Humans carry around trillions of microbes in their gastrointestinal tracts, and research has shown that the gut microbiome is closely linked to health. Studies have found that gut microbiomes are more healthy when they are made up of more diverse microbes, for example, and imbalances in the microbiome, or dysbiosis, is associated with disease. Scientists are now starting to look more closely at the specific types of microbes in the gut, and exactly how certain strains are influencing the development of specific disorders. A new report in Diabetes has identified two strains of gut microbes that seem to affect insulin sensitivity.
A multitude of studies have associated the microbiome with metabolic disease. For example, research has indicated that people who have lower levels of bacteria that generate butyrate, a fatty acid, also don't process insulin correctly.
In this new study, a bacterium called Coprococcus was found at higher levels in people who tended to have more sensitivity to insulin, while higher levels of a bacterium called Flavonifractor were found in those who tended to be less insulin sensitive. Coprococcus may be protecting people from type 2 diabetes while Flavonifractor could be promoting the development of type 2 diabetes.
But it's also important to decipher whether microbes can cause disease, or if differences in the microbiome arise after the disease is present. Senior study author Mark Goodarzi, MD, Ph.D., the director of the Endocrine Genetics Laboratory at Cedars-Sinai, is also the principal investigator of a multicenter study called Microbiome and Insulin Longitudinal Evaluation Study (MILES), which is aiming to determine whether factors in the microbiome cause diabetes, or if diabetes changes the microbiome.
Since 2018, MILES researchers have been assessing data from Black and non-Hispanic white adults who are 40 to 80 years old. In this study, the focus was on 352 study volunteers who had not been diagnosed with diabetes. These volunteers gave stool samples, did glucose tolerance tests, and supplied other information such as data about dietary habits. In this group, 135 were found to have prediabetes and 28 people had glucose tolerance tests that met the threshold for a diabetes diagnosis.
The researchers examined 36 gut bacteria that generate butyrate in the study participants (from the stool samples), and found that Coprococcus and related bacteria are good for insulin sensitivity.
Although Flavonifractor also generates butyrate, it was associated with insulin resistance. This confirms previous research that has found higher Flavonifractor levels in diabetic people. These findings were significant after the researchers controlled for other factors that affect the development of diabetes, including sex, race, body mass index, and age.
The study authors cautioned, however that people should not yet try to change their microbiome to lower their risk of diabetes.
"As far as the idea of taking probiotics, that would really be somewhat experimental," said Goodarzi. More research is needed to determine exactly which bacteria should be altered "... but it's coming, probably in the next five to ten years."
Now the researchers want to learn more about how diet changes the microbiome, and they are planning to follow up with study volunteers to learn more about changes in insulin resistance and the microbiome over time.
Sources: Cedars-Sinai Medical Center, Diabetes
