Ultra-processed foods linked to lower memory and concentration in young adults

A new study published in Nutritional Neuroscience provides evidence that eating a diet high in ultra-processed foods tends to be associated with lower memory and concentration scores in young adults. The findings suggest that relying heavily on industrially processed snacks and meals might negatively affect cognitive performance during a period of life when the brain is still developing. These results highlight a potential link between modern dietary habits and mental function in early adulthood.

To understand these findings, it helps to look at how modern diets have shifted. Global food environments are increasingly dominated by ultra-processed foods. These are products created mostly from substances extracted from foods, like modified starches, hydrogenated fats, and protein isolates.

They often contain artificial additives like flavorings and preservatives while having very little whole-food content. Common examples include packaged baked goods, sugary drinks, ready-to-eat meals, and salty snacks. As people eat more of these products, scientists have proposed the idea of a neuro-nutritional transition.

This concept suggests that shifting away from natural foods toward heavily processed options might impact brain health as much as it impacts physical health. Previous research links heavy consumption of ultra-processed foods to negative cognitive outcomes in older adults. For example, older individuals eating a lot of these foods tend to show a higher risk of developing dementia and Alzheimer’s disease.

Despite this existing evidence in older populations, younger adults remain largely overlooked in nutritional research regarding brain health. Sara Rafiei, a nutrition researcher at the School of Public Health at the Iran University of Medical Sciences, and Mohammadreza Vafa, a professor of nutritional sciences at the same institution, wanted to address this knowledge gap.

“Ultra-processed foods have become a defining feature of modern diets, particularly among young adults,” the authors noted. “While their links with obesity, diabetes, cardiovascular disease, and even dementia have attracted growing attention, a fundamental question remained largely unanswered: could these foods be associated with cognitive performance long before the onset of age-related cognitive decline?”

They targeted young adulthood because it is a developmental stage where cognitive functions like memory and attention continue to mature. People in their late teens and twenties also report some of the highest intake levels of ultra-processed foods.

“This question is especially relevant because young adulthood is often considered the period of peak cognitive capacity, yet it is also a stage when ultra-processed food consumption reaches some of its highest levels,” the authors explained. “We wanted to investigate whether dietary habits traditionally viewed through the lens of physical health might also be associated with everyday cognitive functions, such as memory and concentration.”

“We believe one of the most important aspects of our findings is that they shift the conversation about ultra-processed foods beyond chronic disease and aging,” Rafiei and Vafa added. “Much of the existing research has focused on dementia and cognitive decline later in life. Our study suggests that associations between ultra-processed food consumption and cognitive performance may already be detectable in young adulthood, a period traditionally viewed as neurologically robust.”

“If confirmed by future research, this would imply that the cognitive consequences of dietary patterns may begin much earlier than previously assumed,” they said. “In other words, the foods we choose today may be relevant not only to how we age, but also to how effectively we think, learn, and remember right now.”

The mechanisms by which these foods might compromise brain function are complex. Diets high in ultra-processed foods are typically rich in refined sugars, saturated fats, and sodium, while lacking essential micronutrients required for brain health. These foods are also engineered to be hyper-palatable through the use of cosmetic additives and emulsifiers.

These specific additives can alter the composition of gut bacteria. Changes in the gut microbiome can disrupt the signaling pathways that communicate with the brain, often referred to as the gut-brain axis. Such dietary patterns are also associated with systemic inflammation and insulin resistance, which can impair the brain’s ability to adapt and form new memories.

To explore this topic, the researchers conducted a cross-sectional study. A cross-sectional study is a type of observational research that analyzes data from a population at one specific point in time. The scientists recruited 416 university students between the ages of 18 and 35. The average age of the participants was just over 22 years old.

To measure what the participants ate, the researchers used a dietary assessment method called a 24-hour recall. A trained nutritionist interviewed each participant on two separate, non-consecutive days to record everything they ate and drank during the previous 24 hours. Using specialized software and local food databases, the scientists calculated the total energy and nutrient intake for each student.

