Purpose: Theory-based approaches are now recommended to design and enact dietary interventions, but their use in cancer trials is unknown. This systematic review examined application of behavior theory to dietary interventions aimed at preventing cancer to improve the design and interpretation of trials.
Methods: Electronic databases were searched (inception-July 2011). Data were synthesized and a theory coding scheme (TCS) used to describe and assess how behavior theory informed interventions. Studies not reporting a dietary behavior intervention informed by a specified behavior change model(s) were excluded.
Results: Of 237 potentially eligible studies, only 40 (16.9 %) were relevant, mostly RCTs (34, 85.0 %). Twenty-one interventions targeted diet alone (52.5 %) or integrated diet into a lifestyle intervention (19, 47.5 %). Most (24, 60.0 %) invoked several behavior change models, but only 10 (25.0 %) interventions were reported as explicitly theory-informed and none comprehensively targeted or measured theoretical constructs or tested theoretical assumptions. The 10 theory-informed interventions were more effective at improving diet.
Conclusions: Dietary interventions for cancer prevention improved diet more effectively if they were informed by behavior theory. While behavior theory was often applied to these dietary interventions, they were rarely implemented or described thoroughly. Accurate intervention reporting is essential to assess theoretical quality and facilitate implementation effective behavior change techniques. Guidelines regarding the application and reporting of behavior theory for complex interventions, for example, proposed by the National Institutes of Health and Medical Research Council, should be revised accordingly. Failure to adequately ground dietary interventions in behavior theory may hinder establishing their effectiveness and relationships between diet and cancer.