Scientists tested 39 sweeteners and uncovered surprising gut effects
Scientists have discovered that many common sweeteners can interfere with gut bacteria, with some combinations involving medications producing surprisingly strong effects. One sweetener mixed with a widely prescribed antidepressant reduced beneficial bacteria and microbial diversity in laboratory experiments, raising new questions about potential effects on gut health and immunity.
Key points
- Cambridge scientists found about three-quarters of 39 tested sweeteners changed growth of at least one gut bacterial species.
- Combining isosteviol with the antidepressant duloxetine strongly suppressed two gut bacteria and cut microbial diversity.
- Researchers stress the work was done in the laboratory, not in humans, and more studies are needed.
Laboratory experiments at the University of Cambridge have found that many common sweeteners can directly affect the growth of gut bacteria. In tests involving 39 sweeteners and 25 species of gut bacteria, roughly three-quarters of the sweeteners changed the growth of at least one bacterial species, with some slowing or halting microbes linked to a healthy digestive system. The findings were published in Molecular Systems Biology.
The team also tested sweeteners alongside other substances, including caffeine, vanillin, advantame and eight widely used drugs. These combinations produced more than 100 cases in which a sweetener's effect on bacterial growth changed, with 34 becoming stronger and 68 becoming weaker.
Sweetener and antidepressant combination
One pairing stood out: isosteviol, a sweetener used in the food and beverage industry, strongly inhibited the gut bacteria Roseburia intestinalis and Parabacteroides merdae when combined with the antidepressant duloxetine. In a simplified artificial gut community containing all 25 species, the same combination reduced bacterial diversity and shifted the abundance of different species.
The researchers report that more than 4.2 million patients in the United States received prescriptions for duloxetine in 2023. They say the results do not show that people taking the drug experience these effects or that combining it with isosteviol is harmful.
Sweeteners are often marketed as metabolically neutral, but our study challenges this idea.
— Dr. Sonja Blasche
Cautions and funding
The scientists note that all experiments were conducted in the laboratory using isolated cultures or simplified communities, not in humans, and that further studies are needed to learn whether the effects occur in real-world conditions. The research was funded by the European Union's Horizon 2020 program and the UK Medical Research Council.
