What are carbohydrates and sugar?
On average half of the dietary energy we consume comes from carbohydrates - a complex group of compounds made of carbon, hydrogen and oxygen. Carbohydrates almost exclusively come from plants, the exception being lactose from milk and a small number of sugars in red meat. When consumed, carbohydrates provide energy to our cells.
Carbohydrates can be split into several groups based on their chemical structure and complexity. The three most common groups are outlined below. Sugars, a carbohydrate, falls into the first two groups.
Monosaccharides are single sugar molecules that are the building blocks for all other sugars and carbohydrates. Glucose, fructose and galactose are examples of these (see figure).
Monosaccharides include glucose, galactose and fructose - all commonly found in food.
Disaccharides are sugars that are made up of two single sugar units joined together. Lactose, the main sugar found in milk, is a disaccharide, consisting of a galactose and a glucose molecule. Table sugar (sucrose), which is extracted from sugar cane, is another example. Sucrose is made of one glucose and one fructose unit joined together.
Other types of carbohydrates are made up of long chains of molecules with combinations of monosaccharides and disaccharides, and some have very complicated structures. These are known collectively as polysaccharides. They can range from 10 monomers to thousands of monomers. Examples of such carbohydrates are the groups including starch, cellulose, pectin, gums, and fibre. Polysaccharides may not be completely digested by enzymes within the body. They may require fermentation by colonic bateria.
Polyols are alcohols of sugars. They are found naturally in some fruits and vegetables but are usually made commercially. An example is xylitol which is added to sugar free chewing gums, as sugar alcohols do not harm the teeth.