Scientists from the University of Cambridge have found that many widely used sweeteners can directly affect the growth of gut bacteria, with some combinations involving medications producing unexpectedly strong effects.
The findings, published in Molecular Systems Biology, are based on laboratory experiments and do not demonstrate that sweeteners cause health problems in humans. However, the researchers say the results highlight the need to better understand how these ingredients interact with the gut microbiome.
The team tested 39 natural and artificial sweeteners on 25 species of gut bacteria, including beneficial, neutral, and potentially harmful microbes. Around 75% of the sweeteners influenced the growth of at least one bacterial species, and several inhibited bacteria associated with digestive health.
Researchers also investigated how sweeteners behave when combined with other commonly consumed substances, such as caffeine, vanilla flavoring, artificial sweeteners, and prescription drugs. More than 100 interactions were identified, with some combinations strengthening and others weakening the sweeteners' effects on gut bacteria.
The most striking results involved isosteviol, a sweetener used in the food industry, and the antidepressant duloxetine. Together, they significantly reduced the growth of Roseburia intestinalis and Parabacteroides merdae, two bacterial species linked to digestive health, blood sugar regulation, and immune function.
In a simplified laboratory model of the gut microbiome, the combination also reduced microbial diversity—generally considered an indicator of a healthy and resilient gut ecosystem—and altered the balance between bacterial species. Additional experiments suggested that these changes increased toxicity toward certain cells and affected immune and inflammatory responses.
The researchers emphasize that the study was conducted entirely under laboratory conditions. Human digestive systems are far more complex, and factors such as diet, genetics, metabolism, medication use, and existing gut microbiota may influence how sweeteners behave in the body.
"Our study suggests that artificial sweeteners are not biologically inactive," said Professor Kiran Patil, senior author of the study. "They can interact with gut microbes, and these effects may be modified or amplified by other substances, including medications."
The scientists say further clinical studies are needed to determine whether these microbial changes occur in people and whether they have meaningful consequences for human health.
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