[Purpose] To compare the lifestyle habits of adults with and without suspicion of type 2 diabetes. [Methods] Participants were male and female adults aged 30 years or older who underwent the National Health Insurance health checkup in a city from 2008 to 2019. Included in the analysis were 10,401 participants who did not have missing data and were not actively improving their diet and lifestyles. Participants with suspected diabetes were defined as those with HbA1c (NGSP) ≥ 6.5% and/or those taking medication to lower blood glucose. The lifestyle habits of the two groups (whether diabetes was suspected or not) were compared by chi-squared test. Binomial logistic regression analysis adjusting for sex and age was then performed, in which suspected diabetes/others was the dependent variable and each lifestyle item was the independent variable. The analysis was conducted by age category (≥65 or <65 years of age). [Results] Among the participants <65 years of age, logistic regression analysis showed that significantly more participants with suspected diabetes did not engage in physical activity at least 1 hour a day, ate fast, and ate dinner within 2 hours before bedtime at least 3 times a week [Odds ratio (95% CI): 1.69 (1.22-2.32), 1.31 (1.01-1.72) and 1.52 (1.12-2.07), respectively]. However, significantly fewer participants with suspected diabetes drank 1 to 2 cups of alcohol per day [0.65 (0.46-0.92)]. Among the participants ≥65 years of age, significantly more participants with suspected diabetes did not engage in physical activity at least 1 hour a day, walked slower and ate faster than other persons of the same age [1.41 (1.18-1.70), 1.21 (1.01-1.45) and 1.29 (1.09-1.53), respectively]. [Conclusion] This study suggests that physical activity and not eating fast are important for the prevention of diabetes. Additionally, people <65 years of age should eat dinner within 2 hours before bedtime.