More unprocessed food, lower dementia odds in older Iranian adults, study finds

Older adults who ate more unprocessed foods had markedly lower odds of major neurocognitive disorder, according to a cross-sectional analysis drawn from the second phase of the Birjand Longitudinal Aging Study, conducted in Iran between November 2021 and May 2022. Among the 1,017 participants, who had a mean age of 72.4 years and of whom 50.2% were female, 13.8% met criteria for major neurocognitive disorder. In the study’s principal analytical model, higher unprocessed food intake was associated with 45% lower odds of the condition, with an odds ratio of 0.55 and a 95% confidence interval of 0.32 to 0.92.

The research team assessed dietary intake with a validated semi-quantitative food frequency questionnaire and classified foods according to the NOVA system, which groups items by the extent and purpose of industrial processing rather than by nutrient content alone. Ultra-processed foods, in this framework, are industrially formulated products containing various additives. Cognitive status was not self-reported: a neurologist determined each diagnosis using DSM-5 criteria, neuropsychological testing, structured interviews and, when clinically indicated, magnetic resonance imaging. Logistic regression models were then used to estimate the association between each processing category and the odds of disorder.

The pattern of results was not uniform across processing levels. Participants with major neurocognitive disorder were more often female, had lower educational attainment and consumed fewer unprocessed foods than those without the diagnosis. While higher unprocessed food intake was consistently associated with lower odds of the disorder across sequential statistical models, the analysis found no statistically conclusive evidence of an association between intake of processed foods or ultra-processed foods and the condition. The authors therefore describe the ultra-processed food findings as inconclusive rather than reassuring or damning.

Several limitations temper the interpretation. Because the study is cross-sectional, it captures diet and cognitive status at a single point in time and cannot establish that eating patterns caused differences in brain health; reverse causation remains possible, since cognitive decline can itself alter food choices and preparation habits. The researchers also note that the NOVA classification does not fully capture overall dietary quality, meaning the processing categories may obscure the role of nutrient composition. They call for longitudinal research to disentangle the relationships between food processing, nutrient content and cognitive health over time.

Still, the association reported here is an observational one from a single phase of a regional aging study, and the confidence interval around the central estimate, while excluding the null value in the principal model, reflects uncertainty that future longitudinal phases of the Birjand study and similar cohorts elsewhere will need to address before any dietary guidance can be drawn from processing level alone.

Subject of Research: The association between unprocessed and ultra-processed food intake and major neurocognitive disorder in older adults

Article Title: Unprocessed vs. ultra-processed food intake and major neurocognitive disorder (MNCD) among older adults: insights from the second phase of the Birjand longitudinal aging study

Article References: Pak, A., Ramezani, A., Moodi, M., Khodabakhshi, H., Monji, H., Fakhrzadeh, H., Ejtahed, H.-S., & Sharifi, F. (2026). Unprocessed vs. ultra-processed food intake and major neurocognitive disorder (MNCD) among older adults: insights from the second phase of the Birjand longitudinal aging study. Aging Clinical and Experimental Research. https://doi.org/10.1007/s40520-026-03548-4

Image Credits: AI Generated

DOI: 10.1007/s40520-026-03548-4

Keywords: ultra-processed foods, unprocessed foods, NOVA classification, major neurocognitive disorder, dementia, older adults, cross-sectional study, Birjand Longitudinal Aging Study, diet and cognition, food frequency questionnaire, Iran, logistic regression