Common sweeteners may be doing much more inside our bodies than simply replacing sugar. Scientists at the University of Cambridge have discovered that many widely used sweeteners can directly interfere with the growth of gut bacteria, and their effects can become even more pronounced when combined with medications or other everyday substances.

In laboratory experiments involving 39 sweeteners and 25 species of gut bacteria, researchers found that roughly three-quarters of the sweeteners altered the growth of at least one bacterial species. Some slowed or completely stopped the growth of microbes associated with a healthy digestive system.

One combination stood out in particular. When the sweetener isosteviol was paired with the antidepressant duloxetine, it strongly suppressed two important gut bacteria involved in maintaining digestive health and regulating blood sugar.…