Saccharin may lead to high blood sugar levels by changing gut bacteria in some people, but other artificial sweeteners may not have the same effect.
Israeli researchers allowed mice access to one of six liquids: water sweetened with saccharin, sucralose, aspartame, glucose, sucrose, or nothing. After 11 weeks, the authors reported that, as a group, the mice drinking the three artificial sweeteners had worse glucose tolerance—that is, their blood sugar rose higher after they were given a very sugary drink—than the other mice. (However, the mice fed aspartame appeared to have little or no glucose intolerance, and saccharin and sucralose affected only some “responders.”)
Glucose tolerance was normal in all mice after the researchers gave them antibiotics, suggesting that saccharin and sucralose had altered the gut bacteria of some mice.
For all other experiments, the researchers used only saccharin. When they transferred gut bacteria that had been mixed with saccharin (in a test tube) to germ-free mice, the animals’ glucose tolerance got worse. When they gave seven people a high dose of saccharin for a week, four “responders” had worse glucose tolerance at the end than at the beginning of the week. And when they transferred stool from the human responders to germ-free mice, the animals’ glucose tolerance got worse.
What to do: It’s too early to draw any conclusions from this study, but you’re better off drinking water. And don’t switch from diet drinks to sugary beverages. The best human studies find that sugary drinks cause weight gain and are linked to a higher risk of diabetes, while diet sodas (typically sweetened with aspartame) are not. (Some studies find a link between diet soda and obesity or diabetes only because those conditions lead people to switch to diet soda, not because diet soda causes those conditions.)
Source: Nature 2014. doi:10.1038/nature137934