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Protein
Definition
Proteins are complex organic compounds. The
basic structure of protein is a chain of amino acids.
Function
Protein is the main component of muscles,
organs, and glands. Every living cell and all body fluids,
except bile and urine, contain protein. The cells of
muscles, tendons, and ligaments are maintained with protein.
Children and adolescents require protein for growth and
development.
Food Sources
Proteins are described as essential and
nonessential proteins or amino acids. The human body
requires approximately 20 amino acids for the synthesis of
its proteins.
The body can make only 13 of the amino acids -- these are
known as the nonessential amino acids. They are called
non-essential because the body can make them and does not
need to get them from the diet. There are 9 essential amino
acids that are obtained only from food, and not made in the
body.
If the protein in a food supplies enough of the essential
amino acids, it is called a complete protein. If the protein
of a food does not supply all the essential amino acids, it
is called an incomplete protein.
All meat and other animal products are sources of complete
proteins. These include beef, lamb, pork, poultry, fish,
shellfish, eggs, milk, and milk products.
Protein in foods (such as grains, fruits, and vegetables)
are either low, incomplete protein or lack one of the
essential amino acids. These food sources are considered
incomplete proteins.
Plant proteins can be combined to include all of the
essential amino acids and form a complete protein. Examples
of combined, complete plant proteins are rice and beans,
milk and wheat cereal, and corn and beans.
Side Effects
A diet high in meat could lead to high
cholesterol or other diseases, such as gout. Another
potential problem is that a high-protein diet may put a
strain on the kidneys. Extra waste matter, which is the end
product of protein metabolism, is excreted in the urine.
Recommendations
A nutritionally balanced diet provides
adequate protein. Vegetarians are able to get enough protein
if they eat the proper combination of plant proteins.
The amount of recommended daily protein depends upon age,
medical conditions, and the type of diet one is following.
Two to three servings of protein-rich food will meet the
daily needs of most adults.
The following are the recommended serving sizes for protein:
-
For recommended serving sizes of
protein for children and adolescents, see age
appropriate diet for children 2 to 3 ounces of cooked
lean meat, poultry, and fish (a portion about the size
of a deck of playing cards) 1/2 cup of cooked dry beans,
lentils, or legumes 1 egg or 2 tablespoons of peanut
butter, which count as 1 ounce of lean meat
Select lean meat, poultry without skin,
fish, and dry beans, lentils, and legumes often. These are
the protein choices that are the lowest in fat. For more
information, see the food guide pyramid.
[Retrieved from http://www.nih.gov]
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