Research Suggests Gut Bacteria Could Play a Role in Diabetes


It is too early to know how patients could potentially change their microbiome to reduce their diabetes risk.

New research has found that individuals with higher levels of Coprococcus bacteria in the gut tended to have higher insulin sensitivity, whereas those whose microbiomes had higher levels of the bacterium Flavonifractor tended to have lower insulin sensitivity.

Investigators have long tried to understand why individuals develop diabetes by studying the composition of the microbiome, which is believed to be affected by medications and diet. Researchers have found that patients who do not process insulin properly have lower levels of a certain type of bacteria that produce a type of fatty acid called butyrate.

An ongoing investigation, called Microbiome and Insulin Longitudinal Evaluation Study (MILES), is following and observing individuals at risk for diabetes to learn whether those with lower levels of these bacteria develop the disease.

“The big question we’re hoping to address is: Did the microbiome differences cause the diabetes, or did the diabetes cause the microbiome differences?” said senior author Mark Goodarzi, MD, PhD, director of the Endocrine Genetics Laboratory at Cedars-Sinai, in a press release.

Investigators involved in MILES have been collecting information from participating Black and non-Hispanic white adults between 40 and 80 years of age since 2018. An earlier cohort study from the trial found that birth by cesarean section is associated with a higher risk for prediabetes and diabetes.

In the most recent study out of the MILES trial, investigators analyzed data from 352 individuals without known diabetes who were recruited from the Wake Forest Baptist Health System in Winston-Salem, North Carolina. Study participants were asked to attend 3 clinic visits and collect stool samples prior to the visits, and investigators analyzed data collected at the first visit.

For example, they conducted genetic sequencing on the stool samples to study the participants’ microbiomes, and to specifically look for bacteria that earlier studies have found to be associated with insulin resistance. Each participant also filled out a diet questionnaire and took an oral glucose tolerance test, which was used to determine the ability to process glucose.

The investigators found that 28 participants had oral glucose tolerance results that met the criteria for diabetes. They also found that 135 individuals had prediabetes, a condition in which a person’s blood sugar levels are higher than normal but not high enough to meet the definition of diabetes.

The team also analyzed associations between 36 butyrate-producing bacteria found in the stool samples and a person’s ability to maintain normal levels of insulin. They controlled for factors that could also contribute to a person’s diabetes risk, such as age, sex, body mass index, and race.

Coprococcus and related bacteria formed a network of bacteria with beneficial effects on insulin sensitivity, according to the study. Despite being a producer of butyrate, Flavonifractor was associated with insulin resistance. Earlier research has found higher levels of Flavonifractor in the stool of individuals with diabetes.

Investigators are continuing to study samples from patients who participated in this study to learn how insulin production and the composition of the microbiome change over time. They also plan to study how diet may affect the bacterial balance of the microbiome.

Goodarzi noted, however, that it is too early to know how patients could potentially change their microbiome to reduce their diabetes risk.

“As far as the idea of taking probiotics, that would really be somewhat experimental,” Goodarzi said in the press release. “We need more research to identify the specific bacteria that we need to be modulating to prevent or treat diabetes, but it’s coming, probably in the next 5 to 10 years.”


Gut Bacteria May Play a Role in Diabetes. News release. Cedars Sinai; January 3, 2023. Accessed January 11, 2023.

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