Most artificial sweeteners on the market are considered safe at typical consumption levels, but growing research has raised legitimate concerns about several of them. The sweeteners with the most evidence of potential harm are saccharin, sucralose, and aspartame, each flagged for different reasons ranging from gut disruption to possible cancer risk. Sugar alcohols like xylitol have also come under scrutiny for cardiovascular effects. Here’s what the evidence actually shows for each one.
Sucralose and Gut Health
Sucralose (sold as Splenda) is one of the most widely used artificial sweeteners, and it’s also one of the most studied in recent years. A 2023 study found that sucralose-6-acetate, both a contaminant in commercial sucralose and a compound your body produces when it breaks sucralose down, can damage DNA in human blood cells. The same research found that sucralose damaged the gut lining (sometimes called “leaky gut”) and increased the activity of genes linked to oxidative stress, inflammation, and cancer in gut cells.
Separately, a controlled trial published in the journal Cell found that sucralose significantly impaired glycemic responses in healthy volunteers, meaning their bodies handled blood sugar less effectively after consuming it. This effect was driven by changes to gut bacteria, and researchers confirmed the link was causal by transplanting gut microbiomes from sucralose-consuming humans into mice, which then developed glucose intolerance. For a sweetener often chosen by people trying to manage blood sugar, that finding is particularly important.
Aspartame and Cancer Risk
Aspartame (found in Diet Coke, Equal, and thousands of other products) made headlines in 2023 when the International Agency for Research on Cancer classified it as “possibly carcinogenic to humans” (Group 2B). That classification was based on limited evidence linking aspartame to liver cancer. It’s worth understanding what Group 2B means: it’s the same category as aloe vera extract and pickled vegetables. The evidence suggests a possible link, not a proven one.
The FDA maintained aspartame’s safety status after the IARC announcement, keeping its acceptable daily intake at 50 mg per kilogram of body weight per day. For a 150-pound person, that translates to roughly 75 packets of sweetener or about 18 cans of diet soda daily. Most people consume nowhere near that amount. Still, the IARC classification was notable because it came from the world’s leading cancer research body, and it signals that long-term, high-consumption patterns deserve more attention.
Saccharin and Blood Sugar
Saccharin (Sweet’N Low) was once the most controversial sweetener on the market. In the 1970s, studies linked it to bladder cancer in rats, leading to warning labels that stayed on products until 2000. Those findings were later deemed irrelevant to humans because the cancer mechanism was specific to rat biology.
The more current concern with saccharin is metabolic. The same Cell study that flagged sucralose found that saccharin also significantly impaired glycemic responses in healthy people by altering gut bacteria. Of the four sweeteners tested (aspartame, saccharin, sucralose, and stevia), saccharin and sucralose were the two that measurably disrupted blood sugar regulation. If you’re using saccharin specifically to avoid the blood sugar effects of real sugar, this research suggests it may partly undermine that goal.
Xylitol and Heart Risk
Xylitol is a sugar alcohol, not technically an artificial sweetener, but it’s used in many of the same products: sugar-free gum, mints, toothpaste, and “keto-friendly” snacks. A study highlighted by the National Institutes of Health found that people with the highest blood levels of xylitol were about 50% more likely to experience cardiovascular events like heart attacks and strokes over a three-year period compared to those with the lowest levels.
This doesn’t mean chewing a piece of xylitol gum puts you at risk. Blood levels in the study reflected higher overall exposure, and the research was observational, meaning it identified a correlation rather than proving xylitol directly causes heart problems. But for people consuming large amounts of xylitol-sweetened products daily, especially those already at elevated cardiovascular risk, it’s a finding worth paying attention to.
Stevia, Neotame, and Advantame
Not all sugar substitutes carry the same concerns. In the Cell study on gut bacteria, stevia did not significantly impair glucose tolerance the way saccharin and sucralose did. It still altered the microbiome to some degree (all four tested sweeteners did), but without the measurable blood sugar consequences.
Neotame and advantame are newer, extremely potent sweeteners used in tiny quantities. Advantame has been tested extensively in animals and a human clinical trial, showing no systemic toxicity. The predicted human intake under normal use is roughly 20,000 to 70,000 times lower than the doses that caused any notable effects in animal studies. These sweeteners simply haven’t generated the red flags that sucralose, saccharin, and aspartame have, though they also haven’t been consumed by billions of people over decades yet.
The WHO’s Position on All of Them
In 2023, the World Health Organization recommended against using any non-sugar sweeteners for weight control or to reduce the risk of chronic disease. Their review of the evidence suggested potential long-term risks including increased likelihood of type 2 diabetes, cardiovascular disease, and mortality in adults. The WHO labeled this a conditional recommendation, acknowledging that the observed links might be partly explained by the fact that people who use more artificial sweeteners often have other risk factors. But their overall message was clear: swapping sugar for artificial sweeteners is not the health strategy many people assume it is.
How These Sweeteners Affect Your Body
The gut microbiome disruption is probably the most broadly relevant concern across multiple sweeteners. Your gut bacteria influence everything from immune function to mood, and the evidence now shows that aspartame, saccharin, sucralose, and stevia all functionally alter the microbiome. The practical consequences vary by sweetener and by individual, but the notion that these compounds pass through your body without any biological effect has been convincingly disproven.
There’s also an ongoing debate about whether tasting something intensely sweet without consuming actual calories confuses your body’s metabolic signaling. When you taste sweetness, your body may begin preparing to process incoming sugar by releasing small amounts of insulin, a phenomenon called the cephalic phase insulin response. If no sugar arrives, the concern is that this mismatch could, over time, contribute to metabolic dysregulation. The research on this mechanism is still evolving, and individual responses vary considerably.
Where These Sweeteners Hide
Artificial sweeteners aren’t just in diet sodas and pink packets. They show up in yogurt, protein bars, flavored water, chewing gum, cough drops, toothpaste, and even some medications. Products labeled “sugar-free,” “zero sugar,” “light,” or “no added sugar” almost always contain one or more of these compounds. Check ingredient lists for names like acesulfame potassium (Ace-K), sucralose, aspartame, saccharin, and sugar alcohols ending in “-ol” (xylitol, erythritol, sorbitol). If you’re trying to reduce your exposure, reading labels is the only reliable strategy, since many products marketed as healthy use these sweeteners extensively.