What are carbohydrates?

  • Carbohydrates are compounds that are found in living things. Their molecules are made up of carbon, hydrogen and oxygen atoms.
  • Carbohydrates are an important source of energy in a healthy diet. Starchy and sugary foods are high in carbohydrates.
  • Athletes eat different types of carbohydrate at different times in their training schedules.
Get a lesson in carbohydrates from Team GB cyclist Mark Stewart.

What are carbohydrates?

The main types of carbohydrates are:

  • Simple carbohydrates (also known as sugars)

The basic units of carbohydrates are simple sugar molecules, for example glucose, fructose and sucrose. They are provided by sweet foods like chocolate, milk and fruit.

  • Complex carbohydrates (also known as starch)

These are formed of long chains of sugars joined together. They are found in foods like bread, rice, pasta and potatoes.

How does your body use carbohydrates?

Carbohydrates are an important source of energy. They fuel the processes in your body.

Carbohydrates are broken down by the body into glucose, which can be absorbed into the bloodstream.

Once absorbed, glucose molecules travel in the blood to the body's cells where they are used for respiration. The glucose reacts with oxygen, releasing energy.

Starch and sugars are digested differently by the body:

  • Sugary foods and drinks can be quickly broken down to make glucose. This can be quickly absorbed into the bloodstream to provide a short-lasting energy boost.

  • Starch is a long, complex molecule which is harder to break down into glucose. This means that it releases energy more slowly. As such, it is known as a slow-release carbohydrate.

The glucose molecule is a high-energy carbohydrate and used in respiration.
During digestion, long chains of starch molecules break down into small glucose molecules by reacting with water.

How much do you need?

The World Health Organisation recommends getting half your energy from carbohydrates. For a moderately active teenager, this is about 260 g daily.

It is important to eat enough carbohydrates. However, too many carbohydrates can contribute to weight gain.

Who needs to know about carbohydrates?

Athletes need different types of carbohydrate for different situations.

Before a short race, an athlete might eat a sweet banana for an ‘energy boost’.

Before a long training session an athlete might eat plenty of starchy pasta for a steady supply of energy.

We use the energy released by respiration to move, grow and repair damaged tissue.

Carbohydrates quiz

Find out how much you know in the quick science quiz!

Where next?

Discover more about this topic from around Bitesize.

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