BACKGROUND/OBJECTIVES: The Seoul Metabolic Syndrome Management (SMESY) program is a 1-yr lifestyle modification program targeting metabolic syndrome (MetS) in Seoul residents. This study investigated the associations between adherence to dietary guidelines and MetS among the SMESY program participants. SUBJECTS/METHODS: Data of 54,385 participants aged 20–64 yrs who completed the SMESY program in 2015, had information on adherence to dietary guidelines, and were not medicated for diabetes, hypertension, or dyslipidemia were analyzed. Participants underwent MetS screening and completed a lifestyle questionnaire including adherence to 10 dietary guidelines before and after participation. Participants were classified according to the number of MetS risk factors at baseline (MetS group, ≥ 3; risk group, 1–2; healthy group, none). Adherence to dietary guidelines was determined from the number of “yes” responses regarding the fulfillment of each guideline on ≥ 5 days/week. Multiple logistic regression was used to evaluate associations between newly diagnosed MetS and changes in adherence to dietary guidelines. RESULTS: In the MetS group, MetS prevalence decreased after the SMESY program (men, −41.9%p; women, −48.7%p), and all risk factors were significantly improved (P < 0.0001). All groups exhibited improved adherence to all dietary guidelines after participation (P < 0.0001). In the MetS group with positively changed adherence scores, the MetS prevalence decreased by −44.1%p for men and −49.5%p for women, whereas the prevalence in those with negative changes decreased by −38.1%p for men and −48.6%p for women. In the risk group, those with positively changed adherence scores had significantly decreased odds ratios (ORs) for newly diagnosed MetS compared with those with negative changes (OR, 0.70; 95% confidence interval [CI], 0.61–0.80 for men; OR, 0.88; 95% CI, 0.79–0.99 for women). CONCLUSIONS The SMESY program may effectively reduce the risk of MetS among adults with risk factors by improving adherence to dietary guidelines.