This testing is about how long it takes for food to be emptied from your stomach, which can be effected by a number of factors for example how well food is chewed. The larger the piece of food swallowed the slower the food is emptied from the stomach. Normal gastric emptying after a meal takes around 1 hour 30 mins to 2 hours. While gastric emptying studies are commonly used to investigate digestion and associated conditions they can also be used to explain the effect of glycemic response as the slower rate of the stomach emptying impacts the rate of absoprtion in the small intestines. Certain components in food can increase the time it takes for gastric emptying, and this has been linked with increased satiety and potentially weight loss.
By labelling foods with stable isotopes (most commonly C13), and the using mass spectroscopy techniques to measure the presence of these isotopes for three hours post consumption, it is possible to track the rate of absorption of the isotope, and therefore the food component in to the body. This can be done with both breath and plasma samples.