Low- and no-calorie sweeteners are marketed as a smart swap for sugar, but a growing body of research is raising uncomfortable questions about their long-term effects on the brain. A large, multi-year study published in Neurology in 2024 found that people who consumed the most artificial sweeteners experienced measurably faster cognitive decline than those who consumed the least — a difference roughly equivalent to more than a year and a half of extra brain aging.
The findings, part of the broader conversation about ultra-processed foods and neurological health, are prompting researchers to take a closer look at what these ingredients may be doing beyond replacing calories.
The Study Behind the Headlines
The research, led by Claudia Kimie Suemoto and colleagues at the University of São Paulo, followed 12,772 civil servants enrolled in the Brazilian Longitudinal Study of Adult Health (ELSA-Brasil) for an average of eight years. Participants completed detailed food-frequency questionnaires at the start of the study and repeated cognitive tests measuring memory, verbal fluency, and executive function over time.
After adjusting for age, sex, education, cardiovascular risk factors, and total calorie intake, participants in the highest tertile of sweetener consumption showed a 62% faster rate of global cognitive decline than those in the lowest tertile. The middle group also declined faster than the low-consumption group, hinting at a dose-response relationship.
“Higher consumption of artificial sweeteners was associated with a decline in global cognition equivalent to about 1.6 years of aging,” the authors reported in Neurology.
Which Sweeteners Were Involved
The study looked at seven low- and no-calorie sweeteners commonly found in diet sodas, sugar-free desserts, protein powders, flavored yogurts, and tabletop packets:
- Aspartame (Equal, NutraSweet)
- Saccharin (Sweet’N Low)
- Acesulfame-K (often blended with sucralose)
- Erythritol (a sugar alcohol used in “keto” products)
- Xylitol (common in sugar-free gum)
- Sorbitol (used in sugar-free candies)
- Tagatose
Six of the seven were linked to accelerated decline. Tagatose, a rarer sweetener, was the exception. Notably, stevia — a plant-derived sweetener — was not among those associated with faster cognitive aging in this analysis.
Who Faced the Highest Risk
The association was strongest in two groups: adults under 60 and people with diabetes. That combination matters, because diet drinks and sugar-free products are often marketed heavily to people trying to manage blood sugar or weight — the same population that may be most vulnerable to these effects.
The researchers emphasize the study is observational, meaning it can show an association but not prove that sweeteners cause cognitive decline. Still, the size of the cohort, the length of follow-up, and the consistency of the findings across sweetener types make the signal difficult to dismiss.
How Sweeteners Might Affect the Brain
Scientists are still working out the biological pathways, but several plausible mechanisms have emerged from earlier research:
Gut Microbiome Disruption
A landmark 2022 study in Cell showed that non-nutritive sweeteners can alter the composition of gut bacteria in humans, and those changes were linked to shifts in glucose tolerance. Because the gut and brain communicate through the vagus nerve and immune signaling, microbiome changes may indirectly affect cognition and inflammation.
Vascular and Metabolic Effects
Research published by the American Heart Association has linked artificially sweetened beverages to a higher risk of stroke and dementia in some cohorts. Vascular damage is a known contributor to cognitive decline, so anything that stresses the cardiovascular system may show up years later as memory or thinking changes.
Direct Neurological Signaling
Sweet receptors are not confined to the tongue — they’re also expressed in the gut and, some studies suggest, in the brain. Chronic activation of these receptors by intense non-caloric sweeteners may confuse the body’s reward and satiety pathways in ways researchers are still mapping.
The Bigger Picture: Ultra-Processed Foods and the Brain
Artificial sweeteners rarely travel alone. They tend to appear in ultra-processed foods, which a 2022 study in JAMA Neurology associated with a 28% faster rate of global cognitive decline in adults who got more than 20% of their daily calories from such products. Sorting out how much of the sweetener signal is independent of the broader ultra-processed food pattern is one of the next frontiers.
The World Health Organization added its own note of caution in 2023, advising against using non-sugar sweeteners for long-term weight control, citing potential long-term risks including type 2 diabetes and cardiovascular disease.
What This Doesn’t Say
It’s worth being clear about the study’s limits. Diet was self-reported. The follow-up, while substantial, is still shorter than the decades over which dementia typically develops. And the effect size — while statistically striking — translates to a modest year-and-a-half shift on population-level cognitive scores, not a guarantee that any individual heavy diet-soda drinker will develop dementia.
Randomized controlled trials, which would offer stronger causal evidence, are difficult to run over the timescales relevant to brain aging.
Practical Takeaways
For anyone reviewing their own habits, current evidence suggests a few reasonable considerations:
- Water first. Plain water, sparkling water, and unsweetened tea remain the most consistently recommended beverages by cardiology and nutrition organizations.
- Treat “sugar-free” as processed. A sugar-free label does not automatically mean healthful; it often means an ultra-processed formulation with different additives.
- Consider whole-food sweetness. Fruit, dates, and small amounts of honey or maple syrup deliver sweetness alongside fiber, polyphenols, and micronutrients.
- Watch cumulative exposure. Sweeteners hide in yogurts, protein bars, flavored waters, chewing gum, toothpaste, and children’s medicines. Totals add up.
- Talk to your clinician if you have diabetes. Because the association was strongest in people with diabetes, individual guidance from a doctor or registered dietitian is especially valuable.
Research on artificial sweeteners and the brain is still evolving, and future studies will help clarify which sweeteners, doses, and contexts matter most. In the meantime, findings like these are a useful reminder that “calorie-free” is not the same as “consequence-free.”
Disclosure: This content is for informational purposes only and is not medical advice. Always consult a qualified healthcare provider before making changes to your health regimen.