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Testing food energy

The Lifestyle Foods programme is about making foods to suit different lifestyles. Testing how quickly energy is released from different foods is a key part of this.

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.

The level of glucose in a person's blood is measured using a hand-held spectrophotometer.

Testing of different foods is often done in 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.

These participants 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 working on the Lifestyle Foods programme 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. What are the advantages and disadvantages of testing the effects of foods on blood glucose in vitro versus in vivo?

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.

Get information sheet: Chewing for energy

Get video: Testing glycaemic load
Get video: Measuring blood glucose

A machine that can replicate some of the actions involved in chewing has been developed to test new foods for the Lifestyle Foods programme. A university student was very involved in making this machine.

The digestion model

Researchers have 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.

Testing the taste

Consumer research is an important part of developing new foods. Scientists in the Lifestyle Foods programme use sensory testing to find out consumers likes and dislikes. All of the sensory attributes of a food are rated including taste, smell, texture and chewiness. This helps the Lifestyle Foods team to design and make foods that taste great and people will enjoy eating.

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