For a lot of us, including me, diet soda seems almost miraculous: it’s calorie-free and offers a mostly guilt-free way to enjoy something like a soft drink.
However, ever since diet sodas and similar sugar-free products hit the market, some folks have raised eyebrows about the non-nutritive sweeteners they contain, which include artificial options like sucralose and aspartame, along with more natural ones like stevia. Some of these fears seem silly—like an infamous email chain back in the 2000s that inaccurately claimed aspartame was initially developed as ant poison. Yet, recent studies have called into question the idea that these sweeteners are entirely safe.
Just this month, for example, researchers in Chile discovered that sucralose and stevia might change the gut microbiome and negatively affect genes tied to metabolism and inflammation in mice. These alterations could even be passed on to future generations. Additionally, a study from last September found a correlation between higher consumption of low- or no-calorie sweeteners in older adults and accelerated cognitive decline. Another study published in May 2025 identified a link between aspartame and worsening atherosclerosis, a significant factor for cardiovascular disease.
Although these studies do have their limitations (after all, mice aren’t exactly representative of humans), it raises reasonable doubts about whether these sweeteners could have hidden health drawbacks. So, in this week’s Giz Asks, we sought insights from researchers and nutrition specialists to discuss the current understanding of these sweeteners and whether it might be wise to reduce our intake. Their responses have been edited for clarity.
Yihai Cao
A cancer researcher and molecular biologist at the Karolinska Institute in Sweden. Cao also co-authored the study on aspartame from May 2025.
From a scientific standpoint, there is evidence suggesting that artificial sweeteners may not be as beneficial as previously thought.
In our research last year, we found that aspartame can increase insulin levels. While we only conducted this study on animals, I suspect humans might respond similarly. This elevation in insulin could lead to physiological changes and potentially trigger certain diseases, like cardiovascular issues, due to inflammation.
The findings from the recent study on gut microbiota don’t really surprise me. Anything we consume can affect our gut’s microorganisms, which in turn can impact tissue health. This isn’t just about artificial sweeteners; it applies to any food. If someone favors a certain type of food, their gut bacteria composition can change based on those dietary choices. Over time, these changes might even affect the next generation, depending on their eating habits and lifestyles.
Our microbiome is constantly changing. There are beneficial and harmful bacteria, but we don’t have a solid agreement on what defines a healthy balance. I suppose there’s a threshold; if microbiome changes stay within it, that’s fine. But if they stray too far, trouble could follow.
I’m cautious about asserting too much since I didn’t run that experiment, but I do believe our lifestyles play a significant role, whether it’s through our exercise routines or dietary choices.
Jotham Suez
A molecular microbiologist at Johns Hopkins University focusing on microbiomes. Suez has conducted multiple studies on non-nutritive sweeteners.
Realistically, it’s wise to limit artificial sweetener intake—if people can manage it without substituting them for sugary foods and beverages. Excess sugar is clearly associated with increased risks of obesity, diabetes, and heart disease, which is why many turn to artificial sweeteners in the first place. However, there isn’t strong evidence showing that these sweeteners lead to consistent weight loss or improved blood sugar control; in fact, they might contribute to the very issues they’re meant to avert.
There’s been considerable research regarding artificial sweeteners’ effects in animal models, with most studies indicating adverse outcomes. However, human studies tend to show that while higher consumption correlates with increased risks of diabetes and heart disease, it’s less clear whether sweeteners are the direct cause. Some studies indicate that sweeteners can lead to weight gain and impaired blood sugar control, while others find them neutral.
New research suggests that individual differences in gut microbiome might explain why some people experience poorer blood sugar control after consuming artificial sweeteners. It appears that certain gut bacteria are more significantly affected by these sweeteners, leading to disrupted glycemic control, a diabetes risk factor. This points to variability in how individuals respond to these sweeteners.
More definitive research is necessary to better understand artificial sweeteners’ health impacts, and we still can’t predict who might be adversely affected. Still, given that they’re not essential to our diet and their potential risks, it might be wise to limit consumption.
Christopher Gardner
A dietary researcher at the Stanford Prevention Research Center and lead author of a scientific advisory statement on artificial sweeteners.
Just to start, I’m not a fan of sugar substitutes or even sugar itself. The whole situation seems off balance; we consume far too much sugar, and rather than substituting it, we should aim for real food. Nevertheless, if someone struggles with cutting sugar, could a sugar substitute be beneficial? The evidence on that is quite varied. Years ago, I authored a report for the American Heart Association, stating that the available data was rather poor, lacking sufficient quality studies.
Regarding the recent mouse study, I have concerns. They compared water to sucralose and stevia, which strikes me as questionable. If sucralose and stevia are meant to substitute sugar, shouldn’t we also incorporate sugar into the comparison? Water alone doesn’t represent the typical scenario.
I understand the choice of water for comparison since it’s safe. Comparing sweeteners to just water seems to sidestep the bigger issue of whether they’re actually less healthy than sugar, which is what consumers care about.
