Purpose: This study confirmed the effects of body mass index (BMI) and waist circumference (WC) on fasting blood glucose (FBS) and hemoglobin A1c (HbA1c) in adults without diabetes mellitus (DM). Methods: The subjects were 4,659 adults (≥20 years), and data were extracted from the 6th National Health and Nutrition Survey 2015 (KNHANES VI-3). The subject’s data were analyzed using a complex sample t-test, χ2-test, and multiple logistic regression analysis (SPSS 24.0). Results: The incidence of the high FBS group was increased 1.60 times in males with a WC ≥90 cm and 1.78 times in females with a WC ≥85 cm. The incidence of the high HbA1c group was increased 1.54 times in those who were overweight and 2.22 times in those who were obese. The incidence of the high HbA1c group was increased 1.99 times in males with a WC ≥90 cm and 1.87 times in females with a WC ≥85 cm. Conclusion: This study presented evidence that interventions for BMI and WC should be included in DM prevention programs. It also suggested that these findings can be utilized for early detection of DM.