Carbohydrates are essential energy carriers, just like fats. They provide the body with a source of fuel and energy that is required to carry out daily activities and exercise. Carbohydrates in the form of glucose provide us with immediate energy. Once the glucose is made from the carbohydrates it gets into the bloodstream so that your organs, cells and brain can use it for energy. Other body cells are also able to burn fats.


Photosynthesis is the process by which plants use the energy from sunlight to produce sugar. The raw materials are carbon dioxide (CO2) and water (H2O); the energy comes from sunlight. The conversion of unusable sunlight energy into usable chemical energy for the formation of glucose is associated with the actions of the green pigment chlorophyll. The process is a crucial biochemical pathway because it gives off oxygen, which all life depends upon.

Plants cannot store up lots of glucose. The extra glucose that the plant does not need for its own life process is converted into starch (as for instance in potatoes). When plants need to use the energy, they can turn the starch back into glucose. The carbohydrates stored by plants are a rich source of food and energy for all life on earth, as we cannot produce these substances ourselves.

Carbohydrates consist of carbon (C), hydrogen (H) and oxygen (O). Contrary to proteins and fats they do not contain any other elements. The name is derived from ‘carbon’ and the Greek word for water: hydros. We also call them sugars or saccharides. The molecules of saccharides can contain small (minimal 3) or large (up to 25.000) amounts of carbon atoms.

6 CO2 + 6 H2O ---light---> C6H12O6 + 6 O2

Chemical structure of carbohydrates

Chemically speaking, saccharides (carbohydrates) can be divided into three groups, from single small molecules to large and complex structures.

  • Monosaccharide are the most basic units of carbohydrates, the simplest form of sugar and the building blocks for all other carbohydrates. Well-known examples are glucose (dextrose) and fructose (fruit-sugar). Monosaccharide is an important energy source for the body, which is made through photosynthesis. Glucose is typically found in sweet fruits (grapes, honey). In dry form it is a white substance with a less sweet taste than for instance regular sugar (sucrose). Fructose is less common. Important sources of fructose are honey and figs. Fructose is twice as sweet as regular sugar. Galactose is an important component of the disaccharide lactose (milk-sugar), which consists of one molecule galactose and one molecule glucose. Galactose is secreted by the mammary glands; it is not present in plants.
  • Disaccharide are formed by two monosaccharides linked by a glycosidic bond. The most familiar example is table sugar. The chemical name of this sugar is sucrose but it is also sometimes called saccharose. Table sugar comes from plant sources such as sugarcane and sugar beet. It has a very sweet taste. Lactose is another type of sugar that is naturally present in milk. Contrary to table sugar, lactose does not taste sweet. One glass of milk contains approximately 9 gram of lactose. This is more or less the same amount as two spoonfuls of sugar. Even though it doesn’t taste sweet, it still contains the same amount of calories.
  • Polysaccharide is a carbohydrate containing large numbers of monosaccharides (usually more than 20). A polysaccharide is generally not water-soluble, nor does it taste sweet. Examples are starch, glycogen and fibers (cellulose, pectin). Glycogen is the main form of carbohydrate storage in animals and humans. One molecule of glycogen can consist of 3.000 to 60.000 molecules of glucose. Contrary to vegetable starch, glycogen is water-soluble.

The glycemic index

Glucose is fuel for the body. All our cells need glucose in order to function properly. As glucose is carried around in our body by the bloodstream, our blood always contains a certain amount of glucose. We call this the blood sugar level or glycemic level. Insulin and glucagon are the hormones that maintain blood glucose within a narrow range. Fluctuations outside of the normal desired range can lead to a number of symptoms including feeling thirsty, craving for food, water retention, and mood swings. When too much insulin is produced, for instance after a sugar-rich meal, the excess of glucose in the blood is converted into glycogen, which is stored in the liver and muscles.

‘Good’ and ‘bad’ carbohydrates

The carbohydrates we consume have a major impact on the blood sugar level. The glycemic index (GI) is a measure of the effects of carbohydrates in food on blood sugar levels. Carbohydrates with a high GI are rapidly absorbed by the body and cause a more rapid rise in blood glucose levels. They are sometimes called ‘bad’ or ‘fast’ carbs. Carbohydrates with a low GI are broken down and absorbed by the body more slowly. They hardly cause any rise in blood sugar levels and are also called ‘good’ or ‘slow’ carbs. Typical examples of foods with ‘bad’ carbs are sugar, honey, potatoes, white rice and bread, cookies and pastry. Examples of ‘good’ carbs are fresh fruit, beans, lentils, fresh vegetables, peanuts and dairy products.