For years I ordered the diet one and felt faintly virtuous about it. No sugar, no calories, no spike, no guilt. That was the whole pitch, and I bought it, the way most of us bought it, because the alternative was the thing we were all told to fear.
So a study that tracked nearly thirteen thousand people for eight years stopped me cold, and not because its headline number is enormous. It is because of who the decline clustered in. The group that slid fastest was the one handed these sweeteners as the responsible choice in the first place: people with diabetes.
The research, published in the journal Neurology by a team led by Claudia Kimie Suemoto at the University of São Paulo, drew on ELSA-Brasil, a prospective cohort of 12,772 adults with an average age of 52 at the start. Researchers logged what people ate and drank, then measured memory and thinking over roughly eight years. The people consuming the most artificial sweeteners, about 191 milligrams a day, roughly what sits in a single can of diet soda, declined 62 percent faster on cognitive tests than the people consuming the least. The American Academy of Neurology put a number on it: about 1.6 extra years of brain aging. The middle group, no saints either, ran 35 percent faster, roughly 1.3 years.
Six of the seven sweeteners were in on it: aspartame, saccharin, acesulfame-K, erythritol, sorbitol, and xylitol. Only tagatose, the one almost nobody actually eats, came out clean.
Now sit with the diabetes part, because it is the part that should make somebody uncomfortable. Diabetics are the exact population told, by doctors and dietitians and the side of the can, that these compounds are the safe lane, the swap that lets you have something sweet without wrecking your glucose. In this data they were the ones whose thinking slid fastest. The effect also showed up in people under 60 and faded in people over 60, which sounds reassuring until you turn it over. It means the damage, if it is damage, seems to land in midlife, the decades when people reach for sweeteners hardest to lose weight or control sugar, and when the brain still has the most road left to lose.
The molecule was never supposed to reach the brain
So the question I could not put down: how does a molecule with no calories, one built to pass through you untouched, reach the brain at all? That is the entire selling point of a non-nutritive sweetener. Your body is not supposed to metabolize it. It is supposed to be a ghost.
Except it isn’t, and the likeliest reason is your gut. These compounds do not float past your microbiome, they land on it. In a 2022 randomized trial published in Cell, Weizmann Institute researchers fed healthy adults saccharin, sucralose, aspartame, or stevia and found that every one of them reshaped the community of bacteria in the gut, and that saccharin and sucralose measurably worsened people’s blood-sugar responses. That altered community is in constant chemical conversation with the brain along the gut-brain axis, the same signaling highway that ties your digestion to your mood and your appetite. Change who is living in the gut and you change the messages they send upstream. The sweetener never has to cross into your bloodstream to matter. It just has to change the tenants.
Erythritol is the one that genuinely unsettles me, because it does not stop at the gut. It shows up in the blood, and a 2023 Cleveland Clinic team reported in Nature Medicine that people with the highest circulating erythritol were about twice as likely to have a heart attack or stroke over the next three years, and that the compound appeared to make platelets easier to activate and quicker to clot. The brain is an organ that lives or dies on clean blood flow, so a sweetener that nudges the blood toward clotting is not a wild suspect. You do not need an exotic mechanism when the plumbing itself is under strain.
Here is what the study is and is not, in one breath. It is observational. It found links, not proof. People who drink a lot of diet soda differ from people who don’t in a hundred ways no questionnaire fully catches, and the diet data was self-reported, which is always a soft floor. Suemoto herself says plainly that more research is needed to confirm it, and that is the correct posture. Correlation is not proof. It is also not exoneration.
What I have no patience for is the reflex on the other side. When the results landed, the Calorie Control Council, the trade group that speaks for the sweetener industry, warned that the study “risks misleading the millions with diabetes.” Read that again. An industry group is telling diabetics not to worry about a signal that showed up most strongly in diabetics. That is not a neutral scientist counseling caution about correlation. That is the seller reassuring you about the product, and it is worth what such reassurances are usually worth.
And this is not a bolt from nowhere. A 2017 study in the journal Stroke found that people drinking at least one artificially sweetened beverage a day were roughly three times as likely to have an ischemic stroke and nearly three times as likely to develop Alzheimer’s dementia over the following decade. In 2023 the World Health Organization’s cancer agency classified aspartame as possibly carcinogenic to humans, a hazard flag the FDA promptly waved off. The pattern across all of it is the same. A class of additives sold for decades as the health-conscious default keeps accumulating signals that it is nothing of the kind, and the agencies and industry groups keep telling us the evidence isn’t good enough to act on. It never is, right up until it is.
The honest read is that we do not yet know whether these compounds are aging brains or merely riding along with something that is. But “we can’t prove it’s harmful” is a different sentence from “it’s safe,” and the burden here does not sit on the person asking the question. It sits on the people who put the swap in front of diabetics and called it responsible.
Me, I stopped waiting for certainty on this one. I would rather have real sugar in small, deliberate amounts, or nothing, than keep pouring a compound into midlife that six of seven times over tracked with a faster-aging brain. I do not need the guideline to change first. The diet can is already down.
Sources
- ScienceDaily – Popular sugar substitutes linked to faster brain aging (summary of the ELSA-Brasil analysis, July 2026)
- Neurology – Suemoto et al., Association Between Consumption of Low- and No-Calorie Artificial Sweeteners and Cognitive Decline
- American Academy of Neurology – press release with author comment and effect sizes
- Medical News Today – coverage including outside-expert critique and the Calorie Control Council response
- Cell – Suez et al. (2022), Personalized microbiome-driven effects of non-nutritive sweeteners on human glucose tolerance
- Nature Medicine – Witkowski et al. (2023), The artificial sweetener erythritol and cardiovascular event risk
- Stroke – Pase et al. (2017), Sugar- and Artificially Sweetened Beverages and the Risks of Incident Stroke and Dementia
- World Health Organization (2023) – Aspartame hazard and risk assessment results released