Also, comparing the effects on mice over generations is something you can’t ethically do with people, which raises its own questions about applicability.
To study this in humans, we have to tread carefully. We can’t ethically expose people to potentially harmful levels of sugar substitutes; that wouldn’t allow for effective recruitment. Instead, we could ask participants to replace sugar with sucralose, stevia, or water to assess which works better. However, this is tricky for other reasons too; swapping sugar in a diet isn’t straightforward, especially when considering what you can make with sweeteners versus sugar’s cooking properties.
A variety of studies across different participant groups and durations are necessary to evaluate this issue comprehensively, which is why mouse studies are often preferred for basic research. Mice eliminate the human error factor; they’re always consistent, whereas humans can vary significantly in reporting their diets. So while the current study design doesn’t impress me much, it might still contribute to our understanding in the future.
On a personal note, I avoid sucralose and stevia as much as possible, though I acknowledge I still consume an excess of sugar.
Andrew Kau
An associate professor at Washington University School of Medicine focusing on allergy and immunology.
Artificial sweeteners are prevalent in everyday foods, drinks, and supplements. On the face of it, they seem ideal—these additives mimic sugar but have minimal calories. In my student days, I often opted for diet sodas, believing they would aid in weight management.
However, studies demonstrating that artificial sweeteners lead to lasting weight loss are conflicting at best. They might also contribute to diabetes and heart disease development, though further research is needed. The long-term effects of these sweeteners may alter gut microbiota, which play an essential role in our health and metabolism. There’s evidence that prolonged exposure to these sweeteners can disrupt beneficial bacterial functions, with some studies suggesting a hereditary aspect to these changes. Still, given that most research relies on animal subjects, I remain skeptical about any purported health benefits of artificial sweeteners.
That said, I think our concern should extend to food additives in general, not just artificial sweeteners. Many processed foods contain a variety of chemical additives that enhance taste and shelf life, all of which also impact gut bacteria, warranting more investigation into their long-term effects.
Ultimately, I don’t believe we need to demonize artificial sweeteners; they certainly have a role in our diets—I just don’t think it should be a prominent one (I do enjoy my sugar-free gum!). We should prioritize eating unprocessed, nutritious foods. Moreover, we need to reassess how much of these additives is appropriate for regular consumption. Careful food choices, guided by substantial long-term studies on dietary additives, are essential.
Laura Bosman
An in-house nutrition expert at the European Food Information Council, a nonprofit dedicated to providing science-based information about food and health.
Do we need to eliminate artificial sweeteners? The short answer is no, but recent studies remind us that the science surrounding non-nutritive sweeteners is still developing, and careful interpretation of new findings is essential.
Recently, a study suggested that non-nutritive sweeteners like sucralose and stevia might negatively affect gut microbiomes and influence genes connected to metabolism and inflammation. This raises pertinent scientific questions. However, it’s crucial to realize what this research can inform us—and what it cannot. Such studies often assess biological markers rather than real-life health outcomes for people, such as type 2 diabetes or heart disease. Results from animal research don’t always directly translate to humans.
Animal studies often serve as initial steps in the evidence-gathering process. While valuable in understanding potential biological mechanisms, they don’t offer direct predictions about human outcomes. Human diets are more complex, exposures differ vastly, and each gut microbiome is unique. To visualize this, think of animal studies as puzzle pieces; while they add some context, they don’t complete the entire picture. For changes in public health guidance to occur, we need consistent, well-designed human studies demonstrating clear impacts at normal consumption levels.
When we consider broader human research, regulatory bodies like the European Food Safety Authority (EFSA) have determined repeatedly that approved sweeteners are safe within specified acceptable daily intake levels, which have considerable safety margins. Evidence shows that within these limits, sweeteners do not lead to sugar cravings or diseases like cancer or diabetes in humans.
However, the World Health Organization (WHO) has suggested that non-sugar sweeteners shouldn’t be relied upon for weight management or mitigating risks of certain diseases, especially in individuals without type 2 diabetes. This recommendation is about effectiveness, not safety, and it’s still a subject of scientific debate. Short-term studies have linked higher consumption of non-sugar sweeteners to lower body weight, but longer observational studies have associated their higher intakes with weight gain and elevated diabetes risk—though these types of studies are harder to interpret.
Unlike nutrients like carbohydrates or fats, there are no specific intake recommendations for food additives like sweeteners. Their potential advantages largely depend on context; factors such as a person’s weight, whether sweeteners replace sugar in their diet, and how consistently that substitution occurs all play a role.
Current evidence generally supports the idea that sweeteners can assist some individuals in losing weight and may help those with diabetes manage blood glucose levels. However, there’s not enough evidence to recommend a widespread, long-term shift away from sugar across all products, and non-sugar sweetened drinks shouldn’t be considered substitutes for water. Gradually adjusting to less sweet tastes could be a helpful strategy for reducing sugar in the diet, with low-calorie sweeteners serving as one tool in that process.
Ultimately, the strongest evidence suggests that overall diet quality is what truly influences health. Sweeteners might fit into this, but moderation and context matter.
