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NUTRITION
- PROTIENS |
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Dietary
proteins are powerful compounds that build and repair
body tissues, from hair and fingernails to muscles.
In addition to maintaining the body’s structure,
proteins speed up chemical reactions in the body, serve
as chemical messengers, fight infection, and transport
oxygen from the lungs to the body’s tissues. Although
protein provides 4 calories of energy per gram, the
body uses protein for energy only if carbohydrate and
fat intake is insufficient. When tapped as an energy
source, protein is diverted from the many critical functions
it performs for our bodies. |
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Proteins are made of smaller units called amino
acids. Of the more than 20 amino acids our bodies
require, eight (nine in some older adults and
young children) cannot be made by the body in
sufficient quantities to maintain health. These
amino acids are considered essential and must
be obtained from food. |
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When
we eat food high in proteins, the digestive tract breaks
this dietary protein into amino acids. Absorbed into
the bloodstream and sent to the cells that need them,
amino acids then recombine into the functional proteins
our bodies need. |
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Animal proteins, found in such food as eggs, milk,
meat, fish, and poultry, are considered complete
proteins because they contain all of the essential
amino acids our bodies need. Plant proteins, found
in vegetables, grains, and beans, lack one or
more of the essential amino acids. |
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However,
plant proteins can be combined in the diet to provide
all of the essential amino acids. A good example is
rice and beans. Each of these foods lacks one or more
essential amino acids, but the amino acids missing in
rice are found in the beans, and vice versa. So when
eaten together, these foods provide a complete source
of protein. Thus, people who do not eat animal products
(see Vegetarianism) can meet their protein needs with
diets rich in grains, dried peas and beans, rice, nuts,
and tofu, a soybean product. |
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Experts
recommend that protein intake make up only 10
percent of our daily calorie intake. Some people,
especially in the United States and other developed
countries, consume more protein than the body
needs. Because extra amino acids cannot be stored
for later use, the body destroys these amino acids
and excretes their by-products. |
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Alternatively,
deficiencies in protein consumption, seen in the diets
of people in some developing nations, may result in
health problems. Marasmus and kwashiorkor, both life-threatening
conditions, are the two most common forms of protein
malnutrition. |
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health conditions, such as illness, stress, and
pregnancy and breast-feeding in women, place an
enormous demand on the body as it builds tissue
or fights infection, and these conditions require
an increase in protein consumption. |
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example, a healthy woman normally needs 45 grams of
protein each day. Experts recommend that a pregnant
woman consume 55 grams of protein per day, and that
a breast-feeding mother consume 65 grams to maintain
health. |
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A
man of average size should eat 57 grams of protein
daily. To support their rapid development, infants
and young children require relatively more protein
than do adults. A three-month-old infant requires
about 13 grams of protein daily, and a four-year-old
child requires about 22 grams. |
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Once
in adolescence, sex hormone differences cause boys to
develop more muscle and bone than girls; as a result,
the protein needs of adolescent boys are higher than
those of girls. |
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"Human
Nutrition."Microsoft® Encarta® Encyclopedia
2001. © 1993-2000 Microsoft Corporation. All rights
reserved. |
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