Next, the researchers classified all reported foods using the NOVA system. The NOVA system is a widely used framework that groups foods based on the extent and purpose of their industrial processing. They specifically calculated the percentage of each participant’s total daily calories that came from ultra-processed foods. On average, ultra-processed foods accounted for 29.5 percent of the participants’ total daily energy intake.

To evaluate cognitive performance, the researchers administered two standardized tests. They assessed mental concentration using the Toulouse-Pieron Test, a widely used measure of sustained attention. This test requires the participant to quickly and accurately scan and identify specific visual patterns within a three-minute time limit. The total score represents the individual’s attentional efficiency, factoring in correct marks and penalizing missed ones.

Short-term memory was tested using the Numerical Learning Test, which assesses sequential memory. In this task, participants listened to a series of nine-digit numbers read aloud, one digit per second, and had to recall them in the exact order they were presented. The sequence was repeated multiple times to see how well the person progressively memorized the series.

The researchers used statistical models to look for associations between the proportion of ultra-processed foods in the diet and the scores on these cognitive tests. They adjusted their models to account for several other factors that might influence brain function. These adjusted factors included the participants’ sex, caffeine intake, use of dietary supplements, physical activity levels, sleep duration, and smoking status.

They also accounted for psychological distress, measuring depression, anxiety, and stress levels through a standardized questionnaire. The results showed a negative association between the consumption of ultra-processed foods and short-term memory. The researchers found that for every 10 percent increase in the proportion of daily calories coming from ultra-processed foods, short-term memory scores dropped by 0.54 points.

This association remained statistically significant even after adjusting for all the lifestyle and psychological factors. “What surprised us most was the consistency of the association with memory,” the authors said.

“Even after accounting for psychological distress, sleep duration, physical activity, caffeine intake, smoking, and supplement use, the relationship between ultra-processed food intake and memory remained remarkably stable,” they noted. “This suggests that the observed association was not simply explained by these commonly cited lifestyle factors.”

The scientists also divided the participants into three equal groups based on their intake of ultra-processed foods. These groups are known as tertiles. Participants in the highest tertile, meaning they ate the most ultra-processed foods, had an adjusted average memory score of 17.59. In comparison, those in the lowest tertile scored an average of 19.60.

For mental concentration, the associations were weaker but still present. The researchers found that each 10 percent increase in ultra-processed food intake was associated with a 0.138-point decrease in the concentration score. However, when comparing the highest consuming group to the lowest consuming group, the differences in concentration scores lost their statistical significance after adjusting for all lifestyle factors.

“We were also intrigued by the possibility that different cognitive domains may not be equally sensitive to dietary exposures,” the authors explained. “Memory appeared to be more strongly associated with ultra-processed food intake than with concentration, which raises interesting questions about the underlying neurobiological mechanisms.”

The authors suggest that attentional networks in the prefrontal cortex might be more influenced by short-term environmental factors like immediate stress or caffeine. This makes the dietary link harder to observe. Memory networks in the brain, particularly those involving the hippocampus, might be especially vulnerable to diet-induced inflammation and oxidative stress.

To look for specific consumption patterns, the researchers used an advanced statistical technique that allows scientists to see if a relationship changes at different points, rather than assuming a straight, continuous line. This analysis revealed a specific threshold effect for memory. Memory scores remained relatively stable when ultra-processed foods made up less than 20 percent of a person’s daily diet.

Once consumption crossed that 20 percent mark, memory scores tended to drop more sharply. This pattern suggests that the brain might tolerate small amounts of these foods but struggles when they make up a larger portion of the diet.

“The observed effects were modest at the individual level, which is typical in population-based nutrition research where cognition is influenced by many interacting factors,” Rafiei and Vafa said. “However, small effects can have substantial public health implications when the exposure is widespread. Ultra-processed foods now contribute a large proportion of total energy intake in many populations worldwide.”

