A screen of 39 sweeteners
Scientists at the University of Cambridge ran 39 sweeteners against 25 species of gut bacteria in laboratory experiments. About three-quarters of the sweeteners changed the growth of at least one species. Some slowed or completely stopped the growth of microbes associated with a healthy digestive system.
The work, published in Molecular Systems Biology, is one of the few systematic attempts to test sugar substitutes directly against individual gut bacteria rather than relying on animal studies or comparisons of diet and health across large groups of people.
The combination that stood out
One result drew more attention than the rest. When the sweetener isosteviol was paired with duloxetine, a widely prescribed antidepressant, the combination strongly suppressed two gut bacteria involved in maintaining digestive health and regulating blood sugar. It also disrupted the balance of a simulated gut microbiome and produced changes that could bear on inflammation and immune response.
The finding matters because people rarely consume one substance at a time. Sweeteners appear in soft drinks, desserts, packaged snacks and breakfast cereals, and many of the people using them also take prescription medicines. Testing single compounds against single bacterial strains can miss interactions that occur in a real gut.
What the study does not show
The researchers stress that the experiments were done in the lab, not in humans. Whether the effects seen in a dish translate into changes in a person's microbiome, and whether those changes would matter for health, is not known.
Earlier research has found associations between sweetener consumption and conditions including type 2 diabetes, obesity and cancer. Associations do not prove cause, and scientists are still working out the mechanisms that might explain them. The gut microbiome is one candidate: it helps break down food, produces useful compounds, supports the immune system and contributes to metabolic health.
The Cambridge group says the next step is to test the most active combinations in more realistic models and, eventually, in people. Until then, the practical reading is not that sweeteners are dangerous, but that the assumption they pass through the body without touching gut microbes is too simple.