It’s the ultimate soda debate: Are you regular or diet?
A recent study in the American Academy of Neurology found that several big-name sugar substitutes may be linked to faster declines in memory and cognitive skills — particularly in people under the age of 60 and with diabetes.
Artificial sweeteners such as erythritol (Truvia), aspartame (Equal) and saccharin (Sweet N’ Low) are widely used in products advertised as “sugar-free” or “diet.” In the U.S., they are regulated by the Food and Drug Administration and technically taste sweeter than regular sugar, but have fewer calories and are less likely to raise blood sugar levels, which is why they’re commonly suggested as a substitute for sugar in diets for people with diabetes.
The study, published in September 2025, focused on seven artificial sweeteners, including acesulfame-K, sorbitol, tagatose and xylitol.
Researchers followed 12,772 adults, with a median age of 52, over eight years. Participants reported their own diet data, focusing on seven sweeteners commonly found in ultra-processed foods and drinks, including flavored water, soda, energy drinks, yogurt and some low-calorie desserts.
What The Study Found
Researchers found that participants who consumed larger amounts of sugar substitutes experienced faster declines in overall thinking and memory skills than those who consumed much smaller amounts.
People with the highest consumption saw a 62% faster rate of cognitive decline than those with the lowest consumption. Those in the highest consumption group were also more likely to report they had diabetes, which researchers say may partly explain the stronger effect in that group. That rate is equivalent to roughly 1 1/2 years of brain aging.
The middle group saw a 35% faster rate than the lowest group, which is roughly 1 year and 3 months of aging.
The link was strongest among participants younger than 60, who saw faster declines in verbal fluency and overall cognition than those over 60.
“This does not mean that cognitive decline started before age 60,” Claudia Suemoto, the lead expert on the study at the Universidade de São Paulo, Brazil, told HuffPost. “Our findings suggest that midlife may represent an important window during which long-term dietary exposures could influence brain aging.”
What The Study Doesn’t Tell Us
The study was observational and does note in its findings that “it could not establish that the sweeteners caused those changes,” nor did the study include every artificial sweetener on the market. One of the artificial sweeteners included, tagatose, was also not linked to any cognitive decline in the participants. This doesn’t necessarily mean tagatose is safer than other sweeteners; it’s unclear whether participants reported using less tagatose.
“The study relies on a self-reported method for dietary data collected only once at baseline 8 years ago, which is often inaccurate, can introduce significant bias, and does not consider changes in dietary habits and product formulations over time,” the International Sweeteners Association said in response to the study in September. “The safety of low/no calorie sweeteners has been consistently confirmed by leading global health authorities.”
Even though researchers cannot confidently identify which mechanism explains the association, Suemoto, now a professor at the Kate Marmion School of Public Health, University of Texas at San Antonio, told HuffPost that neuroinflammation could be the link between the two and something to study further.
“Experimental studies have shown that some artificial sweeteners can induce inflammatory responses in the brain, and neuroinflammation is recognized as an early process involved in both Alzheimer’s disease and vascular cognitive impairment,” she said. “Another plausible mechanism is disruption of the gut microbiota, which could influence brain health through the gut-brain axis and potentially affect blood-brain barrier integrity.”
However, Clifford Segil, DO, a neurologist at Providence Saint John’s Health Center in Santa Monica, California, told HuffPost it’s unlikely to be neuroinflammation, but maybe related to the brain’s high energy demands.
“A substitute sugar that is not the brain’s natural sugars can affect the brain,” he said. “Energy dressed up as a sugar substitute doesn’t work the same in your brain as any sugar.”
Stefania Pelfini la Waziya via Getty Images
Segil also argued that more research needs to be done before anyone should panic over consuming alternative sweeteners, especially if they are recommended to by their doctors.
“There’s no guarantee that taking [them] will result in memory loss,” he said. “A healthy diet is important, especially as we age.”
Should You Ditch Diet Soda?
The concern isn’t limited to soda, either.
“Everyone’s taking these substitute sugars,” Segil said, noting that people on GLP-1 medications are especially likely to encounter them in protein bars. These sweeteners are often listed under “sugar alcohols” rather than their more recognizable sweetener names on nutrition labels.
“This is a ‘moderate it’ moment, not a ‘throw it all out’ one,” Keri Gans, a nutritionist and author in New York City, told HuffPost. “One diet soda a day is not a reason to panic or assume harm. The study may prompt people to consider their overall intake, but it does not establish that a specific amount causes cognitive decline.”
According to Suemoto, more research is needed before any major decisions are made.
“While we found links to cognitive decline for middle-aged people both with and without diabetes, people with diabetes are more likely to use artificial sweeteners as sugar substitutes,” Suemoto said. “More research is needed to confirm our findings and to investigate if other refined sugar alternatives, such as applesauce, honey, maple syrup or coconut sugar, may be effective alternatives.”
For people with diabetes, Gans advises, “A better approach is to reduce overall sweetness when possible and to individualize the choice of the sweetener.”