Do implementation intentions help to eat a healthy diet? A systematic review and meta-analysis of the empirical evidence

Objective: This systematic review and meta-analysis examined whether implementation intentions are an effective tool to help people put their intentions to eat a healthy diet into practice. Additionally, it was investigated whether the quality of the outcome measures and the quality of the control conditions that are used in these studies influence implementation intentions' effectiveness. Methods: Twenty three empirical studies investigating the effect of implementation intentions on eating behavior were included. In assessing the empirical evidence, a distinction was made between studies that aim to increase healthy eating (i.e., eating more fruits) and studies that aim to diminish unhealthy eating (i.e., eating fewer unhealthy snacks). Results: Implementation intentions are an effective tool for promoting the inclusion of healthy food items in one's diet (Cohen's d = .51), but results for diminishing unhealthy eating patterns are less strong (Cohen's d = .29). For studies aiming to increase healthy eating, it was found that higher quality outcome measures and lower quality control conditions tended to yield stronger effects. Conclusion: Implementation intentions are somewhat more effective in promoting healthy eating than in diminishing unhealthy eating, although for some studies promoting healthy eating effect sizes may have been inflated due to less than optimal control conditions.