BACKGROUND/OBJECTIVES: Abdominal obesity is associated with metabolic disorders, and, in recent years, its prevalence in Korea has continuously increased. The change of lifestyle, particularly diet, is critical for the reduction of abdominal obesity. This study evaluated the effectiveness of an intervention focused on dietary self-efficacy and behaviors on the improvement of abdominal obesity. SUBJECTS/METHODS: Abdominally obese adults with additional cardiovascular risk factors were recruited through 16 medical facilities in South Korea from the year 2013 to 2014. The participants were randomly divided into 2 groups: an intensive intervention group (IG) that received a multi-component intervention to reduce abdominal obesity, by mainly focusing on dietary attitude and dietary behavior change, and a minimal information intervention group (MG) that received a brief explanation of health status and a simple recommendation for a lifestyle change. The interventions were provided for 6 mon, and health examinations were conducted at baseline, 3-, 6-, and 12-mon follow-ups. A path analysis was conducted to identify the process governing the changes in abdominal obesity. RESULTS: The IG showed an improvement in self-efficacy for eating control and diet quality at 6-mon follow-up. Abdominal obesity improved in both groups. Waist circumference was observed to be decreased through the path of “improved self-efficacy for eating control in food availability—eating restriction—improved dietary quality” in IG. Most changes in follow-ups were not significantly different between two groups. CONCLUSIONS The intensive program targeting the modification of dietary behavior influenced management of abdominal obesity, and the effect occurred through a step-by-step process of change in attitude and behavior. Generally, improvements were also seen in the MG, which supports the necessity of regular health check-ups and brief consultation. The results can be used for further development and implementation of more successful interventions.Trial Registration: Clinical Research Information Service Identifier: KCT0000762