['Obesity has been associated with gastroesophageal reflux disease (GERD) and its complication, but the mechanism is unclear. We evaluated the association between obesity and function of lower esophageal sphincter (LOS) in subjects without GERD.', 'We prospectively recruited consecutive obese (BMI >30) patients referred for weight reduction procedure and age- and sex-matched overweight (BMI 25-30) and normal weight (BMI > or =20 and <25) subjects. Exclusion criteria included esophagitis, reflux symptoms, use of proton pump inhibitor, hiatus hernia >2 cm, and diabetes mellitus with microvascular complication. All participants underwent combined 2-hour postprandial esophageal manometry and pH monitoring after a standard test meal followed by 24-hour ambulatory pH monitoring.', 'Eighty-four subjects (obese, 28; overweight, 28; normal weight, 28) were studied. All 3 groups had comparable mean LOS pressure, LOS length, and peristaltic function. During the postprandial period, both obese and overweight groups had substantial increase in 2-hour rate of transient lower esophageal sphincter relaxation (TLOSR) (normal weight: 2.1 +/- 1.2 vs overweight: 3.8 +/- 1.6 vs obese: 7.3 +/- 2.0, P < .001), proportion of TLOSR with acid reflux (normal weight: 17.6% +/- 22.0% vs overweight 51.8% +/- 22.5% vs obese: 63.5% +/- 21.7%, P < .001), and gastroesophageal pressure gradient (GOPG) (normal weight: 4.5 +/- 1.2 mm Hg vs overweight: 7.1 +/- 1.4 mm Hg vs obese: 10.0 +/- 1.5 mm Hg, P < .001). Using multiple regression model, BMI (r(2): 0.70, B: 0.28, 95% CI: 0.24-0.33, P < .001) and waist circumference (r(2): 0.65, unstandardized regression coefficient [B]: 0.10, 95% CI: 0.08-0.11, P < .001) were significantly correlated with TLOSR.'] Is obesity associated with increased transient lower esophageal sphincter relaxation?