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Study Shows Exciting New Way that Diet Soda Can Make You Feel Like Shit

Turns out artificial sweeteners can mess with the delicate balance of your juicy little gut bacteria.
Photo: Getty Images/Karimala

There’s something disconcerting about diet soda. While it might taste OK, and can satisfy a craving for something sweet and bubbly to sip alongside your burger or slice, a casual look at its ingredients list is not for the faint of heart. Diet Coke, for example, warns that its product contains phenylalanine, without defining what the hell that is, anyway, and also discloses that the soda contains GMO ingredients. And then there’s aspartame, a common artificial sweetener that’s marketed under the brand names Nutrasweet and Equal.


I’ve held a deep-seated mistrust of artificial sweeteners ever since I was a child, when my paternal grandfather used to stir pink-packeted Sweet’N Low into his coffee and tea with reckless abandon. My health-food-pushing mom always frowned on this practice, warning us kids that the packets contained poison that could cause cancer. While that’s a common belief, cancer groups including the NIH’s National Cancer Institute claim that there’s no evidence to support the theory, and major brands of aspartame, saccharin, and sucralose are all approved by the FDA.

While the health effects of artificial sweeteners might remain unclear, new evidence suggests that one way they could be harming us is by damaging the community of microbes in our guts. In a new paper published by Molecules and reported by ScienceDaily, a team of researchers from universities in Israel and Singapore found that small doses of the six most common sweeteners—aspartame, sucralose, saccharin, neotame, advantame, and acesulfame potassium-k—were toxic to E. coli, one of the most populous bacteria found in the digestive system.

Because artificial sweeteners cannot be broken down by the body, they are calorie-free, and in theory, should pass through our systems without doing a whole lot. But sweeteners do encounter our gut microbes, a complex community of organisms such as lactobacillus and bifido that you might recognize from your yogurt or kefir label. In the study, the scientists examined bioluminescent E. coli bacteria, which light up when they detect toxins ( whaaa?) and therefore “act as a sensing model representative of the complex microbial system," professor Ariel Kushmaro, one of the study’s authors, told ScienceDaily. When exposed to the sweeteners, as well as ten sports supplements and drinks that contain them, the E. coli bacteria glowed, indicating that they had encountered a toxic substance.


"This is further evidence that consumption of artificial sweeteners adversely affects gut microbial activity which can cause a wide range of health issues," Kushmaro said.

But according to Dr. Purna C. Kashyap, a human microbiome expert at Minnesota’s Mayo Clinic, the study wasn’t without its limitations. For one thing, it only examined one type of bacteria; anywhere from 500 to 1,000 species live in the gut, and this study wouldn’t necessarily elucidate how the sweeteners affect those other types. Secondly, the study looked at isolated, “in vitro” bacteria outside their native environment of a human gut (or even a lab animal’s gut). These types of studies, Kashyap told MUNCHIES, can be helpful starting points for research, but they are not strong enough to draw solid conclusions from.

“It’s a big leap from what happens in vitro to what happens inside our guts,” he said.

Preferably, Kashyap said, a robust study should administer the “offending agent”—in this case, the artificial sweetener—to a group of people, and then measure any changes in the microbiota, or community of organisms in the gut. Another technique scientists use is to take a sample of a human’s gut microbiota and implant it in a genetically altered, germ-free mouse, whose reaction to its new microbiome can be a good indication of problems or toxicity. The study published in Molecules, however, employed neither technique.


Still, Kashyap said, there’s already a body of evidence demonstrating the dangers of artificial sweeteners to the microbiome. He cited a 2014 Nature study, “Artificial sweeteners induce glucose intolerance by altering the gut microbiota,” which used sweetener-fed mice and humans to demonstrate acquired glucose intolerance; basically, both the animals and the people showed a higher risk of developing diabetes as a result of consuming artificial sweeteners.

Kashyap noted that each person possesses a unique microbiome, and that while some might be susceptible to the effects of consuming artificial sweeteners, others might be totally fine. But for him personally, diet sodas are a no-go.

“I have given up all diet soda,” he said. “If I do have a soda, I’ll have the one which has sugar. It’s not good for you either, but it’s a naturally occurring sweetener, and I’d rather have one of those every three months than to have a diet soda at all.”

Additionally, Kashyap observed, those of us in the West are already at a pretty big disadvantage when it comes to our guts. Our huge intake of processed, packaged foods and over-reliance on antibiotics has weakened our microbiota, making us more susceptible to harm from artificial sweeteners and other food additives including “natural flavors” and emulsifiers. Therefore, it’s a doubly good idea to lay off the diet soda.

“I have enough vices already,” Kashyap said. “This one seems like an unnecessary risk.”