Theoretical Frameworks for Understanding the Nutrition Transition in Sub-Saharan Africa: Evidence from a Multi-State Longitudinal Study in Nigeria

Existing theoretical frameworks for understanding nutrition transition, including Popkin's nutrition transition model and the food systems framework, were largely developed using data from high-income and rapidly industrialising Asian economies, limiting their applicability to the complex, heterogeneous trajectories observed in sub-Saharan African nations. This study develops and tests a contextualised theoretical framework for understanding the nutrition transition in Nigeria, drawing on longitudinal dietary, anthropometric, and socioeconomic data from a multi-state cohort study conducted in Lagos, Kano, Enugu, and Rivers States. A prospective mixed-methods longitudinal design tracked 2,400 households across four states over a three-year period with annual data collection waves. Quantitative instruments assessed household dietary diversity, ultra-processed food contribution to energy intake, anthropometric status of all household members, income and expenditure patterns, and food environment characteristics. Qualitative strands including ethnographic dietary observation and key informant interviews with food systems actors examined normative, cultural, and structural drivers of dietary change. Structural equation modelling with latent growth curve analysis examined between-state and within-state trajectories of nutrition transition indicators over time. A grounded theory approach informed by the qualitative data was used to generate a modified conceptual framework integrating food environment dynamics, cultural food identity, and informality in the Nigerian food system. Findings will challenge deterministic assumptions of nutrition transition theory and produce an original theoretical contribution to the global nutrition literature with particular relevance for heterogeneous developing-world contexts. Keywords: nutrition transition, theoretical framework, longitudinal study, Nigeria, food systems.