ObjectiveThe aim of this study was to evaluate the change in fasting blood sugar (FBS) over time and its determinants in diabetic patients. MethodsA longitudinal data analysis retrospective-based study was considered with a sample of 312 patients, and the linear mixed effect model was applied. ResultsBased on the linear mixed model, the 3-month change in time decreases the average FBS level by 0.0111. An increase of one unit of body mass index (BMI) increases the FBS level by 0.0434. Similarly, an increase in blood pressure (DBP) per unit increased the average log FBS level by 0.0005. Secondary and higher education levels lower log FBS levels by 99.41% and 99.45%, respectively, compared with noneducated individuals. ConclusionThe study showed that hypertension history, type of diet, age, status of education, type of drug, body mass index, diastolic blood pressure, and time were statistically significant factors. ImplicationsAccording to the study, eating a healthy diet, maintaining a healthy body weight, and a low blood sugar level are essential to controlling blood sugar and preventing long-term complications. The government should build an educational institution proportional to the population and open programs to increase awareness about the prevention mechanism of diabetes in communities.