The Bitter Irony of “Sugar-Free”: When Artificial Sweeteners May Harm the Brain

For decades, low- and no-calorie sweeteners (LNCS) — the aspartames, saccharins, and sugar alcohols of the world — have been sold as the “smart swap” for sugar. They promised sweetness without calories, better blood sugar control, and, above all, a safer path for people with diabetes.

But a new 8-year prospective study published in Neurology (2025) tells a different story. Instead of protecting the brain, high consumption of LNCS was linked to faster cognitive decline — and the effect was strongest in people with diabetes, the very group most encouraged to use them.

What the Study Found

Researchers followed 12,772 Brazilian adults over 8 years, tracking their intake of seven common sweeteners (aspartame, saccharin, acesulfame K, erythritol, sorbitol, xylitol, and tagatose) and measuring changes in memory, verbal fluency, and overall cognition.

The results were striking:

• Higher sweetener intake = faster cognitive decline in memory, language, and global cognition.

• Daily users of LNCS experienced greater cognitive aging — the equivalent of losing an extra 1.3–1.6 years of brain function over the study period.

• Individual culprits: Aspartame, saccharin, acesulfame K, erythritol, sorbitol, and xylitol were all linked to faster decline. Tagatose was the exception — showing no harm, and even some protective effects in younger adults.

• Diabetes made things worse: Among participants with diabetes, LNCS use was strongly tied to faster decline across multiple cognitive domains.

Why Might This Happen?

The likely mechanism is brain insulin resistance.

• In diabetes, the brain already struggles to respond to insulin — a hormone that supports memory, learning, and energy balance.

• Artificial sweeteners can disrupt gut microbes, alter glucose signaling, and generate inflammatory metabolites that may further impair brain insulin signaling.

• In short: instead of helping, LNCS may amplify the very metabolic stress they were supposed to relieve.

The Bitter Irony

Here’s the paradox:

• LNCS were designed to protect diabetics from sugar-related harm.

• Yet, in this study, diabetics consuming LNCS suffered the fastest cognitive decline of all.

It’s a cruel twist — what’s marketed as “sugar-free and safe” may quietly accelerate memory loss and dementia risk in those who can least afford it.

What This Means for You

Does this mean everyone should toss out their diet soda tomorrow?

Not necessarily. This is one large observational study, and while it’s rigorous, it cannot prove cause and effect. But taken together with previous evidence linking LNCS to gut dysbiosis, glucose intolerance, and dementia, it raises red flags.

If you have diabetes, or if brain health is a concern, it may be worth rethinking your sweetener choices.

The Takeaway

Sweeteners were supposed to be the “solution.” Instead, they may be a silent contributor to the very problems they promised to solve — especially for people with diabetes. Sometimes, the bitter truth is that there really is no free sweetness.

Gonçalves, N. G., Figueiredo, R. C. de, Mota, B. C., Cardoso, L. O., Lotufo, P. A., Bensenor, I. M., & Schmidt, M. I. (2025). Association between consumption of low- and no-calorie artificial sweeteners and cognitive decline: An 8-year prospective study. Neurology, 104(3), e248–e260. https://doi.org/10.1212/WNL.0000000000219290

#Artificial sweeteners, #Cognitive decline, #Brain insulin resistance, #Diabetes, #Neuroinflammation