A study published in the journal Molecules found that six of the most common artificial sweeteners are actually toxic for bacteria living in the digestive gut. The digestive gut plays an important role in human metabolism for breaking down foods and substances that we drink. So ingesting anything that could mess that up would not be very good.
The researchers tested six artificial sweeteners, aspartame, sucralose, saccharine, neotame, advantame, and acesulfame potassium-k, on lab mice. They found that just one milligram per milliliter of artificial sweetener was enough to turn the bacteria in their digestive gut toxic. So while it may take slightly more sweetener to turn a human's digestive bacteria toxic, you also have to remember that humans are also consuming these sweeteners are much higher levels.
These results suggest that ingesting high amounts of artificial sweeteners can create a number of health problems in humans, most prominently glucose intolerance.
This actually isn't the first time artificial sweeteners have been called out for being unhealthy. A previous study shows that they can actually act as environmental pollutants and can infect drinking water.
But hey, how else are you going to make sure your coffee tastes good in the morning?