Diet soft drinks are often marketed as a healthier alternative to regular soda, particularly for those watching their sugar intake. However, concerns have been raised regarding the potential impact of diet soft drinks on long-term brain health. This article delves into the possible connection between diet coke consumption and memory loss, examining scientific studies and expert opinions on the matter.
The Role of Artificial Sweeteners
Diet soft drinks often use low-calorie sugar substitutes such as stevia and acesulfame potassium, or Ace-K. Aspartame is another artificial sweetener used in many sugar-free products. It’s made up of two amino acids found naturally in meat, milk and some vegetables. While it contains calories, very little aspartame is needed compared to sugar.
Emerging Research on Artificial Sweeteners and Cognitive Decline
A study published in the September 3, 2025, issue of Neurology, the medical journal of the American Academy of Neurology, shed light on the potential consequences of sugar substitutes for long-term brain health. The study examined seven low- and no-calorie sweeteners and found that people who consumed the highest amounts experienced faster declines in thinking and memory skills compared to those who consumed the lowest amounts. The link was even stronger in people with diabetes.
The artificial sweeteners examined in the study were aspartame, saccharin, acesulfame-K, erythritol, xylitol, sorbitol and tagatose. These are mainly found in ultra-processed foods like flavored water, soda, energy drinks, yogurt and low-calorie desserts.
“Low- and no-calorie sweeteners are often seen as a healthy alternative to sugar, however our findings suggest certain sweeteners may have negative effects on brain health over time,” said study author Claudia Kimie Suemoto, MD, PhD, of the University of São Paulo in Brazil.
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The study included 12,772 adults from across Brazil. Participants completed questionnaires about diet at the start of the study, detailing what they ate and drank over the past year. Researchers divided them into three groups based on the total amount of artificial sweeteners they consumed. The lowest group consumed an average of 20 milligrams per day (mg/day) and the highest group consumed an average of 191 mg/day. For aspartame, this amount is equivalent to one can of diet soda. Sorbitol had the highest consumption, with an average of 64 mg/day.
Participants were given cognitive tests at the start, middle and end of the study to track memory, language and thinking skills over time. After adjusting for factors such as age, sex, high blood pressure and cardiovascular disease, researchers found people who consumed the highest amount of sweeteners showed faster declines in overall thinking and memory skills than those who consumed the lowest amount, with a decline that was 62% faster. This is the equivalent of about 1.6 years of aging. Those in the middle group had a decline that was 35% faster than the lowest group, equivalent to about 1.3 years of aging.
When researchers broke the results down by age, they found that people under the age of 60 who consumed the highest amounts of sweeteners showed faster declines in verbal fluency and overall cognition when compared to those who consumed the lowest amounts. They did not find links in people over 60.
When looking at individual sweeteners, consuming aspartame, saccharin, acesulfame-k, erythritol, sorbitol and xylitol was associated with a faster decline in overall cognition, particularly in memory.
“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.
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A limitation of the study was that not all artificial sweeteners were included. Also, diet information was reported by the participants, who may not have remembered accurately everything they ate.
The Framingham Heart Study
In studies approximately 4,000 participants over the age of 30 from the community-based FHS were examined using Magnetic Resonance Imaging (MRI) and cognitive testing to measure the relationship between beverage intake and brain volumes as well as thinking and memory. These findings appear separately in the journals Alzheimer’s & Dementia and the journal Stroke. “We also found that people drinking diet soda daily were almost three times as likely to develop stroke and dementia.
The researchers point out that preexisting conditions such as cardiovascular disease, diabetes and high blood pressure did not completely explain their findings. For example, people who more frequently consumed diet soda were also more likely to be diabetic, which is thought to increase the risk of dementia.
Expert Opinions on Diet Soda and Brain Health
Jasdeep S. Hundal suggests being mindful about what you drink. “Your brain is literally built from what you put in your body,” he says. “Every bite, sip, or snack can either fuel your brain or slow it down. Many types of diet soda contain aspartame, which is questionable at best,” says Dr. Hundal.
Aspartame: A Closer Look
Aspartame is an artificial sweetener used in many sugar-free products. Researchers have studied the side effects of aspartame for many years. The Food and Drug Administration says aspartame is safe to consume in moderation.
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Animal Studies: Investigating Heritable Effects of Aspartame
Preclinical studies demonstrate that aspartame consumption is associated with neurobehavioral changes including anxiety-like behavior and learning and memory deficits. A recent report demonstrated that aspartame-induced anxiety-like behavior is heritable along the paternal line of descent. However, whether cognitive deficits associated with aspartame consumption such as learning and memory deficits can be heritable was not known.
A mouse model study reported that aspartame consumption via drinking water daily for up to 16 weeks at doses equivalent to only 7-15% of the FDA recommended maximum daily intake value for humans [roughly equivalent to human consumption of 2-4 small (8 oz) diet soda drinks per day] produces significant deficits in spatial learning and memory. Perhaps even more interestingly, the learning and memory deficits are transmitted by aspartame consuming male mice to their male and female offspring.
In this study, adult male C57BL/6 male mice were given free access to drinking water containing aspartame (0.03% or 0.015%), while another set of male mice received plain drinking water (control group). The Y-maze assay was performed at 4, 8, and 12-weeks during the drinking water exposure. During the 13th week, the mice were bred with females purchased from the vendor and maintained on plain drinking water to produce the F1 generation. Following the breeding, and during weeks 14-15 of the exposures, Barnes maze assay was performed. During the 16th week, tail suspension test (TST) was performed. Beginning at approximately 2-months of age, the F1 male and female mice from each drinking water lineage completed the Y-maze, Barnes maze and TST.
During the 16 weeks of aspartame exposure, tests of spatial working memory (Y-maze), spatial learning, memory, and reversal learning (Barnes maze) and learned helplessness (tail suspension test, TST) were performed.
The Y-maze assay, which measures spatial working memory, showed significant effect of drinking water treatment, suggesting poor performance by the two aspartame groups. Aspartame’s effects on working memory were present as early as 4 weeks of exposure and persisted over the entire 12-week duration.
Next, the Barnes maze was used to evaluate spatial learning and memory. Primary error data showed significant effects of session and drinking water treatment. Primary latency data also showed significant effects of session and the drinking water treatment. Thus, although the performance of the mice in all three drinking water groups improved with each successive session, the performance of the mice exposed to aspartame (0.03% or 0.015%) improved slowly compared to that of the mice exposed to plain drinking water.
Mice in all 3 groups used random or serial strategies and not the spatial strategy during session #1 of acquisition of learning, but gradually transitioned to the spatial strategy. The time taken to successfully transition to the spatial strategy was significantly different among the three groups. Thus, although there was a progressive shift toward the spatial search strategy in all 3 drinking water groups, the aspartame groups lagged the plain drinking water group in making this transition during the acquisition of learning phase, suggesting a deficit in spatial learning.
Alternative Beverage Choices for Brain Health
If you’re looking for healthier beverage choices, Dr. Hundal suggests water.
Maintaining Overall Brain Health
According to Dr. Hundal, there are many ways you can keep your brain healthy. Mental activity is also important, especially as you age. This can include reading, doing puzzles or learning something new. Your brain runs on what you eat. Make sure you eat plenty of antioxidants, healthy fats and real nutrients instead of processed foods.