Roughly 2,100 dementia-free Australian adults who ate more ultra-processed foods scored worse on tests of attention and mental processing speed, even when the rest of their diet was relatively healthy. The findings, published in the journal Alzheimer’s and Dementia: Diagnosis, Assessment and Disease Monitoring, come from the Healthy Brain Project at Monash University, led by researcher Barbara Cardoso. The results add to a growing body of evidence from multiple countries suggesting that packaged snacks, sugary drinks, and other heavily processed items may quietly erode everyday cognitive sharpness well before any dementia diagnosis.
How a packet of chips a day tracks with slower thinking
The Monash University team used the NOVA food classification, a framework that sorts foods into four groups based on the degree of industrial processing they undergo. Participants reported their dietary intake, and researchers mapped those responses onto NOVA categories to estimate what share of each person’s diet came from ultra-processed products. Cognition was then measured through remote, unsupervised online tests validated for large-scale registries tracking people at risk for Alzheimer’s disease.
The central finding was direct: adults whose diets contained a higher proportion of ultra-processed foods performed measurably worse on attention and speed tasks. Cardoso framed the practical scale of the association by noting that a 10 percent increase in ultra-processed food intake is roughly equivalent to adding a packet of chips to a daily diet. That association held after the researchers adjusted for overall diet quality, meaning that eating plenty of fruits and vegetables did not fully offset the link between processed food and weaker cognitive performance.
The study’s testing method deserves attention on its own terms. The Healthy Brain Project relies on unsupervised online cognitive assessments, which participants complete at home rather than in a clinical setting. This approach allows researchers to recruit large samples quickly, but it also introduces variability. Distractions, device differences, and motivation can all influence scores in ways that a controlled lab environment would minimize. The project’s architects have published separate validation work showing the method can reliably capture attention and processing speed constructs at scale, but the tradeoff between reach and precision remains real.
Even with those caveats, the pattern within the Australian cohort was consistent. People who derived the largest share of their calories from ultra-processed foods tended to cluster at the lower end of performance on tasks that require rapid symbol matching or sustained focus. The differences were not so large that an individual would necessarily notice them in daily life, but on a population level they suggest a subtle drag on cognitive efficiency associated with heavily processed diets.
Parallel findings from U.S. cohorts strengthen the pattern
The Australian results do not stand alone. Data from the long-running Framingham Heart Study in the United States link daily servings of ultra-processed food to incident Alzheimer’s disease and broader dementia outcomes. That work uses a longitudinal design, following participants over years rather than capturing a single snapshot, which adds weight to the idea that dietary patterns and brain health are connected over time.
Separately, cross-sectional analysis of NHANES data from 2011 through 2014 tied higher ultra-processed food consumption to lower scores on the Digit Symbol Substitution Test, a well-established measure of processing speed and attention. And a nationally representative panel from the Health and Retirement Study examined ultra-processed food intake alongside impairment across multiple cognitive domains, including executive function, memory, and language, in older U.S. adults. Across these datasets, the same broad signal appears: people who eat more ultra-processed food tend to perform worse on tests that measure how quickly and accurately the brain handles information.
Researchers are cautious about over-interpreting these parallels. Each study uses slightly different dietary questionnaires, cognitive tests, and statistical adjustments. Yet the convergence across age groups and countries suggests the association is not a fluke of one particular dataset. Instead, it points toward a common thread linking industrially processed diets with a modest but measurable reduction in cognitive performance.
None of these studies, including the Healthy Brain Project analysis, can prove that ultra-processed foods cause cognitive decline. They are observational, meaning they identify associations but cannot rule out the possibility that people with declining cognition gravitate toward convenient, heavily processed meals for reasons unrelated to the food itself. Reverse causation and unmeasured confounders remain live concerns in every cohort, whether those confounders are socioeconomic status, sleep quality, depression, or other lifestyle factors that may influence both diet and brain function.
What a swap-one-snack trial could settle
The logical next question is whether changing what people eat can reverse or prevent the attention gaps these studies describe. One testable idea: adults who replace a single daily ultra-processed snack with a minimally processed alternative for six months should show measurable gains in processing speed on the same unsupervised tests the Healthy Brain Project uses, independent of any change in body weight. That kind of randomized trial would move the conversation from correlation to causation and would directly test whether the cognitive signal is driven by the food itself or by other lifestyle factors that travel alongside heavy ultra-processed food consumption.
No such trial has been published. The existing evidence base is built almost entirely on observational snapshots or longitudinal tracking without dietary intervention. The Healthy Brain Project’s cross-sectional design, in particular, cannot tell us whether the participants who scored lower on attention tests were already on a cognitive decline trajectory before their diets were measured, or whether their diets played any active role in that trajectory.
There are also gaps in the dietary data itself. The NOVA classification groups foods into broad categories, but the published analyses do not break out which specific ultra-processed items, whether soft drinks, packaged baked goods, or instant noodles, carry the strongest associations with cognitive outcomes. Without that granularity, dietary advice stays vague: “eat fewer ultra-processed foods” is hard to act on when the category spans everything from flavored yogurt to frozen pizza.
Practical takeaways amid uncertainty
For anyone paying attention to their own diet, the current science does not demand perfection or a complete purge of convenience foods. What it does support is a cautious, incremental approach: treating ultra-processed products as occasional extras rather than daily staples, and nudging the balance of the plate toward minimally processed items such as vegetables, whole grains, legumes, nuts, and plain dairy.
In practical terms, that might mean swapping a packet of chips for a handful of unsalted nuts a few days a week, choosing water or unsweetened tea over soft drinks, or keeping frozen vegetables and beans on hand as quick meal bases instead of relying on ready-made frozen dinners. These are small, feasible changes that align with broader cardiovascular and metabolic health goals, even as researchers continue to clarify how much they matter for thinking speed and attention.
The emerging evidence on ultra-processed foods and cognition should also be read alongside social and economic realities. Highly processed products are often cheaper, more heavily marketed, and more accessible than fresh alternatives, particularly in low-income neighborhoods. Any public health response that flows from this research will need to grapple with affordability and access, not just individual willpower.
For now, the signal is consistent enough to justify modest shifts in everyday eating, especially for middle-aged adults hoping to preserve cognitive function into later life. The Healthy Brain Project and U.S. cohorts cannot yet tell us whether those shifts will translate into fewer dementia diagnoses decades down the line. But they do suggest that what is in the snack aisle may be shaping how sharply many people think and focus today, long before memory problems rise to the level of a clinical concern.
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*This article was researched with the help of AI, with human editors creating the final content.
