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Chewing for energy

What happens when you chew? How can chewing affect how quickly energy is released from different foods?

What happens when you chew?

Chewing breaks foods into smaller pieces so they can be swallowed. Chewing also adds saliva, which coats the food in digestive enzymes, water, and mucus. Saliva contains the digestive enzyme amylase that breaks down starch into smaller sugars, like glucose and fructose.

The 'chew and spit' test

How do you measure the size of bits of chewed food? There is a simple way of doing this. People are asked to chew their food and spit it out when they would normally swallow it. The chewed food particles can then be separated by size using a stack of sieves with different sizes of mesh. It's messy, but it works!

Researchers in the Lifestyle Food programme have made a machine that can replicate some chewing actions.

Particle size matters

Most people chew the same foods to about the same size. This is important because the size of the food particle affects the time it takes to digest. Larger particles take a long time to digest, which means energy is released slowly from the food and it has a low glycaemic load. Smaller particles are quickly digested and have a high glycaemic load.

What changes the way we chew?

The food structure, density, shape, and surface area will all affect the way we chew food. For example, pasta and white bread both have similar ingredients, but energy is released from these foods at different rates. This is because pasta is wet and slippery and isn't chewed much before it is swallowed - so it has a low glycaemic load. Whereas, white bread is drier and is chewed a lot before it is swallowed - so it has a high glycaemic load.

Changing chewing

Scientists in the Lifestyle Foods programme are researching ways to alter the rate that energy is released from foods. One way they are doing this is to vary food structure and composition, as this changes the amount a food is chewed and the rate at which energy is released from the food.

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