Junk Food Is Already Hurting Young Adults’ Memory, Not Just Their Future Health

Most warnings about ultra-processed food and the brain point decades into the future, toward dementia and cognitive decline in old age. A new study published in Nutritional Neuroscience suggests the damage may already be showing up in people in their twenties. Researchers at Iran University of Medical Sciences found that university students who ate more ultra-processed foods scored measurably lower on tests of short-term memory, and to a lesser extent, mental concentration.

Ultra-Processed Food Consumption Predicts Lower Short-Term Memory Scores

The study's core numbers are straightforward. For every 10% increase in the share of daily calories coming from ultra-processed foods, short-term memory scores fell by 0.54 points on a standardized test. Participants in the highest tier of UPF consumption averaged a memory score of 17.59, compared to 19.60 for those in the lowest tier. That gap held up after the researchers adjusted for sex, caffeine intake, physical activity, sleep duration, smoking, and psychological distress.

The concentration finding was more fragile. Each 10% rise in UPF intake was associated with a 0.138-point drop in concentration scores, but that association lost statistical significance once all lifestyle and psychological variables were controlled. A sensitivity analysis that excluded participants with severe psychological distress told a more interesting story: the memory association held firm, and the concentration association actually strengthened. Stress and anxiety, in other words, were masking part of the signal.

One threshold stood out. Memory scores stayed relatively stable when UPFs made up less than 20% of the daily diet, then dropped more sharply once consumption crossed that mark. On average, UPFs accounted for 29.5% of participants' total daily energy intake, meaning most of the sample was already above the apparent threshold.

Research reviewed by the NIH and others has documented UPFs and neurocognitive harm across the lifespan, including executive-function deficits and reward-circuit disruption extending to dementia. This study adds evidence that the pattern begins far earlier than most people assume.

Why Cognitive Effects in Young Adults Carry Public Health Weight

Young adulthood is not a neurologically static period. Cognitive functions, particularly working memory and executive control, continue maturing into the mid-twenties. That makes it a window of vulnerability, not immunity, and one where dietary habits tend to be worst.

Sara Rafiei and Mohammadreza Vafa, the study's lead researchers, framed the significance this way: "The key message is that diet may matter not only for your future health but also for how your brain functions today. 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."

The individual-level effects are modest. But as Rafiei and Vafa note, modest effects multiplied across populations where UPF intake is near-universal produce substantial public health consequences. A University of Michigan summary of Lancet meta-analyses found high UPF diets associated with increased risk for 12 conditions, including depressive symptoms and type 2 diabetes. Cognitive performance in young adults is now a credible addition to that list.

Separate research from Monash University found that even slight daily increases in ultra-processed food intake were linked to lower scores on standardized tests of visual attention and processing speed, corroborating the direction of the Iranian findings in a different population.

How the Study Measured Diet and Cognition in 416 Students

The researchers recruited 416 university students aged 18 to 35, with an average age of around 22, from one medical university in Iran. Dietary intake was measured through two non-consecutive 24-hour dietary recalls, conducted by a trained nutritionist. Foods were classified using the NOVA system, which groups products by the degree and purpose of processing rather than by nutrient content. Ultra-processed foods under NOVA are products made primarily from food-extracted substances, such as modified starches, hydrogenated fats, and protein isolates, combined with artificial additives and minimal whole-food content. Packaged baked goods, sugary drinks, ready-to-eat meals, and salty snacks are typical examples.

Short-term memory was assessed with the Numerical Learning Test; concentration was assessed with the Toulouse-Pieron Test. Statistical models adjusted for the usual confounders. Notably, the researchers deliberately excluded BMI and metabolic markers from their adjustments, reasoning that these might be intermediate steps in the causal chain rather than independent controls.

Cross-Sectional Design Limits Causal Claims, and Other Open Questions

The study's authors are candid about what their design cannot establish. "The most important point is that this was a cross-sectional study. Therefore, we cannot conclude that ultra-processed foods directly cause poorer memory or concentration. The relationship may operate in both directions," Rafiei and Vafa wrote. Students who already struggle cognitively might make worse food choices; the data cannot rule that out.

