Many people swap sugar for diet soda, “zero” yogurt, or light desserts thinking they are choosing the smarter option for their health. A large new study now suggests that for the brain, that tradeoff may not be so simple.
Researchers in Brazil followed 12,772 adults for about eight years and found that people who consumed the most low- and no-calorie sweeteners had a much faster decline in memory and thinking skills compared with those who consumed the least.
The difference in brain performance was roughly equal to 1.6 extra years of aging in the highest intake group.
The work, published in the journal Neurology, does not prove that sweeteners cause cognitive decline. It does, however, raise serious questions about what regular exposure to these ingredients might mean for midlife brain health.
What the researchers actually measured
At the start of the study, participants with an average age of 52 completed detailed food frequency questionnaires that captured what they ate and drank over the previous year.
From those answers, the team calculated daily intake of seven sweeteners commonly found in ultra-processed foods and drinks. These were aspartame, saccharin, acesulfame K, erythritol, xylitol, sorbitol, and tagatose.
People were then sorted into three groups based on total sweetener intake. The lowest group averaged about 20 milligrams per day.
The highest group averaged 191 milligrams per day, which for aspartame is similar to the amount in one can of diet soda. Sorbitol stood out as the most commonly consumed sweetener, with an average of 64 milligrams per day.
Over the following years, participants completed cognitive tests at the beginning, the middle, and the end of the study. These assessed verbal fluency, working memory, word recall, and processing speed, skills that tend to change with age and are sensitive to early brain problems.
Even after accounting for age, sex, high blood pressure, and cardiovascular disease, people in the highest sweetener group had a global cognitive decline that was 62% faster than those in the lowest group. Those in the middle group declined 35% faster than the lowest group.
Younger adults and people with diabetes hit harder
When researchers looked more closely at age, a clear pattern appeared. Among adults younger than 60, higher intake of sweeteners was linked to steeper drops in verbal fluency and overall cognition. Among adults older than 60, that link did not show up in the data.
The association was also stronger in people with diabetes than in those without the disease. That finding matters because people with diabetes are more likely to use artificial sweeteners in an effort to manage blood sugar while still enjoying sweet tastes.
Looking at the individual sweeteners, higher consumption of aspartame, saccharin, acesulfame K, erythritol, sorbitol, and xylitol was linked with faster overall cognitive decline, especially in memory-related tasks. Tagatose was the one sweetener in the analysis that did not show a measurable relationship with cognitive decline.
Association is not causation, and the debate is heating up
So does this mean every diet soda is quietly “stealing years” from the brain. Not exactly. This study is observational. Participants reported what they ate once at baseline, and their answers are never perfect.
People who choose many diet products may also differ in other ways that affect brain health, including weight, physical activity, sleep, or overall diet quality. Even with careful statistical adjustments, some of those differences can still slip through.
Industry groups have been quick to highlight those caveats. The International Sweeteners Association notes that the work shows only a statistical link, not cause and effect, and points out that all seven sweeteners were combined into a single exposure dominated by sugar alcohols such as sorbitol.
They also stress that intakes of high-intensity sweeteners like aspartame and saccharin stayed well below accepted daily limits and that global regulators including the European Food Safety Authority and the United States Food and Drug Administration continue to consider approved sweeteners safe at current exposure levels.
At the same time, independent health bodies are also taking a more cautious stance.
In 2023, the World Health Organization advised against using non-sugar sweeteners to control body weight, citing a lack of long-term benefit and possible links to type 2 diabetes, cardiovascular disease, and higher mortality, while acknowledging that confounding factors complicate the picture.
An accompanying editorial in Neurology titled “The Dark Side of Sweet” describes these new findings as part of a growing discussion about the neurocognitive consequences of artificial sweeteners and calls for more targeted research on specific compounds such as erythritol.
What this means for everyday choices
For most people, the practical question is simple: what should I do with my morning coffee, my yogurt, or that afternoon energy drink?
Experts involved in the study suggest taking a step back from the idea that the only options are refined sugar or a packet of artificial sweetener. They highlight alternatives such as small amounts of applesauce, honey, maple syrup, coconut sugar, or naturally sweet fruit, while still keeping overall sweetness in the diet in check.
From an ecological point of view, moving away from ultra-processed drinks and snacks also tends to reduce packaging waste and the energy used to make and ship those products.
Diets built around minimally-processed plant foods, similar to Mediterranean or “planetary health” patterns, are associated with lower dementia risk and a smaller environmental footprint at the same time.
None of this means that an occasional diet soda will instantly harm your brain. It does suggest that relying on multiple sweetened products every day, especially in midlife or in the context of diabetes, may not be as harmless as once thought.
At the end of the day, the safest bet for both human and planetary health still leans toward less sweetness overall, more whole foods, and fewer ultra-processed “shortcuts” in the shopping cart.
The study was published in Neurology.
