Prebiotics (the WTP group) and 16 similar patients to receive usual care.

Hemoglobin A1c, the primary outcome measure, decreased significantly in both groups, but there was a greater reduction in the WTP group from day 28 onward, and significantly more patients in the WTP group (24/27, 89%) than in the control group (8/16, 50%) achieved hemoglobin A1c levels below 7%.

In mice that received postintervention microbiota from the two groups, fasting and postprandial blood glucose levels were lower in those that received WTP microbiota than in those that received control microbiota, the researchers report.

The team went on to identify differences in gene richness, which tended to be higher in the WTP group than in the control group after day 28 and was associated with better clinical outcomes in the WTP group.

They also identified a group of acetate- and butyrate-producing bacterial strains that were selectively promoted by the dietary intervention.

"These positive responders are likely the key players for maintaining the mutualistic relationship between the gut microbiota and the human host," the authors suggest. "Promoting this active group of SCFA producers not only enhanced a beneficial function but also maintained a gut environment that keeps detrimental bacteria at bay."

"In ecological terms, the production of SCFAs from carbohydrate fermentation, which is needed to maintain human health, can be considered an 'ecosystem service' provided by the gut microbiota to human hosts," they conclude. "Restoring or enhancing the lost or deficient function by reestablishing the functionally active ecological populations as ecosystem service providers (ESPs) is the key to a healthier microbiota, which can help alleviate disease phenotypes.

"Patients with type 2 diabetes may benefit from promoting a selective group of gut bacteria that produce short-chain fatty acids," Dr. Zhao said. "Increasing dietary fiber intake may be a new nutritional approach to manage type 2 diabetes. Different patients may need their own personally tailored nutritional plan to encourage the growth of such key bacteria."

Dr. Martin Weickert from Centre of Applied Biological and Exercise Sciences at Coventry University, in the U.K., who recently reviewed the impact of dietary fiber consumption on insulin resistance and the prevention of type 2 diabetes, told Reuters Health by email, "If lack of fermentation would indeed be crucial for increasing risk of type 2 diabetes, why do large prospective cohort studies consistently indicate that virtually non-fermentable cereal fibers (in U.S. studies: wheat bran) appear to be protective, whereas fermentable fibers derived from fruit and vegetables are not?"

"Virtually all published studies indicate that high intake of cereal fibers and whole grain appear to reduce diabetes risk by 20-30%, with no proven effect that fermentable fibers have similar beneficial effects," he said. "Therefore, other mechanisms why (non-fermentable) cereal fiber intake protects from diabetes appear to be involved."

These mechanisms could include "fiber-related inhibition of the absorption of dietary protein (according to our work), thereby preventing activation of the mTOR/S6K1 signaling cascade which is known to directly lead to worsening of insulin sensitivity (the key and defining aspect of type 2 diabetes)," said Dr. Weickert, who was not involved in the new research.

SOURCE: http://bit.ly/2FEsPM5

Science 2018.