One type of bacteria found in the gut may contribute to the development of type 2 diabetes, while another may protect from the disease, according to early results from an ongoing, prospective study recently published in Diabetes.
Researchers led by Mark Goodarzi, MD, PhD, director of the Endocrine Genetics Laboratory at Cedars-Sinai Medical Center in Los Angeles point out that for years, investigators have sought to understand why people develop diabetes by studying the composition of the microbiome. “Studies have implicated genetic factors, unhealthy diet, insufficient physical activity, suboptimal sleep, and obesogenic environmental factors. A recent addition is dysbiosis of the gut microbiome,” the authors write. “The Microbiome and Insulin Longitudinal Evaluation Study (MILES) seeks to define the effect of the gut microbiome on the three insulin homeostasis traits whose dysfunction leads to type 2 diabetes.”
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 MILES trial found that birth by cesarean section is associated with a higher risk for developing prediabetes and diabetes.
For the most recent study to come out of this ongoing trial, investigators analyzed data from 352 people without known diabetes who were recruited from the Wake Forest Baptist Health System in Winston-Salem, North Carolina. Study participants were asked to attend three clinic visits and collect stool samples prior to the visits. Investigators analyzed data collected at the first visit. They conducted genetic sequencing on the stool samples to study the participants’ microbiomes, and 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 ability to process glucose.
Investigators found 28 people had oral glucose tolerance results that met the criteria for diabetes. They also found that 135 people 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 research team 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. Despite being a producer of butyrate, Flavonifractor was associated with insulin resistance; prior work by others have found higher levels of Flavonifractor in the stool of people 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 emphasizes, however, that it is too early to know how people can change their microbiome to reduce their diabetes risk. “As far as the idea of taking probiotics, that would really be somewhat experimental,” says Goodarzi, who is also the Eris M. Field Chair in Diabetes Research at Cedars-Sinai. “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 five to 10 years.”