Why do some local food availability interventions fail to modify diet quality? A realist review and synthesis and proposed systemic theory of change

Background: Despite promising observational evidence, evaluations of interventions and policies to improve local food availability, diet and obesity report a lack of effectiveness. Often implemented without an explicit theory of change, understanding failure is limited. This study aimed to develop a theory of change (ToC) and map existing local food availability evaluation related literature.

Methods: An expert panel participated in a concept mapping and consensus workshop to develop an initial ToC. A systematic search of evaluation literature and synthesis guided by the Realist And Meta-narrative Evidence Syntheses publication standards was done. Content from evaluation literature was mapped onto the ToC based on identified context, mechanism, and outcome (CMO) configurations to determine tested and hypothesized pathways.

Results: The workshop resulted in a realist informed ToC that made explicit the ‘system’ in which food availability interventions are implemented. A process of sequential interactions across both space and time was articulate. The ToC included long causal chains across multiple levels of context converging on several theorised mechanisms to explain food choice and dietary patterns.

Conclusions: The resulting ToC suggests that reductionist approaches to local food availability interventions may result in limited generalisable insights between varying contexts, possible unintended consequences or incomplete conclusions.