Replacing sugar with low- or no-calorie sweeteners is a popular way to manage weight. But a new study found relying on certain sugar substitutes may be bad for your brain health.
The study, published Sept. 3 in Neurology, found that people who consumed the highest amounts of six artificial sweeteners also had the greatest declines in thinking and memory, as compared to those who consumed less. Those declines amounted to 1.6 years of additional brain aging.
The results don’t mean someone will notice memory issues immediately after drinking a soda sweetened with aspartame, said study author Claudia Kimie Suemoto, MD, PhD, associate professor of geriatrics at the University of São Paulo Medical School in Brazil.
But for people who consume these sweeteners often, “it does mean their brain may be aging at a quicker pace, which over time could increase the risk of earlier or more severe cognitive impairment,” she told Health.
Suemoto and her colleagues looked at data from 12,772 Brazilian adults who were 52 years old on average. At the beginning of the study, the participants filled out questionnaires about what they usually ate and drank over the previous year.
The research team specifically tracked seven low- and no-calorie sweeteners that show up in common grocery items such as soda, low-calorie desserts, yogurt, or as standalone products:
The scientists then split participants into groups based on their intake of these low- or no-calorie sweeteners:
- Low: about 20 milligrams (mg) per day
- Moderate: about 66 mg per day
- High: about 191 mg per day, about the equivalent of one can of diet soda
Over the span of eight years, the participants underwent various cognitive tests, including verbal fluency (how fast they could pronounce words in a given category), word recall, memory, and information processing speed.
As compared with people who consumed minimal amounts of these low- or no-calorie sweeteners, other participants fared much worse on these cognitive tests, the researchers’ data showed.
On average, the moderate intake group had a 35% faster rate of memory and thinking decline, and a 110% faster rate of verbal fluency decline.
For the high consumption group, their rate of memory and thinking decline was 62% faster, and their verbal fluency decline was 173% faster.
Interestingly, this link between low- or no-calorie sweeteners and worse cognition only existed for people under the age of 60.
“This study is one of the largest to connect several different sweeteners to measurable cognitive decline over time,” Theresa Gentile, MS, RDN, a Brooklyn-based dietitian and spokesperson for the Academy of Nutrition and Dietetics, told Health.
Because the researchers adjusted for diet quality before doing their analysis, all signs point to the fact that “sweeteners themselves add to the risk” of poor brain health, David Perlmutter, MD, a neurologist and fellow of the American College of Nutrition, told Health.
But there wasn’t much of a difference between the sweeteners themselves—tagatose wasn’t associated with cognitive decline at all, the data showed, but the other six sweeteners were.
“We did not see any evidence that one was worse than the other,” Suemoto noted.
The authors of this latest study emphasized their findings don’t prove sweeteners cause cognitive decline. However, experts have some theories about what might be going on.
Your diet is the largest driver of the pathogens that make up your gut microbiome, Rebecca Solch-Ottaiano, PhD, an assistant professor of pharmacology at the Tulane University School of Medicine, told Health.
So consuming more sugar substitutes may change the composition of your gut microbiome and drive inflammation—however, more research is needed. It could simply be that people who eat more artificial sweeteners have a less healthy gut because they don’t eat enough fiber, for example, said Solch-Ottaiano.
Though the exact mechanism isn’t clear, inflammation and microbiome changes can cause the brain’s immune cells (called microglia) to act differently, said Perlmutter. “When microglia shift into that damaging, inflammatory mode, the risk for Alzheimer’s, Parkinson’s, and other forms of cognitive decline rises,” he said.
Research has linked artificially sweetened beverages with higher risks of dementia and stroke. Plus, sucralose—another sugar substitute not included in this study—has been linked to worse memory and executive functioning.
“The weight of evidence suggests at least some sugar substitutes carry real risks,” Thomas Holland, MD, assistant professor with the Rush Institute for Healthy Aging at Rush University, told Health.
In general, people under 60 saw greater risks of cognitive decline and early brain aging when they consumed more artificial sweeteners—but that link was even stronger for people with diabetes, the new study found.
People with diabetes are more likely to consume artificial sweeteners as a substitute for sugar, Suemoto said. That consumption—combined with diabetes’s effect on the body—could explain why these patients are at a higher risk, said Perlmutter.
“Diabetes already stresses metabolism and the microbiome, creating a primed inflammatory state,” he said. “Adding artificial sweeteners seems to make that fire burn hotter, which then fuels microglia to become more damaging in the brain.”
There’s more research that needs to be done, but sugar substitutes may not be as harmless as we think. So Suemoto advised reducing your consumption when you can.
But that doesn’t necessarily mean it’s better to swap these no- and low-calorie options for added sugar—plenty of research has tied sugar intake to dementia and a host of other health issues.
It’s challenging, but the best course of action is to retrain your tastebuds to enjoy less sweet foods, Perlmutter said.
“The real goal should be less sweetness overall, less processed food, and more fiber-rich whole foods to support gut bacteria and brain health,” he added.
But when you need a substitute, try less-processed sweeteners such as stevia or tagatose, Perlmutter recommended.
