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Carbohydrates are organic molecules constructed in the ratio
(CH2O)n in a variety of lengths and shapes. Carbohydrates
are the body’s preferred source of energy; the other
potential energy sources being proteins and fats. Carbohydrates
are broken down in the body into sugars, starches, and fiber.
The sugars are known as simple carbohydrates, and the starches
and fiber are known as complex carbohydrates. (Alcohol is
also considered a class of carbohydrates but will not be discussed
in this section.)
Function
Carbohydrates perform three important functions in the body:
- Supply energy
- Supply fiber
- Aid in the digestion of fats
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Monosaccharides |
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Disaccharides |
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Polysaccharides |
| Monosaccharides
are the simplest form of carbohydrates. The monosaccharides
are glucose, galactose, and fructose. Sugars and starches
are broken down in the body into the simple sugar glucose.
Glucose is the major sugar found in the bloodstream and
supplies energy for the body. Some body tissues, such
as red blood cells and parts of the brain, are able to
get energy only from glucose. Fructose is found in honey
and fruits and is known as the sweetest of the sugars.
Galactose is not found in nature, but it is one of the
two monosaccharides available after the breakdown of lactose
(milk sugar). |
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Disaccharides
are formed when two monosaccharides are joined together.
They are broken down into their monosaccharide components
during digestion. The disaccharides are sucrose, maltose,
and lactose. Sucrose (glucose + fructose) is found in
white, refined table sugar, brown sugar, confectioner’s
sugar, cane sugar, beet sugar, molasses, and maple syrup.
Maltose (glucose + glucose) is malt sugar which is found
in sprouting cereal grains. Lactose (glucose + galactose)
is milk sugar and is found only in milk. |
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Polysaccharides
are the complex carbohydrates often consisting of very
long chains of glucose monomers. They
include starch, cellulose, and glycogen. Starch is the
most abundant polysaccharide and is an important storage
form of energy in plants. Starch can be found in roots
(such as potatoes), legumes, grains, and vegetables, but
must be broken down into glucose by the body before it
can be utilized. Cellulose is the fibrous material found
in plants, such as the strings in celery, and is commonly
referred to as fiber or roughage. Cellulose cannot be
digested by humans. Sources of cellulose include vegetables,
fruits, and whole grain cereals. Glycogen, also known
as animal starch, is the storage form of carbohydrates
found in the liver and muscles. Glycogen in the liver
is easily broken down into blood glucose, and muscle glycogen
supplies glucose for muscle use. This is especially important
during periods of intense exercise. |
Forty-five to sixty-five percent of calories should come
from complex carbohydrates. Preferred carbohydrate sources
include vegetables, fruits, grains and grain products, legumes,
and dairy products. Current recommendations suggest half of
all grain and grain products consumed should be whole grains.
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