In the field of nutritional epidemiology, understanding the interplay between diet quality, specific food intakes, and the trajectories of cognitive and physical decline has become increasingly critical as populations age worldwide. Cognitive frailty, a dual syndrome of impaired cognition and physical frailty, is gaining recognition for its prognostic value with respect to disability, dependency, and mortality in older adults. Despite accumulating evidence that suggests dietary patterns and select food groups substantially influence both cognitive aging and frailty, significant gaps remain regarding how these dietary exposures shape longitudinal trajectories, the mechanisms at play, and cross-population applicability. Recent studies leverage prospective cohort designs, advanced dietary scoring systems, and the integration of omics and biomarker data, yet there is marked heterogeneity in dietary measurement, outcome assessment, and analytic approaches. As a result, comparability and synthesis across studies are hindered, and the translation of findings into intervention and policy remains limited.

This Research Topic aims to integrate and advance knowledge on how diet quality indices and specific foods contribute to the joint progression of cognitive and physical frailty, with an emphasis on longitudinal trajectories. The goal is to deepen understanding of causal pathways, refine methodological approaches, and clarify biological mechanisms linking nutrition and healthy aging. Furthermore, this topic seeks to stimulate research that supports the development of tailored interventions, harmonized data resources, and effective policies aimed at reducing age-related decline. Key questions include: Which dietary patterns or foods most robustly predict transitions in cognitive and frailty status? What are the best methodological practices for exposure and outcome assessment, trajectory modeling, and causal inference? How do biological and socio-environmental factors modify diet–cognitive-frailty links across diverse settings?

This Research Topic encompasses studies investigating the impact of diet and nutrition on cognitive-frailty trajectories, but excludes articles focused solely on single-timepoint associations or those unrelated to aging populations. To gather further insights in diet–cognitive-frailty relationships and their implementation in research and practice, we welcome articles addressing, but not limited to, the following themes:

o Harmonization of operational definitions and minimal datasets for cognitive frailty in nutritional epidemiology

o Comparative evaluation and application of diet quality indices and food group analyses in modeling trajectories of cognitive and physical decline

o Advanced methods for longitudinal and causal assessment, including trajectory modeling, compositional data analysis, and target trial emulation

o Biological mechanism-focused research leveraging omics, dietary biomarkers, and gut–muscle–brain pathways

o Exploration of life course, sociocultural, and environmental modifiers of diet–cognitive-frailty trajectories

o Design, implementation, and evaluation of nutritional interventions for cognitive-frailty prevention or mitigation

o Perspectives on global, cultural, and policy challenges in translating evidence to practice and guidelines

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Diet Quality, Specific Food Intakes, and Cognitive-Frailty Trajectories in Nutritional Epidemiology