Health

These common sweeteners could be silently damaging gut, study finds

Newsweek · Jul 16, 2026 17:03 · 4 min read

Woman hand throwing saccharin pills on coffee cup in the kitchen at home. — A stock image of a close up hand adding saccharin pills into coffee cup.

One widely used sweetener had a surprising impact when paired with a common medication.

Artificial sweeteners are commonly promoted as healthier alternatives to sugar and are found in everything from soft drinks and desserts to cereals and snacks. But new research suggests they may have a direct effect on the bacteria that live in our gut.

Scientists from the University of Cambridge in England examined 39 commercially used sweeteners—both artificial and natural—and measured their effects on the growth of gut bacteria.

One compound in particular, isosteviol, derived from stevia, had a striking effect when combined with duloxetine, an antidepressant prescribed to more than 4.2 million patients in the United States in 2023, according to drug database ClinCalc. The findings were published in Molecular Systems Biology.

“We expected some interaction, but not as strong as the experiments revealed,” Professor Kiran Patil, of the Medical Research Council (MRC) Toxicology Unit at the University of Cambridge, told Newsweek.

These common sweeteners could be silently damaging gut, study finds — Stock image: a close-up hand adds saccharin pills into a coffee cup.

“Sweeteners are often marketed as metabolically neutral, but our study challenges this idea,” Dr. Sonja Blasche, lead author of the study from the MRC Toxicology Unit, said in a statement.

How Researchers Studied Sweeteners and Gut Bacteria

The study examined how artificial and low-calorie sweeteners affect the bacteria living in the gut and whether those effects change when sweeteners are consumed alongside other substances such as caffeine, flavorings or medications.

To investigate, researchers grew 25 species of gut bacteria in the lab, including beneficial, neutral and potentially harmful strains. They then exposed each bacterial culture to almost 40 commonly used sweeteners and measured how well the microbes multiplied.

The most notable interaction involved isosteviol and the antidepressant duloxetine.

The combination strongly suppressed Roseburia intestinalis and Parabacteroides merdae, two gut bacteria that play important roles in maintaining a healthy digestive system.

Patil told Newsweek: “We were surprised that isosteviol specifically interacted with duloxetine. Our data suggests that other medications, especially those that are bioaccumulated or metabolized by gut bacteria, may also interact with sweeteners.”

Reduced Microbial Diversity

Because gut bacteria function as part of a wider community rather than in isolation, the researchers also created a synthetic microbial community containing all 25 bacterial species.

When they tested the sweetener-drug combinations in this model, they found that the combination of isosteviol and duloxetine reduced microbial diversity. A diverse microbiome is generally considered important for good gut health.

“Previous studies have shown links between sweeteners, microbiome, and glucose homeostasis. Our study is in vitro and thus does not offer any direct dietary or nutritional advice. Our results warrant viewing sweeteners as biologically active compounds rather than inert additives,” Patil told Newsweek.

More Than 100 Interactions Identified

Around three-quarters of the sweeteners altered the growth of at least one bacterial species. Some slowed down or stopped the growth of bacteria associated with a healthy gut.

Blasche said in a statement: “We found that they can directly affect gut bacteria, particularly when mixed with other compounds such as medication and food additives. These common combinations could have unintended effects on our gut microbiome.”

The team then tested each sweetener alongside common compounds including caffeine, vanillin, advantame and eight commonly used medications.

They identified more than 100 interactions in which sweeteners behaved differently when combined with another substance. In 34 cases, the combinations strengthened the effects, while in 68 cases the effects became weaker.

Further analysis showed that some combinations increased toxicity toward certain host cells and interfered with cells involved in inflammation and immune responses.

What the Findings Mean

Despite the findings, the researchers emphasized that their experiments were conducted in the laboratory rather than in people.

As a result, more research is needed before it can be determined whether these effects translate into direct health consequences in humans. However, the study offers an early insight into how sweeteners may interact with gut bacteria, particularly when consumed alongside other commonly used substances such as medications.

Dr. Memee Ahmad told Newsweek: “It’s worth being clear that this was laboratory work using isolated bacteria and a simplified synthetic community, not a human trial, so it does not prove harm in people taking these together. But it adds to a wider pattern.”

Ahmad noted that the World Health Organization’s 2023 guidance stopped short of recommending sweeteners for weight control, while a systematic review published earlier this year concluded that the routine use of sweeteners in diabetic diets cannot currently be recommended based on the available evidence.

“My take is that sweeteners are still a reasonable short-term tool, but the blanket ‘safe sugar alternative’ message is increasingly outdated, particularly for patients on multiple medications where these interactions have barely been studied,” Ahmad said.