What are the main types of carbohydrates?

Carbohydrates are molecules made from carbon, hydrogen and oxygen in the proportions C (H20) which gives the name carbo-hydrate.  The simplest form are ‘monosaccharide’ sugars, which contain the equivalent of 6 carbon atoms and 6 water molecules. They can then be joined together in different ways to form carbohydrates with anything between two (di-saccharides) and many thousands (poly-saccharides) of six-carbon sugar units.

Carbohydrates are made in plants by the process of photosynthesis, which captures energy (measured in calories) from sunlight to make a sugar (glucose) from carbon dioxide in air and water.  The energy that is stored in the glucose molecule is released when it is metabolised, to be used for all the functions of the plant, or of an animal which eats it.

  • A carbohydrate with only one 6-carbon sugar unit is called a simple sugar or a monosaccharide. Fructose, glucose and galactose are three examples. A carbohydrate with two sugar units is called a disaccharide. As common examples, sucrose is made from glucose and fructose (found in fruit), and lactose (found in milk) is made from glucose and galactose.
  • Complex carbohydrates, or polysaccharides. are carbohydrates with three or more sugar units joined together.  These take longer to digest, so they are better for a slow energy release.  The smaller carbohydrate with three to eight sugar units joined together can be called an oligosacharide.  In plants the polysaccharide used to store energy is starch, sometimes in large amounts (eg in potatoes).  In animals, starch is not present, and what little carbohydrate is stored as polysaccharide is as glycogen, in the liver and muscle.  Good examples of complex carbohydrates are porridge, vegetables and whole grains.