Swapping sugar for a “diet” drink or a low-calorie dessert can feel like the smarter choice. For many people, it is part of the daily routine, right next to the morning coffee, the yogurt cup, or that flavored water grabbed on the way to work.
But a large new study from Brazil suggests the brain-health story may be more complicated. Researchers found that people who consumed the highest amounts of several common low- and no-calorie sweeteners had faster declines in memory and thinking over about eight years, especially adults under 60 and people with diabetes.
The study found a link, not proof of cause and effect, but it raises a very practical question. Are we leaning too hard on sweetness, even when it comes without sugar?
What the study found
The research, published in the medical journal “Neurology,” followed 12,772 adults across Brazil. Participants were 52 years old on average, and researchers tracked them for about eight years using diet questionnaires and cognitive tests.
The highest intake group consumed an average of 191 milligrams of artificial sweeteners per day. For aspartame, the American Academy of Neurology said that is roughly equal to the amount found in one can of diet soda.
After adjusting for factors such as age, sex, high blood pressure, and cardiovascular disease, researchers found that the highest intake group had a 62 percent faster decline in overall thinking and memory than the lowest intake group. That difference was described as roughly equal to 1.6 years of brain aging.
The sweeteners involved
The study looked at seven sweeteners that are common in ultra-processed foods and drinks. They included aspartame, saccharin, acesulfame-K, erythritol, xylitol, sorbitol, and tagatose.
These ingredients are not only found in diet soda. They can also appear in flavored waters, energy drinks, low-calorie yogurts, protein snacks, sugar-free gum, and desserts marketed as lighter choices. In everyday life, that can add up quietly.
When the researchers examined individual sweeteners, higher intake of aspartame, saccharin, acesulfame-K, erythritol, sorbitol, and xylitol was linked to faster decline in overall cognition, especially memory. Tagatose was the only sweetener in the study that was not linked to cognitive decline.
Why age and diabetes mattered
One of the most striking findings was the age pattern. Among people under 60, higher sweetener intake was linked to faster decline in verbal fluency and overall cognitive performance. Among adults over 60, researchers did not find a significant association.
The link was also stronger in people with diabetes. That matters because many people with diabetes use sugar substitutes to help manage blood sugar while still keeping sweet foods and drinks in their routine.
Claudia Kimie Suemoto, MD, PhD, of the University of São Paulo, put it simply. “Low- and no-calorie sweeteners are often seen as a healthy alternative to sugar,” she said. But the findings suggest some may have negative effects on brain health over time.
This does not mean panic
Here is the key nuance. The study does not prove that artificial sweeteners caused the faster cognitive decline. It shows an association, which means other factors could still be part of the picture.
Diet was also self-reported, so participants may not have remembered everything they ate and drank with perfect accuracy. The study also did not include every sweetener on the market, which means it should not be treated as the final word on the entire category.
Still, the results fit into a broader shift in how experts talk about sugar substitutes. In 2023, the World Health Organization advised against using non-sugar sweeteners for weight control or for reducing the risk of chronic diseases, although that recommendation was conditional.
What readers should keep in mind
This is not a green light to go back to heavy sugar intake. High added sugar intake has its own well-known health concerns, especially for metabolic health, dental health, and long-term disease risk.
In practical terms, the smartest move may be less dramatic and more realistic. Check labels, notice how many “sugar-free” or “zero” products show up in a normal day, and try to reduce the overall need for intense sweetness.
For people with diabetes, the takeaway is especially important. Do not make sudden changes to your diet or medication plan based on one study. A doctor or registered dietitian can help balance blood sugar goals with long-term eating habits that support the brain, heart, and overall health.
A better path forward
The bigger lesson may be that “low-calorie” does not automatically mean “better for every part of the body.” A diet drink at lunch, a sugar-free yogurt in the afternoon, and a low-calorie dessert after dinner may look harmless on their own, but the pattern is what researchers are now trying to understand.
Fruit, unsweetened yogurt, nuts, water, sparkling water without sweeteners, and meals built around fiber-rich whole foods are not as flashy as “zero sugar” packaging. But for the most part, they give the body more than just a sweet taste.
At the end of the day, this study is a reminder to look beyond the front label. The brain may care about the small daily choices we barely notice.
The study was published on Neurology.
