Following the 75g drink consisting of 75g glucose and 150 mg of 13C-acetate made up to 300 ml with water, at t = -3 minutes, and every 5 minutes between t = 0 - 60, followed by every 15 minutes between t = 60 - 180, breath samples will be collected in sealed tubes for subsequent analysis of 13CO2 for measurement of gastric emptying.