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Carbohydrates (also see Energy production)
The collective name given to starches, glycogen, sugars and
dietary fibres which can be converted to glucose and used as fuel for energy.
They are classified as monosaccharides and disaccharides (simple carbohydrates
or sugars), polysaccharides (starches, glycogen and fibre), and oligosaccharides
(carbohydrates which fall somewhere in between sugars and starches, or are
formed during the digestion of polysaccharides).
Chemically speaking, carbohydrates consist of various combinations of
carbon, hydrogen and oxygen, and are classified into three main groups,
according to their complexity. Least complex are the monosaccharides and
disaccharides (also known as the sugars), and most complex are the
polysaccharides (also known as starch or complex carbohydrate).
Carbohydrates come from plants, which store them as their chief source of
energy. Water, minerals and nitrogen in the soil are taken up by the plant's
roots and sent to the leaves. With the aid of chlorophyll, these nutrients
combine with carbon dioxide and sun energy to form sugars via photosynthesis.
The most common of all the sugars is sucrose, or ordinary table sugar.
Like lactose and maltose, sucrose is a disaccharide, which simply means a
combination of two simple sugars, or monosaccharides. Common sugars and their
sources are shown in the table:
Disaccharides are broken down into their component monosaccharides by the processes of digestion. As we can see, all disaccharides have a glucose component. A daily supply of glucose is needed for all the body's metabolic functions. The end product of starch digestion is also mainly glucose. Starches may be fully or partially digestible, or completely indigestible, depending on the type. They are found in grains, roots, vegetables and pulses, encased within plant cells. Cooking softens and ruptures the plant cell to make the starch available for enzymes to work on in our intestines. Once sugars and starches have been broken down into monosaccharides by the digestive processes, the monosaccharides enter the bloodstream and travel to the liver, where those that are not already glucose are converted into glucose and released into the circulation. Within 30 minutes to one hour after a meal, the blood glucose peaks. High blood glucose (blood sugar) levels stimulate the production of the hormone insulin by the pancreas. Insulin encourages the uptake of glucose from the blood into the body's muscle and fat cells, where it goes through successive chemical changes. Energy is released when the end products of glucose are combined with oxygen. Adapted from the Nutritional Health Bible by Linda LazaridesDownload the whole database |
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