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Accurately capturing what people eat and drink remains one of the greatest challenges in public health nutrition and nutrition epidemiology. Despite decades of refinement, self-report tools, such as food frequency questionnaires, diet diaries, and recalls remain prone to recall bias, under-or over-reporting, and cultural variability. These limitations introduce systematic error into diet, disease relationships, complicating causal inference and undermining reproducibility.The first volume of this Research Topic underscored the importance of developing and validating objective dietary assessment methods, including the use of biomarkers, digital technologies, and calibration models. Volume II builds on this momentum, bringing together 21 original contributions spanning multiple continents, dietary cultures, and methodologies. Collectively, these studies illustrate the richness of approaches being pursued: novel dietary indices, validation of culturally tailored tools, population-level surveillance, and integration of nutritional biomarkers with epidemiological outcomes.A core theme in this volume is the use of dietary indices to capture overall diet quality or nutrientspecific exposures in relation to chronic disease outcomes.Yu et al. assessed diet quality and quantity using the Chinese Diet Balance Index 2022, demonstrating that imbalances in diet quality increased the risk of sarcopenia. Their findings highlight the relevance of multidimensional diet quality indices in ageing populations.Wen et al. investigated the Composite Dietary Antioxidant Index (CDAI) in relation to growth indicators among children aged 3-12 years, showing that antioxidant-rich diets were associated with more favourable growth trajectories. Complementing this, Cheng et al. applied the CDAI to a U.S. paediatric population, revealing associations between antioxidant intake and susceptibility to Epstein-Barr virus infection, thus extending the relevance of CDAI beyond growth into infectious disease risk.Zhou et al. explored the Oxidative Balance Score (OBS) and found significant associations with peripheral artery disease in U.S. adults, underscoring the role of diet-driven oxidative stress in vascular health. Yang et al. added to this theme by reporting that higher dietary phosphorus intake was protective against cardiovascular mortality among individuals with asthma, illustrating how nutrient-specific measures can be applied to at-risk clinical populations.Altogether, these studies demonstrate the power of composite indices and targeted nutrient measures as standardised approaches to link diet with a spectrum of chronic health outcomes.A second cluster of papers examined dietary diversity, nutrient intake, and diet-related risks across diverse populations. These analyses provide a picture of dietary diversity and risk factors across Asia, the Middle East, and Africa, illustrating the geographic breadth of challenges in dietary assessment and the need for culturally sensitive, region-specific dietary surveillance.Advances in dietary assessment methodology were another major theme of this collection.Saxby et al. piloted the feasibility of self-reported dietary recalls among newly diagnosed multiple sclerosis patients, demonstrating that dietary recalls remain practical, though they require adaptation to clinical contexts. Ni et al. developed and validated a food frequency questionnaire tailored for pregnant women from the Chinese Miao ethnic group, demonstrating both reproducibility and validity in a culturally specific population, a critical step towards equitable dietary research.Ahern et al. analysed secular trends in ad libitum energy intake in controlled research settings from 1999 to 2020, showing both consistency and shifts that underscore the importance of methodological calibration across decades of study designs.Wardenaar and colleagues contributed two related studies in sports nutrition: first, the development of the Safe Supplement Screener (S3), designed to assess risk behaviour in supplement use among athletes; and second, a cross-validation study of S3 in NCAA Division I athletes. Together, these papers highlight how structured, evidence-based screeners can enhance accuracy and safety in supplement reporting, where misclassification may have clinical and regulatory implications.These methodological contributions collectively underscore the importance of ongoing validation, cultural tailoring, and integration of new tools into specific research and clinical populations.Several contributions addressed dietary assessment in vulnerable or clinical populations where nutritional risks are acute. These papers reinforce the crucial role of accurate, context-appropriate dietary assessment in vulnerable groups, where the stakes for mismeasurement are particularly high.The 21 contributions in Volume II collectively extend the field of dietary assessment in three critical ways. First, they demonstrate the expanding toolkit of indices, screeners, and validated questionnaires capable of capturing both nutrient-specific and overall dietary exposures. Second, they highlight the importance of context and population diversity, with studies spanning children, pregnant women, athletes, elderly populations, and patients with chronic or infectious diseases, across Asia, Africa and the Middle East. Finally, they highlight the integration of objective and semi-objective approaches, from biomarkers and antioxidant indices to digital tools and culturally specific FFQs as the path forward for more reliable nutritional epidemiology.As dietary assessment continues to evolve, the integration of objective tools with culturally sensitive approaches will be essential for advancing global nutrition science.Persistent challenges remain. These include the need to:• Harmonise methods across cohorts to enable comparability.• Reduce cost and participant burden to scale objective methods.• Integrate self-report and objective measures through robust calibration.• Ensure cultural adaptability and equity in dietary assessment tools.The contributions in this volume demonstrate that the field is moving rapidly toward more precise, inclusive, and technologically enabled dietary assessment. By building on methodological innovation and global diversity, the work presented here brings us closer to resolving the long-standing limitations of dietary self-report and strengthening the evidence base for diet, disease relationships.We thank all authors, reviewers, and the editorial team for their efforts, and we hope this collection helps future innovation and collaboration, creating more accurate, equitable, and globally relevant dietary epidemiology.