Dietary diversity indicators: evolution, measurement, and interpretative challenges

Dietary diversity is widely used to assess food variety and household food access, and as a proxy for nutrient adequacy; however, substantial heterogeneity in indicator construction and interpretation limits comparability across studies. This narrative-conceptual review examined the evolution, measurement, and application of dietary diversity indicators, drawing on literature identified through Scopus, Web of Science, PubMed, reference screening, and relevant institutional guidance. The synthesis distinguished six overlapping methodological categories: food-count-based, composite and dietary guideline-based, nutritional, sustainability- and biodiversity-oriented, temporal, and personalised or biological approaches. Evidence shows that dietary diversity has evolved from simple counts of foods or food groups to multidimensional assessments that incorporate richness, evenness, dissimilarity, nutritional value, species diversity, temporal variability, and individual biological responses. However, indicators within these categories measure distinct constructs and operate at different analytical scales. Accordingly, higher diversity cannot be interpreted universally as evidence of nutrient adequacy, diet quality, health, or environmental sustainability. Household food access, individual consumption, and national food availability likewise require context-based interpretation. The review demonstrates that indicator validity depends less on methodological complexity than on alignment among the construct measured, the unit of analysis, the intended application, and the outcome evaluated. Greater harmonisation of food classifications, reference periods, scoring procedures, and reporting standards is needed. This review advances dietary diversity work by establishing a foundation for matching indicators to specific research and policy objectives and for interpreting findings with greater conceptual and methodological precision.