Both human and laboratory-based tests are used to measure how quickly energy is released from a food.
Carbohydrates for energy
Carbohydrates are the most common source of energy in our diet. They are found in bread, pasta, beans, potatoes, bran and cereals. Starch is a complex form of carbohydrate. When starches are processed during digestion, they are changed into a sugar called glucose. The glucose is then released from the small intestine into the blood. This glucose is converted by cells and used for energy.
Different foods for different energy
The rate at which energy is released from a food depends on food structure, density, shape and surface area. The rate at which energy is released from a particular food is known as the glycaemic load. The glycaemic load is a measure of how quickly or slowly a food changes blood sugar levels.
Measuring the glycaemic load
The glycaemic load of a food can be calculated by measuring how quickly glucose is released when a standard serving of a particular food is eaten. The most obvious way to do this is to have people agree to eat a certain food and then have blood samples taken at regular intervals.
Testing of different foods is often done using the same person to give a fair comparison between foods. More than one person also needs to be tested because of the variability between people.
Participants who do this are part of a clinical trial. They need to understand what they are being asked to do and any risks that might be involved. They then need to agree to participate in all the processes involved in the testing. This process is called giving informed consent.
The problem with people
Because of the variability between people, many different people need to be tested using the same foods. This becomes very costly and time consuming. To overcome this problem, scientists have devised models of both chewing and digestion to provide a cheaper and faster alternative to human testing. Testing that is done like this, in a laboratory, is called in vitro testing. Testing that is done using live participants (human or animal) is called in vivo testing.
The chewing machine
Chewing is an important first step in digestion. People chew their food to break it up into smaller pieces that can be comfortably swallowed. The size of chewed food particles also affects how quickly the food is digested, changing its glycaemic load.
A machine that can replicate some of the actions involved in chewing was developed to test new foods. A university student was very involved in making this machine. The article Chewing for energy explains how the model works.
The digestion model
Researchers also developed a model of digestion that reproduces exactly what goes on in human digestion. Just like our digestive system, the food in the model is kept warm, is moved around and is treated with digestive chemicals and enzymes, and just like our digestive system, glucose is produced and can be measured.
Nature of science
Robotics like the chewing machine and use of models to simulate the digestive systems reduce some of the costs associated with product development and testing, but the machines must be validated – tested to make sure the machine-derived data matches up with measurements taken with real humans.
Plant & Food Research scientist Dr John Ingram used a clinical trial to test the bitter plant ingredient Amarasate extract on appetite suppression. Read about it in the article Plant extract hailed as key to fighting fat epidemic.
This podcast, from Plant & Food Research, features Dr Edward Walker, one of the lead scientists involved in discovering Amarasate™.