Sugar substitutes, once hailed as silver bullets that make it okay to take your coffee extra-sweet, have been dealt another blow. A new study published in the journal Molecules calls out six sugar substitutes for causing strange DNA damage in gut bacteria or just straight-up killing tiny, helpful microorganisms in the body. And these chemical sweeteners are more common than you think: They’re found in Splenda, diet sodas, and ten widely available sports supplements.

This study’s list of disastrous agents for your microbiome is pretty damning: aspartame, sucralose, saccharine, neotame, advantame, and acesulfame potassium-K (Ace-K) all made the cut. All of these sweeteners are FDA-approved, but some will sound more familiar than others — and, according to the researchers’ experiments on glowing bacteria fed these sweeteners, some are also more dangerous.

“The six sweeteners that are FDA approved are the most common in soft drinks and as food additives,” Ariel Kushmaro, Ph.D., a senior lecturer at Ben Gurion University’s department of biotechnology engineering tells Inverse. “We demonstrated the toxicity for bacteria and some hints for the mechanisms.”

tab
Tab was one of the first low calorie sodas ever made, and still uses saccharin. Saccharin has been green-lighted by the FDA, but this research suggests that it can have some harmful effects

While these chemicals all basically taste the same, the damage they do to gut bacteria actually differs a lot, depending on your artificial sweetener of choice.

Different Sweeteners, Different Threats

Kushmaro’s experiment used a bioluminescence technique to literally set off warning lights that illuminated the dangers of these artificial sweeteners to bacteria — in particular, E. coli, a bacteria present in the human gut. The team genetically engineered several strains of E. coli to light up if they were exposed to something dangerous. Importantly, each individual strain was engineered to respond to a different type of threat. For example, if the sweetener being tested caused DNA damage (a “genotoxic” effect), it would cause one particular strain of bacteria to glow. If a different sweetener was cytotoxic (meaning it could kill cells) a different strain of bacteria would light up.

In 2013, Coke ran a series of ads defending aspartame, an ingredient in Diet Coke

This test revealed that saccharin caused the most widespread damage, triggering both genotoxic and cytotoxic effects in E. coli.

Not many soft drinks use saccharin these days (Tab, which uses calcium saccharin, is a popular exception), but FDA documents say that it can be safely used in drinks regardless. But this research suggests that, at least for gut bacteria, saccharin might not be so safe after all.

The experiments also revealed that aspartame and Ace-K cause DNA damage in E. coli. Unlike saccharin, both of these are relatively common. For example, Coke Zero is sweetened with a mixture of aspartame and Ace-K, as are orange and strawberry Fanta.

What’s worrying is that Ace-K isn’t just found in diet soda. It’s also often used as a sweetener in sports supplements, according to Kushmaro. This led him to test the E. coli with ten different sports supplements (which the authors don’t name in the paper) that contained either Ace-K or sucralose, another chemical on the list. They found that each of these supplements demonstrated similar toxic effects on the E. coli as the sweeteners themselves, but it’s hard to tell what’s happening in detail because of the many conflicting components of most sports-performance concoctions.

Though Kushmaro’s observations might be serious enough to make you steer clear of artificial sweetener, he points out that most people probably don’t add enough of sweetener to a cup of coffee, or drink enough diet Fanta (his study points to 1 milligram per milliliter as the toxic level), to cause widespread microbiota damage.

“The human exposure is probably less than several milligrams of artificial sweeteners per milliliter, but it is every day and often several times a day,” he adds.

Though these sweeteners pose seriously risks, it’s not likely that they’re going anywhere anytime soon, says Kushmaro: “The food industry is very strong and will claim that these products are safe.”