We investigated the association between fast-food (FF) consumptions and the risk of overweight/obesity and dyslipidemia in Korean adults (20–39 years) based on the Korea National Health and Nutrition Examination Survey (2013–2014). We also examined the effect of breakfast intake on the risk of overweight/obesity and dyslipidemia according to their frequencies of FF consumption. FF consumption was categorized into 3 groups: < 1 time/month (n = 79); 1–3 times/month (n = 1,173); and ≥ 1 time/week (n = 474). People consuming FF ≥ 1 time/week had unhealthy lifestyles, higher intake of total calorie, fat, and protein, and higher levels of blood pressure, total cholesterol (TC) and low-density lipoprotein (LDL)-cholesterol than those consuming FF < 1 time/month. Logistic regression analysis showed higher risk of overweight/obesity in people consuming FF 1–3 times/month (odds ratio [OR], 2.525; confidence intervals [CIs], 1.169–5.452; p = 0.018) and ≥ 1 time/week (OR, 2.646; CIs, 1.128–6.208; p = 0.025) than those consuming FF < 1 time/month after the adjustment. The risk of dyslipidemia was also higher in people consuming FF ≥ 1 time/week than those consuming FF < 1 time/month after the adjustment (OR, 2.444; CIs, 1.047–5.704; p = 0.039). Furthermore, among people consuming FF ≥ 1 time/week, irregular breakfast consumers (≤ 2 times/week, n = 215) had significantly higher levels of triglyceride, TC, and LDL-C than regular breakfast consumers (5–6 times/week, n=180). Irregular breakfast consumers also showed a higher risk of dyslipidemia than regular breakfast consumers after the adjustment (OR, 2.913; CIs, 1.463–5.801; p = 0.002). In conclusion, frequent FF consumption increases the risk of obesity and dyslipidemia in Korean adults aged 20–39 years. Particularly amongthe frequent FF consumers, irregular breakfast intake may contribute to the increased risk of dyslipidemia. It may provide an evidence for proper dietary education to reduce the risk of overweight/obesity and dyslipidemia in Koreans adults aged 20–39 years.