Researchers at the University of Cambridge tested 39 sweeteners on gut bacteria. Three out of four affected bacterial growth, and in combination with medicines some effects were markedly amplified.
Sweeteners are often regarded as a harmless alternative to sugar because they provide hardly any calories. A laboratory study by the MRC Toxicology Unit at the University of Cambridge calls into question the idea that they leave no trace in the gut. The work was published in the journal Molecular Systems Biology.
39 sweeteners, 25 bacterial species
The team led by Sonja Blasche and Kiran Patil tested 39 natural and artificial sweeteners on 25 typical gut bacteria, including beneficial, neutral and potentially harmful species. About three quarters of the sweeteners altered the growth of at least one species. Several inhibited or stopped bacteria associated with healthy digestion.
Interactions with medicines
Combinations were particularly striking. The researchers mixed sweeteners with caffeine, vanillin and eight commonly used medicines. In more than 100 cases, this changed the effect on the bacteria, sometimes amplifying it, sometimes weakening it. The strongest effect was seen with the stevia derivative isosteviol together with the antidepressant duloxetine: the combination markedly suppressed two beneficial bacterial species and reduced diversity in an artificially assembled gut community.
Editorial assessment
These are purely laboratory experiments. In the body, sweeteners are partly absorbed, diluted or broken down before they reach the gut bacteria. Whether the observed effects occur in humans and are relevant to health remains open. Studies in humans with realistic amounts are needed for this. People taking medicines should therefore not change anything on their own initiative. However, the study is a further indication that sweeteners are not as neutral as is often assumed.
Sources
- Blasche S. et al., Molecular Systems Biology 2026, DOI: 10.1038/s44320-026-00225-6
- ScienceDaily, 17.07.2026
