Kiran Patil and colleagues at the University of Cambridge found that sweeteners can slow the growth of certain gut bacteria in laboratory tests. Their study, published in Molecular Systems Biology, also found that isosteviol combined with duloxetine strongly suppressed two species, Roseburia intestinalis and Parabacteroides merdae.
University of Cambridge study
The researchers grew 25 gut bacterial species and exposed each culture to 39 common, commercially used sweeteners. Around three-quarters of the sweeteners changed how at least one species grew, and some slowed or stopped bacteria linked to a healthy gut.
Patil said, "Most of what we know about the potential impact of sweeteners on our health comes from animal research or from population studies." He also said, "it's difficult to know how sweeteners act in the body – is it through direct interactions with our gut bacteria?"
Sonja Blasche on combinations
The team then tested the sweeteners with caffeine, vanillin, advantame and eight commonly used drugs. It found over 100 interactions in which the sweeteners behaved differently when paired with another substance, with 34 cases making the effects stronger and 68 making them weaker.
Sonja Blasche, the lead author at the MRC Toxicology Unit, said, "Answering this is further complicated by the fact that we rarely ever take sweeteners by themselves – we take them with drinks, in snacks, or even in medication to mask bitterness,"
Isosteviol and duloxetine
The strongest paired effect involved isosteviol and duloxetine, which strongly suppressed Roseburia intestinalis and Parabacteroides merdae. The combination stands out because duloxetine was prescribed to over 4.2 million patients in the US in 2023, putting the lab result next to a drug many people already take.
Patil's group said more research is needed to understand the real-world health impacts of the laboratory findings. For now, the clearest next step is to treat sweeteners as ingredients that may not act alone when they are consumed with drinks, snacks or medication.
