Alternative sweeteners, frequently found in low-calorie and sugar-free products, may disrupt the growth of bacteria essential for gut health, according to a new study. Researchers discovered that these sweeteners can alter the composition of the gut microbiome, a complex ecosystem of microorganisms that plays a crucial role in digestion, immunity, metabolism, and even mental well-being.
When the balance of the gut microbiome is disturbed, it has been linked to an increased risk of chronic conditions such as obesity, heart disease, diabetes, depression, and certain cancers. The study, conducted at the University of Cambridge, exposed 25 different bacterial species, including those considered beneficial, neutral, or potentially harmful, to 39 common sweeteners. Approximately three-quarters of the sweeteners tested affected the growth rate of at least one bacterial species, with several inhibiting the proliferation of bacteria associated with a healthy digestive system.
"Sweeteners are often marketed as metabolically neutral, but our study challenges this idea," said Dr. Sonja Blasche, a lead author of the study. "These common combinations could have unintended effects on our gut microbiome."
The research extended to examine how sweeteners interact with other substances. Scientists paired sweeteners with compounds like caffeine, vanilla extract, and eight frequently used medications. This revealed over 100 instances where a sweetener’s impact on gut bacteria changed in the presence of another compound. In 34 cases, the combined effect was intensified, while in 68 cases, it was weakened.
A significant finding involved isosteviol, a compound derived from stevia leaves, and duloxetine, an antidepressant marketed under brand names like Cymbalta. When combined in laboratory settings, this pairing strongly suppressed the growth of Roseburia intestinalis and Parabacteroides merdae, two bacterial species important for gut health and metabolic regulation.
Duloxetine is widely prescribed for depression, anxiety, and chronic pain, with over 4.2 million U.S. patients receiving prescriptions in 2023. In a simulated gut microbiome environment, the combination of isosteviol and duloxetine reduced microbial diversity, a marker often associated with a resilient gut, and altered the microbial community structure. Further experiments suggested these changes could increase toxicity to host cells and disrupt inflammatory and immune responses.
"Our study suggests that artificial sweeteners don’t just pass through the body passively — they can interact with gut microbes, and these effects can be amplified or altered by other substances like medications," stated Professor Kiran Patil, the study’s senior author.
While the study highlights potential interactions, it does not definitively prove that sweeteners or their combinations directly cause harm in humans. However, it contributes to ongoing research into the potential health influences of sweeteners, including investigations into their possible links with type 2 diabetes, obesity, and cancer. The researchers plan to investigate whether these interactions occur in people, the necessary dosages, and their actual impact on health.
Sweeteners continue to be widely consumed, with about 40% of Americans regularly using sugar substitutes as they seek to reduce calorie intake and as food manufacturers reformulate products.