In 2019, physician Michael Herschel Greger posed a question in his book How Not To Diet: “Animal agriculture has been feeding artificial sweeteners to farm animals since the 1950s, boasting that their addition ‘increases … body weight gain and … optimizes return on investment.’ What about [its impact] in people?” A new study — showing how artificial sweeteners are linked to an increased risk of diabetes and even weight gain in the face of their sugarless promise — appears to have an answer for him.

Artificial sweeteners have long been promoted in health and wellness discourse as the “healthier alternatives” to sugar in everything from soft drinks to desserts. In India, actors like Bipasha Basu, Parineeti Chopra, and recently, Katrina Kaif, have endorsed their usage as a choice for a ‘fitter lifestyle.’ But the new study, published last week in Cell, debunks the mythical claims of these seemingly ‘magical’ sugar substitutes.

The researchers behind the study used a multitude of common artificial sweeteners — including saccharin, sucralose, aspartame, and stevia — to test their impact on 120 healthy adults over a period of two weeks. As it turns out, the sweeteners were found to alter the bacteria that colonize the gut, resulting in a negative impact on glucose tolerance, or the body’s “ability to dispose of a glucose load.” This is essentially a measure of how adept our bodies are at moving sugar from the blood and turning it into muscle and fat. Then an impaired glucose tolerance can increase the risk of developing diabetes and gaining weight.

“This strategy [of using sugar substitutes] has been around for a while as an alternative to [sugar], but our findings beg the question [of] whether they are producing the benefits or not,” noted first author Jotham Suez, a microbiologist at the Johns Hopkins Bloomberg School of Public Health, referencing that “in the past several decades, there has been a massive increase in the prevalence of these metabolic conditions [like diabetes and obesity].” And now, it seems they could indeed be related.

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The present findings are in line with a 2014 study, published in Nature and also led by Suez, which investigated the link between artificial sweeteners and obesity. Conducted on mice, the research culminated in findings analogous to the present one. The researchers noticed obesity-associated metabolic changes in the mice exposed to artificial sweeteners. This, too, was the result of the sweeteners inducing glucose intolerance in mice by altering their gut microbiota. Unfortunately, though, since the study focused on mice and not humans, its findings weren’t taken as seriously, and people continued to use it to cut calories and lose weight.

The present findings make the hazards associated with consuming artificial sweeteners harder to dismiss. As Robert Lustig, a neuroendocrinologist at the University of California, San Francisco, who wasn’t involved in the study, told The Scientist, “The food industry went ballistic [in 2014] because, obviously, this is a major threat. They came up with a zillion reasons why the study was no good… This [new study] is fundamental because it proves causation, not just correlation.”

Another study from 2014 added to the body of research highlighting the negative health outcomes of consuming artificial sweeteners. Its researchers found that most sugar substitutes actually trick our brains into wanting more junk, exposing many of its users to increases calorie intake.

Greger has an explanation for it, “[Artificial sweetener brands] emphasiz[e] that [their products are] hardly even absorbed into the body and ends up in the colon to be eliminated. Therein may lie the problem… [A]rtificial sweeteners can lead to metabolic disturbance [due to] disconnect that develops between the amount of sweetness the brain tastes on the tongue and how much blood sugar actually ends up reaching the brain. Your brain may end up feeling cheated by the artificial sweeteners, figuring you have to consume more and more sweetness in order to get enough calories.”

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Basically, by “disturb[ing] the body’s ability to count calories,” as WebMD puts it, diet foods and drinks sweetened using sugar substitutes can end up facilitating weight gain rather than weight loss. And this, of course, is not counting their contribution to metabolic conditions, and as yet another study found, heart disease and stroke. Moreover, besides being deficient in calories, artificial sweeteners also lack nutrients like vitamins, minerals, antioxidants, and fiber, unlike real sugar.

According to Greger, thankfully, the glucose intolerance induced by sugar substitutes is largely reversible. But he has some bad news, too, “The good news is that after stopping artificial sweeteners, your original balance of gut bacteria can be restored within a matter of weeks. The problem is that we may be exposed without even knowing it… from nondietary sources, such as toothpaste and mouthwash.”

Overall, the oft-touted benefits of artificial sweeteners on people’s health seem rather suspect. It is pertinent to note, though, that in moderation, perhaps, they might still work — especially for people who can’t consume sugar at all. “Even if it is proven in the future that artificial sweeteners are detrimental for the general population, this might not be true in all cases… At the moment, I would not advise against artificial sweeteners per se, but instead, I would stress the importance of a balanced diet and regular exercise,” Inês Cebola from Imperial College London, who wasn’t involved in the present study, had advised.

The takeaway, then, seems to be one of cautious usage. Rather than relying on literature sponsored by artificial sweetener brands — and, of course, endorsements that promote their unquestioning usage — it might be a better idea to consult a physician about one’s individual dietary requirements before buying into fads and replacing sugar completely.