Many interventions aim to improve dietary patterns but not all are able to maintain these changes long term. Interventions informed by theory may facilitate dietary behavior changes and maintenance of these changes for longer periods of time. PubMed and PsychInfo were searched for theory-based interventions with long-term assessments of fruit and vegetable (FV) and fat intake. We identified 335 unique titles; 20 were included for review. Most interventions (65%) were based on social cognitive theory. Assessments of FV and fat ranged from 12 to 72 months postrandomization, and 15 studies reported significant intervention effects. Only 6 studies directly tested theory in relation to diet and of those, significant findings indicated self-efficacy, motivation for dietary change, perceived competence to eat more FV and less fat, and multiple processes of change were associated with long-term maintenance of healthy eating. Overall, this review indicates that theory-informed interventions are generally successful for long-term improvements in diet quality, although such improvements are often modest. Most studies did not directly measure theoretical constructs in relation to diet outcomes, thus limiting our ability to describe how theory-based interventions specifically promote long-term diet change. Recommendations for future research and practical recommendations for long-term maintenance of diet change are discussed.
Keywords: behavioral theory; diet quality; dietary fat; fruit and vegetable intake; maintenance.