Metformin may alter the gut microbiome

Metformin, a commonly prescribed drug used for type 2 diabetes treatment, may have greater impacts on the gut microbes than the actual disease. Researchers believe a new study might have major consequences for current and future studies seeking correlations between disease and our microbiomes. The study, published in Nature, may allow new methods for scientists to gain a comprehensive understanding of metformin, specifically how it works, while also minimizing the drug's side effects.

The researchers, surprised that this drug activates obvious changes in gut microbes, believe their research may replicate itself in future studies regarding alterations to the gut and disease treatment. Consider the number of drugs in existence and the amount of people that take several daily medications. Any number of drugs could be significantly shaping the gut microbiome, ultimately resulting in dysbiosis.

They believe that even if only a small fraction of medications have these severe effects, they may still be dramatically influencing the gut.

Metformin, typically taken over the course of years in high doses, is prescribed as a type 2 diabetes treatment to manage blood sugar. Researchers aren’t exactly sure of the mechanisms reacting from the drug inside patients’ bodies.

Studying Metformin and the Gut Microbiome

European Molecular Biology Laboratory (EMBL) scientists in Heidelberg, Germany, and their colleagues in the MetaHIT consortium compared stool samples taken from nearly 800 people, including healthy individuals and type 2 diabetes patients. Simply observing the microbes found in a person’s stool did not reliably diagnose diabetes, unless the diabetic patient was using metformin. Patients taking metformin had significantly higher levels of Escherichia coli and lower levels of Intestinibacter bartlettii than the microbiomes of healthy people as well as type 2 diabetes patients not taking metformin.

The study did not reveal that other types of antidiabetic drugs affected the gut microbiota. However, when studying type 2 diabetes patients not treated by metformin, they did discover that patients, from Denmark, China or Sweden, had fewer bacteria that produce the colon health-promoting short-chain fatty acids.

The variances observed in the gut bacteria communities might enlighten users to some of metformin’s side effects, insinuating that metformin users might potentially rebalance the gut microbiome. The researchers hypothesize that specific bacteria may someday help control the gut microbiome balance in those taking metformin and potentially other drugs that may cause dysbiosis and inflammation.

These findings may also clarify previously contradictory studies that failed to establish exactly how the bacterial communities in the gastrointestinal (GI) tract fluctuate between healthy individuals and type 2 diabetes patients. Researchers believe these contradictions stemmed from the disparities in metformin users between the studies.

Scientists seeking specific microbes to be used as a diagnostic test or treatment for diseases like diabetes, this study emphasizes the significance of treatments and their influence on the results.


Forslund, K., Hildebrand, F., Nielsen et al. Disentangling type 2 diabetes and metformin treatment signatures in the human gut microbiota, Nature. 2015. doi:10.1038/nature15766

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