“Even modest cognitive differences associated with such a common dietary exposure could translate into meaningful effects at the population level,” they continued. “Interestingly, our dose-response analyses suggested that memory performance remained relatively stable at lower levels of ultra-processed food consumption but began to decline more noticeably once intake exceeded approximately 20% of daily energy intake. While this should not be interpreted as a strict threshold, it suggests that higher levels of exposure may be particularly relevant.”

As a final check, the researchers performed a sensitivity analysis by removing participants who reported severe or extremely severe psychological distress. This step helped isolate the effects of diet from the effects of severe mental health struggles.

Following this exclusion, the inverse association between ultra-processed food intake and short-term memory remained nearly identical. Interestingly, the negative association between diet and mental concentration actually became stronger after excluding these highly distressed participants.

Overall, the study provides evidence that relying on highly processed meals is linked to poorer mental function.

“The key message is that diet may matter not only for your future health but also for how your brain functions today,” the authors explained. “In our study, young adults who consumed more ultra-processed foods tended to perform worse on measures of short-term memory and, to a lesser extent, on measures of concentration.”

“Although our findings do not prove cause and effect, they add to a growing body of evidence suggesting that dietary choices may influence cognitive performance even during the years when people generally consider themselves cognitively resilient,” they said. “For students, professionals, and anyone who relies on learning, memory, and sustained mental performance, this perspective is important. Nutrition may be part of the conversation not only about preventing disease decades later, but also about optimizing cognitive function in the present.”

While these findings provide evidence linking diet to cognitive performance, there are potential misinterpretations to avoid. Because this was a cross-sectional study, it only provides a snapshot in time.

“The most important point is that this was a cross-sectional study,” Rafiei and Vafa cautioned. “Therefore, we cannot conclude that ultra-processed foods directly cause poorer memory or concentration. The relationship may operate in both directions.”

“For example, individuals with certain behavioral or cognitive characteristics may be more likely to consume ultra-processed foods,” they noted. “Longitudinal and intervention studies are needed before causal conclusions can be drawn. Another important point is that our findings should not be interpreted as evidence that occasional consumption of ultra-processed foods is harmful. Rather, the study focuses on overall dietary patterns and habitual intake over time.”

There are several other limitations to consider. The study relied on participants accurately remembering and reporting their food intake, which can sometimes lead to measurement errors. The study also did not use broader diet quality indices, making it difficult to completely separate the specific effects of industrial processing from generally poor nutritional habits.

The sample consisted entirely of students from a single medical university in Iran. This specific group might have higher baseline cognitive performance and health awareness than the general public. As a result, the findings might not easily apply to young adults from different educational, cultural, or socioeconomic backgrounds.

The scientists intentionally excluded body mass index and metabolic markers from their statistical adjustments. They reasoned that metabolic changes might act as intermediate steps in the biological pathway between eating highly processed foods and experiencing cognitive changes. Adjusting for them might artificially hide the true effect of the diet.

Future research could address these limitations by observing individuals over a long period of time.

“One of the most important next steps is determining whether these associations are causal and potentially reversible,” the authors said. “We are interested in prospective studies that follow young adults over time, as well as dietary intervention trials that examine whether replacing ultra-processed foods with minimally processed alternatives leads to measurable improvements in cognitive performance.”

“We are also interested in understanding the biological pathways involved,” they added. “Emerging evidence points toward mechanisms involving systemic inflammation, metabolic dysfunction, and alterations in the gut-brain axis. Future studies integrating biomarkers, neuroimaging, and dietary interventions could provide valuable insight into how dietary processing influences brain health.”

The study, “Ultra-processed food consumption and cognitive performance in young adults: associations with mental concentration and memory,” was authored by Sara Rafiei, Maryam Nohegari, Parvin Sarbakhsh, and Mohammadreza Vafa.