Carbohydrates for energy
Carbohydrates are obtained from grains, bread, rice, and pasta, as well as from fruits, vegetables, pulses, and dairy products.
Variable complexity
© DK
All carbohydrates are composed of chains of sugar molecules. Those composed of just one or two sugar molecules are known as simple carbohydrates, and are divided into monosaccharides and disaccharides. Monosaccharides include glucose, which is present in the blood; fructose, which is found in fruits; and galactose, which is found in dairy products. Disaccharides include sucrose (table sugar) and lactose (the primary sugar present in milk).
Complex carbohydrates, also called polysaccharides, are composed of many simple-sugar molecules that are linked together. Examples of complex carbohydrates include starch, which gives potatoes and grains their hearty character; glycogen, which the body stores as a source of energy; and dietary fibre.
Why do we need them?
Carbohydrates provide energy for all the body's activities. As they are digested, carbohydrates are broken down into simple sugars, such as glucose. Glucose supplies energy for most of the body's activities, and in some cells and tissues such as red blood cells and the brain it is the sole source of energy.
Carbohydrates are needed for building the non-essential amino acids that the body uses to create proteins (see Good protein sources). They also help in the processing of fat and in the building of cartilage, bone, and tissues of the nervous system.
Choosing carbohydrates
As the major source of energy, carbohydrates must form a large part of your diet, but you should choose the best types to optimize your health. This means eating a wide variety of different types of grains, fruits, and vegetables. As far as possible, try to eat whole grains and products made from unrefined grains in preference to refined varieties. In this way, you will benefit from the nutrients and fibre that are removed during the refining process (see Refined grains).
Some researchers believe that the glycaemic index (GI) provides a useful guide to the best carbohydrates, and that low-GI foods, which release sugar more slowly into the blood, are of particular benefit to people with diabetes and insulin resistance. However, we believe that while the concept of the glycaemic index is interesting, it should not be relied on as the sole indicator of a carbohydrate's healthfulness. Nutritional content and fibre are also important and these should be borne in mind when choosing carbohydrates.
Jargon buster
Insulin resistance
A reduced sensitivity in the tissues of the body to the action of the hormone insulin. As a result of this sensitivity, blood glucose does not enter those tissues to be used as a source of energy, so blood glucose levels remain abnormally high. The condition is found frequently in overweight and obese people.
Lisa Hark, PhD RD & Dr Darwin Deen
Nutrition for Life Copyright © 2005 Dorling Kindersley Text copyright © 2005 Lisa Hark and Darwin Deen
Posted 30.06.2010
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