Surgical patients are usually starved for 8 hours before operation in order to ensure the stomach is empty and thus reduce the chances of vomiting during the anaesthetic. Recent studies have shown that this period of starvation is harmful as it 'weakens' the body before operation. To avoid the harmful effects of starvation, patients are now given carbohydrate (sugar-containing) drinks 2 to 4 hours before surgery. These drinks have been shown to make patients feel better, reduce sickness after the anaesthetic/surgery and result in a quicker recovery from operation. The optimum time of giving these drinks to patients before operation is unknown. Previous studies have shown that the drinks empty from the stomach within 2 - 4 hours depending on their ingredients. The investigators would like to study the effects of adding protein and fat to these drinks on how quickly the drinks empty from the stomach. This study will investigate the hormone responses of the body following intake of 3 different drinks in order to determine the mechanisms that underlie the control of stomach emptying. This information will also allow us to improve the design of these drinks and this could help patients who undergo surgery who receive them.