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NUTRITION
- CARBOHYDRATES |
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Carbohydrates
are the human body’s key source of energy, providing
4 calories of energy per gram. |
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When carbohydrates are broken down by the body,
the sugar glucose is produced; glucose is critical
to help maintain tissue protein, metabolize fat,
and fuel the central nervous system. |
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Glucose
is absorbed into the bloodstream through the intestinal
wall. Some of this glucose goes straight to work in
our brain cells and red blood cells, while the rest
makes its way to the liver and muscles, where it is
stored as glycogen (animal starch), and to fat cells,
where it is stored as fat. Glycogen is the body’s
auxiliary energy source, tapped and converted back into
glucose when we need more energy. Although stored fat
can also serve as a backup source of energy, it is never
converted into glucose. |
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Fructose and galactose, other sugar products resulting
from the breakdown of carbohydrates, go straight
to the liver, where they are converted into glucose.
Starches and sugars are the major carbohydrates.
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Common starch foods include whole-grain breads and cereals,
pasta, corn, beans, peas, and potatoes. Foods that contain
starches and naturally occurring sugars are referred
to as complex carbohydrates, because their molecular
complexity requires our bodies to break them down into
a simpler form to obtain the much-needed fuel, glucose.
Our bodies digest and absorb complex carbohydrates at
a rate that helps maintain the healthful levels of glucose
already in the blood. |
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In
contrast, simple sugars, refined from naturally
occurring sugars and added to processed foods,
require little digestion and are quickly absorbed
by the body, triggering an unhealthy chain of
events. The body’s rapid absorption of simple
sugars elevates the levels of glucose in the blood,
which triggers the release of the hormone insulin. |
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Insulin
reins in the body’s rising glucose levels, but
at a price: Glucose levels may fall so low within one
to two hours after eating foods high in simple sugars,
such as candy, that the body responds by releasing chemicals
known as anti-insulin hormones. This surge in chemicals,
the aftermath of eating a candy bar, can leave a person
feeling irritable and nervous. |
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Many
processed foods not only contain high levels of
added simple sugars, they also tend to be high
in fat and lacking in the vitamins and minerals
found naturally in complex carbohydrates. |
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| Nutritionists
often refer to such processed foods as junk foods and
say that they provide only empty calories, meaning they
are loaded with calories from sugars and fats but lack
the essential nutrients our bodies need.
In addition to starches
and sugars, complex carbohydrates contain indigestible
dietary fibers. Although such fibers provide no energy
or building materials, they play a vital role in our
health. Found only in plants, dietary fiber is classified
as soluble or insoluble. Soluble fiber, found in such
foods as oats, barley, beans, peas, apples, strawberries,
and citrus fruits, mixes with food in the stomach and
prevents or reduces the absorption by the small intestine
of potentially dangerous substances from food. Soluble
fiber also binds dietary cholesterol and carries it
out of the body, thus preventing it from entering the
bloodstream where it can accumulate in the inner walls
of arteries and set the stage for high blood pressure,
heart disease, and strokes. |
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Insoluble
fiber, found in vegetables, whole-grain products,
and bran, provides roughage that speeds the elimination
of feces, which decreases the time that the body
is exposed to harmful substances, possibly reducing
the risk of colon cancer. |
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Studies
of populations with fiber-rich diets, such as Africans
and Asians, show that these populations have less risk
of colon cancer compared to those who eat low-fiber
diets, such as Americans. In the United States, colon
cancer is the third most common cancer for both men
and women, but experts believe that, with a proper diet,
it is one of the most preventable types of cancer. |
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Nutritionists caution that most Americans need
to eat more complex carbohydrates. In the typical
American diet, only 40 to 50 percent of total
calories come from carbohydrates—a lower
percentage than found in most of the world. To
make matters worse, half of the carbohydrate calories
consumed by the typical American come from processed
foods filled with simple sugars. |
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Experts
recommend that these foods make up no more that 10 percent
of our diet, because these foods offer no nutritional
value. Foods rich in complex carbohydrates, which provide
vitamins, minerals, some protein, and dietary fiber
and are an abundant energy source, should make up roughly
50 percent of our daily calories. |
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"Human
Nutrition."Microsoft® Encarta® Encyclopedia
2001. © 1993-2000 Microsoft Corporation. All rights
reserved. |
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