This is a prospective cohort study. The main objective is to compare the prevalence of a "full stomach" using gastric ultrasound technique, in elective surgical patients with diabetes mellitus compared to non-diabetic controls following the present fasting guidelines (2 h after clear liquid and 6h after a light meal). For patients with a full stomach, an consecutive ultrasound scan is performed every 30 min,until empty stomach or intermediate stomach contents are detected to determine the mean gastric emptying time for clear liquid and light meal, and to investigate the risk factors for delayed stomach emptying in diabetic patients by logistic regression analysis .