New findings link gut bacteria with diabetes risk, but questions remain
An ongoing study led by researchers at Cedars-Sinai is investigating the relationship between our gut microbiome and the development of type 2 diabetes. Early data from the study indicates bacteria producing a specific fatty acid can be linked to healthier blood sugar levels.
Dubbed MILES (the Microbiome and Insulin Longitudinal Evaluation Study), the long-term study has recruited around 350 non-diabetic participants. The plan is to follow the cohort for over two years, assessing each subject's microbiome and glucose tolerance three times over the study period.
According to Mark Goodarzi, lead researcher on the study, the goal is to discern changes over time between insulin homeostasis and gut bacteria. Basically, the researchers are trying to ascertain what comes first – the development of diabetes or changes to the gut microbiome.
“The big question we're hoping to address is: Did the microbiome differences cause the diabetes, or did the diabetes cause the microbiome differences?” explained Goodarzi.
Although the study is ongoing, Goodarzi and colleagues have published some early findings, reporting on the baseline data gathered from each participant's first assessment. These initial findings, recently published in the journal Diabetes, reveal a distinct correlation between insulin sensitivity and certain species of gut bacteria known to produce a short chain fatty acid called butyrate.
Prior studies have suggested one key factor in healthy microbiomes is the presence of high levels of butyrate-producing gut bacteria. Butyrate has recently been implicated in healthy aging, and is suspected to protect from auto-immune disease. A 2020 study found subjects with prediabetes displayed notably lower-levels of butyrate-producing gut bacteria compared to healthy people.
These new findings added to this growing body of knowledge by focusing on 36 different strains of butyrate-producing bacteria, revealing a network of five species in particular seemed to be associated with the greatest benefits on insulin sensitivity: Coprococcus comes, Oscillibacter sp. CAG 241, Alistipes finegoldii, and Faecalibacterium prausnitzii.
"The members of this group were highly intercorrelated in abundance level, suggestive of a functional network," the researchers write in the new study. "Three members of this group were associated with higher circulating butyrate levels, providing support for the hypothesis that this group of bacteria may improve metabolism by producing butyrate, which is then absorbed systemically where it can improve insulin homeostasis."
Complicating the findings, the researchers detected two butyrate-producing species – Flavonifractor plautii and Anaerostipes caccae – were negatively associated with insulin sensitivity. This isn't the first study to associate these particular bacterial species with an increased risk of diabetes but they do raise questions about the straightforward link between butyrate-producing bacteria and metabolic health.
"A possible explanation for enrichment of specific butyrate producers in individuals with dysglycemia is that these taxa may carry genes that code for other processes that counteract the beneficial effects of butyrate or otherwise adversely affect metabolism," the researchers speculate in the study. "Another possible explanation is that such butyrate producers cooccur with butyrate-consuming species or other taxa that produce harmful metabolites."
According to Goodarzi, these discordant findings mean it's too soon to suggest some kind of butyrate-producing probiotic cocktail could prevent diabetes. In fact, considering some butyrate-producing species could potentially contribute to the development of diabetes, it may be risky to try and play with our microbial makeup before more research can provide a better understanding of what is going on.
MILES is ongoing, and the researchers hope its longitudinal nature will offer some insights into the causal relationship between insulin sensitivity and gut bacterial changes. Goodarzi is optimistic scientists will eventually solve this mystery, and maybe in the near future diabetes could be treated with probiotic cocktails.
“As far as the idea of taking probiotics [right now], that would really be somewhat experimental,” said Goodarzi. “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.”
The new study was published in the journal Diabetes.