Protein
    Protein has a stucture made of carbon, hydrogen, and oxygen, just like fats and
carbohydrates do. But, protein also contains nitrogen, which makes up about 16%
of the protein structure. These four elements combine into several different forms
of amino acids. Amino acids have one amino group and one acid group. The rest
of being differing combinations of carbon, hydrogen, oxygen, and sometime even
sulfer. There are twenty amino acids which combine in several ways to make the
proteins needed for structures and functions in the human body. Carbohydrates
provide energy to cells, while protein provide the material needed to build and
grow the body's tissues.
    A protein is created when two amino acids link together to form a peptide bond,
the result is a dipeptide. As more amino acids join the chain, a polypeptide is
formed. Most proteins are polypeptides, sometimes combining up to 300 amino
acids. All twenty of the human body's amino acids are listed below and must be
present at the same time for protein synthesis.

    Essential Amino Acids
            Essential amino acids are those that cannot be formed in the body and must
            be ingested. These include: Histidine, Isoleucline, Leucine, Lysine,
            Methionine, Phenylalanine, Threonine, Tryptophan, and Valine.
    Non-Essential Amino Acids
            Non-essential amino acids are considered dispensible by the body because
            the human body is capable of forming these amino acids on it's own. A list
            of non-essential amino acids includes: Alanine, Arginine, Asparagine,
            Aspartic Acid, Cysteine, Glutamic Acid, Glutamine, Glycine, Proline,
            Serine, and Tryosine.

    Generally, foods that contain all nine essential amino acids are considered
complete proteins, or high-quality proteins. Those missing one or more of the nine
essential amino acids are considered incomplete proteins. Those proteins found in
animal foods are regarded as higher-quality than in plants. Although plant proteins
are seen as lower-quality, they may still provide all the protein and amino acids
needed for growth.
    The digestive system breaks down proteins back into their amino acid groups
so they can enter the blood stream. Once there, they will be carried to the liver.
While the digestion of proteins may take several hours, once the amino acids are in
the blood stream they will be cleared in 5-10 minutes. The liver then redistributes
them as free amino acids. Cells obtaining the amino acids out of the blood will use
the DNA in the nucleus to direct the building of the proteins it specifically needs
for growth or reproduction. The cells will only use the amount of amino acids to
meet their present needs. They are unable to store extra amino acids due to the
body's inability to store nitrogen. Deamination is the process which removes the
amino group (contains nitrogen) is removed from the chain, leaving a substance
known as alpha-ketoacid. The nitrogen removed is taken to the liver and made
into ammonia, which then converts to urea and is eliminated through urine. The
resultant alpha-ketoacids are converted to glucose, acetyl CoA, or stored as
fat.

    Protein is important in the regulation of human metabolism. It is used in
forming almost all enzymes, many horomones, and other significant compounds.
It is the main ingredient used in forming all body tissues, such as muscle. For
this reason protein intake is vital during period of rapid growth like childhood
and adolesence. It is also vital to people attempting to grow muscle and must
be continously ingested, without excess which will turn into fat. Proteins are
also carriers in the blood stream for free fatty acids and lipoproteins.


Nutrition Basics
Fats
Carbohydrates