Scientists have discovered a link between the gut microbiome and the risk of diabetes

The composition of intestinal bacteria may indicate the risk of developing type 2 diabetes even before blood tests show abnormalities. This conclusion was reached by scientists who studied the data of more than 229 thousand people. What exactly the researchers found and whether microbiome analysis can be used for early risk assessment is described in the "Izvestia" article.

What the scientists were looking for

Type 2 diabetes and prediabetes are detected using blood tests: the level of glycated hemoglobin HbA1c, fasting glucose, or how the body copes with glucose intake are determined. Prediabetes is a condition in which sugar is already higher than normal, but has not yet reached the values that make it possible to diagnose diabetes. When assessing the risk of the disease, doctors also take into account age, body weight and family history.

The authors of the new study raised another question: is it possible to see signs of distress earlier, as long as the standard glucose levels remain within the normal range. Their attention was drawn to the gut microbiome, a community of microorganisms whose composition is related to nutrition, lifestyle, and body condition.

Previous studies have already found differences between the microbiome of people with and without diabetes. However, when comparing large groups, scientists did not always get the same set of bacteria associated with the disease. The team of Gabriel Baldanzi and Nicola Segata from the University of Trento, together with colleagues from the UK, decided to test these connections on a larger sample.

The researchers compared information about the participants' health with metagenomic data — DNA sequences of microorganisms found in the intestine. A total of 229,025 people were included in the analysis; the average age was 50 years, 73.8% of the participants were women. 3,627 people had type 2 diabetes and 14,022 had prediabetes. The remaining 211,376 had glucose levels within the normal range.

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Which bacteria have been linked to diabetes?

After taking into account age, gender and body mass index, the scientists found 789 bacterial species, the number of which differed in people with and without type 2 diabetes. Of these, 168 species were found in the participants with the disease in greater numbers, and 621 species — in a smaller number. We are talking about statistical relationships: by itself, the discovery of a specific bacterium does not mean that a person has diabetes or will necessarily develop it in the future.

The authors cite Enterocloster bolteae as an example: people with diabetes had more of this bacterium. Another species, Romboutsia timonensis, on the contrary, was less common among them. Some of the microorganisms included in the detected profile have so far been poorly studied: some species have been identified from genetic data, although they have not yet been isolated or grown in the laboratory.

The differences were especially noticeable in participants who took diabetes medications. This is essential for interpreting the results: treatment itself can affect the composition of the microbiome. However, scientists also observed characteristic changes in people with diabetes who did not take medications. In addition, 587 out of 789 types were associated with prediabetes in participants who did not receive drug treatment.

He also mentioned the possibility of an earlier choice of treatment. So far, this is a promising approach, not a proven method of prevention based on microbiome analysis.

What was found in people with normal glucose levels

The next step was to examine data from 135,093 participants who had neither diabetes nor prediabetes. They compared the composition of their microbiome with glucose levels for two hours after eating.

After eating, sugar levels usually rise and then decrease. If it remains elevated for longer, it may indicate that the tissues are responding less well to insulin. This reaction is considered as one of the early signs of metabolic disorders associated with the development of type 2 diabetes.

People who had high sugar after eating for longer had a higher microbial profile, which was typical for participants with diabetes. According to the authors, the differences in bacterial composition became more noticeable as the signs of insulin resistance increased. It is this part of the study that suggests a potential additional marker of risk in people whose normal glucose levels are still normal.

However, there is a fundamental limitation here. The work shows the relationship between the composition of the microbiome and already measured health indicators and the body's response to food. The data presented do not establish how many participants subsequently developed diabetes and how accurately microbiome analysis is able to predict such an outcome in a particular person. It is also impossible to conclude from them that the detected bacteria themselves cause the disease.

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Is it now possible to take a microbiome test instead of a blood test

The authors of the study explicitly state that the study of the microbiome should not replace standard examinations for the diagnosis of diabetes and prediabetes. In the future, information about intestinal bacteria may complement risk assessment based on age, body mass index, and family history. However, for practical application, it will be necessary to check whether such an analysis provides reliable additional information and helps to choose effective preventive measures. Scientists also suggest that observing changes in the microbiome could show people the result of lifestyle changes.

According to him, the discovery of early changes in the microbiome could be an additional motivation to continue these changes. This possibility also needs to be checked.

The significance of the work, according to Nicola Segata, head of the Computational Metagenomics laboratory at the University of Trento, is related to both the sample size and the methods of processing genetic data. For the first time, the researchers identified some of the bacteria included in the identified profile directly from these data. This expands the understanding of the diversity of intestinal microorganisms, but at the same time shows how much remains to be learned about their properties and possible role in the development of the disease.

So far, the practical conclusion remains the same: people with risk factors should discuss the examination with a doctor, and assess their sugar levels using verified blood tests. Dietary changes and regular physical activity are already being used to reduce the risk of type 2 diabetes. Over time, the new result may help to determine more precisely who needs prevention, but it does not yet provide a ready-made diagnostic test.