Self-reported dietary recall also introduces measurement error, and the sample, drawn from a single medical university in Iran, may not generalize to other cultural or demographic groups. The study also did not use broader diet quality indices, so it is difficult to fully separate the effects of food processing itself from the general nutritional poverty of UPF-heavy diets.

Those methodological challenges are not unique to this team. Nutritional epidemiology research on ultra-processed foods consistently struggles to disentangle whether harm comes from processing, from low nutrient density, or from correlated lifestyle factors. Longitudinal studies with objective dietary biomarkers are needed to resolve the causal question.

What Could Reduce UPF Intake Among Young Adults

The study's proposed mechanisms run through several biological pathways. Diets heavy in refined sugars, saturated fats, and sodium while low in essential micronutrients are associated with systemic inflammation and insulin resistance, both of which impair brain adaptability and memory formation. Emulsifiers and cosmetic additives in UPFs can also alter gut bacteria composition, disrupting the gut-brain axis in ways that may affect cognition independently of calories.

Rafiei and Vafa call for longitudinal research that tracks young adults over time, ideally using biomarkers rather than self-report. On the intervention side, the NIH has outlined multi-level strategies to reduce UPF consumption, including front-of-package labeling, school meal standards, and marketing restrictions. Given that cognitive effects appear detectable before chronic disease develops, the case for intervening early in the life course has grown stronger.

Evidence rating

EMERGING — 71/100

Caveats:

• Cross-sectional design only — the study captures a single point in time, so it cannot establish that ultra-processed foods cause poorer memory; reverse causation (e.g., people with lower cognitive engagement choosing less nutritious diets) cannot be ruled out.
• Sample was entirely drawn from one medical university in Iran; students likely have higher baseline health awareness than the general young-adult population, limiting how broadly the findings apply.
• Dietary intake was measured by self-reported 24-hour recall on two days, which is subject to memory errors and may not reflect habitual long-term diet.
• Funding source was not disclosed in the available reporting; independent replication has not yet occurred.

Cross-sectional observational study of 416 university students (mean age ~22) in Iran. Reports a statistically significant inverse association between ultra-processed food intake and short-term memory scores after adjustment for lifestyle and psychological confounders; the concentration finding was weaker and lost significance after full adjustment. Because the design captures one point in time, it demonstrates association only and cannot establish causation or rule out reverse causation. The sample is limited to students at a single institution, and findings have not been independently replicated.

References

1. Sara Rafiei, Maryam Nohegari, Parvin Sarbakhsh, Mohammadreza Vafa (2026). Ultra-processed food consumption and cognitive performance in young adults: associations with mental concentration and memory. Nutritional Neuroscience. https://doi.org/10.1080/1028415x.2026.2674151
2. Gaia Mottis, Pratheba Kandasamey, Daria Peleg-Raibstein (2025). The consequences of ultra-processed foods on brain development during prenatal, adolescent and adult stages. Frontiers in Public Health. https://doi.org/10.3389/fpubh.2025.1590083
3. New studies say ultraprocessed foods seen as global public health threat. news.umich.edu. https://news.umich.edu/new-studies-say-ultraprocessed-foods-seen-as-global-public-health-threat/
4. Ultra-processed foods damage your focus even if you eat healthy – Monash University. monash.edu. https://www.monash.edu/news/articles/ultra-processed-foods-damage-your-focus-even-if-you-eat-healthy
5. Svetlana V. Doubova, Claudio Quinzaños Fresnedo, Martín Paredes Cruz, et al. (2024). A comprehensive assessment of care competence and maternal experience of first antenatal care visits in Mexico: Insights from the baseline survey of an observational cohort study. PLOS Medicine. https://doi.org/10.1371/journal.pmed.1004456
6. Ultra-Processed Food: Investigating Mechanisms, Prevention, and Action for Chronic Disease and Health Transformation (UPF-IMPACT). NIH. https://dpcpsi.nih.gov/sites/default/files/docs/2026_05_11_Ultra-Processed_Food_Concept.pdf