Low-calorie sweeteners are in diet soda, protein bars, yogurt and a lot of “sugar-free” snacks. A new lab study from the University of Cambridge asks a narrow question: what do they do to the bacteria that live in our gut? The answer is interesting, but it is far from a verdict on your diet soda.
What the researchers did
The team grew 25 species of gut bacteria in dishes, including ones thought to be helpful, neutral or potentially harmful. They then exposed the cultures to 39 commercially available sweeteners, both artificial and plant-derived. They also tested sweeteners alongside caffeine, vanillin and eight widely used drugs, then built a simplified “mini gut” community of all 25 species to see how combinations changed the mix.
What they found
- About three in four sweeteners changed the growth of at least one bacterial species. Some slowed growth; a few stopped it.
- Effects differed a lot by sweetener and by species, so “sweeteners” is not one single thing.
- In more than 100 cases, a substance behaved differently when paired with another ingredient. The effect grew stronger in 34 cases and weaker in 68.
- One pairing stood out: the sweetener isosteviol with the antidepressant duloxetine strongly suppressed two species linked to gut health and blood sugar control, and reduced diversity in the mini community.
The researchers note that more than 4.2 million U.S. patients received duloxetine prescriptions in 2023, which is why interactions with common ingredients are worth studying.
The catch
This was a laboratory study on isolated bacteria and a simplified community, not on people or animals. The human gut is vastly more complex, and doses in a dish are not the same as what reaches your intestines after a drink. The study does not show that anyone taking duloxetine is harmed by eating isosteviol, and the authors describe the work as a foundation for later research, not evidence that sweeteners are harmful.
What it means for you
Mostly, it is a reminder that food ingredients, drugs and gut bacteria can influence one another in ways that nobody has fully mapped. If you take a prescription medication and have questions about what you eat or drink, a pharmacist is a good, free place to ask. For everyone else, this study is a signal for scientists to dig further, not a reason to change your habits today.
This article is for general information, not medical advice.
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