PROTEIN QUALITY:   ARE YOU CONFUSED?

Protein quality is measured a few different ways: Biological Value (BV), Protein Efficiency Ratio (PER), and the newest one called Protein Digestability Corrected Amino Acid Score (PDCAAS) ... whew, that's a mouth full!   We see a lot of words written today about PER cause it's a convenient way to "dumb it down" (make it simple) so everybody has an easy way to know how much protein they need. But, what else do you need to know?   Here's the scoop . . .

Many people confuse amino acids and proteins or believe they are synonymous.   Amino acids are the building blocks of proteins.   A protein is a chemical compound that contains the same atoms as carbohydrates and fats, which are carbon, hydrogen, and oxygen -- but protein is different in that it also contains nitrogen.  These carbon, hydrogen, oxygen and nitrogen atoms are arranged into amino acids, which are linked into chains to form proteins.

There are 22 amino acids important to human nutrition.  Nine of these are essential amino acids -- meaning the body CANNOT make them. Instead they need to be provided from the foods we eat.   The body CAN produce the other 13.  The role of protein in food is not to provide our bodies with proteins directly, but to supply the amino acids from which the body can make its own protesin.   When we eat foods that supply each essential amino acid in adequate amounts, our body supports protein synthesis.

The following lists the amino acids, including the nine essential amino acids, that make up proteins in human nutrition.

Essential Amino Acids:
-- Isoleucine
-- Leucine
-- Lysine
-- Methionine
-- Phenylalanine
-- Threonine
-- Tryptophan
-- Valine
-- Histidine [conditional]


Other Amino Acids:
-- Alanine
-- Arginine
-- Asparagine
-- Aspartic Acid
-- Cysteine
-- Glutamic Acid
-- Glutamine
-- Glycine
-- Proline
-- Serine
-- Tyrosine

To make protein, cells must have all the needed amino acids available simultaneously. Therefore, to make proteins the first important characteristic of protein in our diet is that it should supply at least the nine essential amino acids for the synthesis of others.   If one amino acid is supplied in an amount smaller than needed, the total amount of protein that can be synthesized from others will be limited.

It is impossible to produce a partial protein.   Only complete ones can be made.  Therefore, an eating regimen that contains an imbalance of amino acids will have poor protein quality. When the body attempts to use the amino acids supplied from foods that contain incomplete amino acids, it wastes many amino acids.  In the absence of one amino acid, it can't use the others (creating the "Limited Amino Acid" concept Sports Nutrition Specialists learn about in the internationally accredited SNS course) and the body has no place to store them.

Each food has its own characteristic amino acid balance, and when foods are combined appropriately, they will almost always supply plenty of essential amino acids.   In countries where protein is scarce and/or only one protein rich food is eaten regularly, the quality of that particular food's protein is crucially important to the people's health and particularly important to the children's development.

What is a complete protein?   It is one that contains all the essential amino acids in about the same amount the human body requires -- and it may or may not contain all of the other amino acids the body CAN make (non-essential amino acids).   People generally associate complete protein with such foods as meats and eggs, but not with plant foods.

Why is that?   Because generally proteins derived from animal foods such as meat, fish, poultry, eggs, and dairy products are a complete source of protein.  Those derived from plant foods such as vegetables, grains, and beans vary more than meat and dairy.   If you derive most or all of a days food energy from rice or potatoes, for example, you will not obtain all of the needed essential amino acids needed to maintain a strong, healthy body.  However when two plant proteins, each containing the amino acids that the other lacks, are eaten at the same meal, they can make up an acceptably complete protein, but always inferior quality of protein.   News Flash -- There is no plant source on the earth that is a complete protein!   Why?  Because plants do NOT contain nitrogen an important element of protein.

Completeness is not the only issue with respect to protein quality.   For the highest quality, proteins must not only be complete but also digestible, so that the sufficient numbers of amino acids are absorbed and reach the body's cells to permit them to make the proteins they need.   Although the proteins of rice and potatoes are a high quality plant source when combined together, a superior source of protein comes from eggs.   Egg protein tends to be retained in the body which indicates that it is utilized with little waste.   In fact, egg protein has been designated in the international scientific community to be the reference protein (100%) for the purpose of measuring protein quality, which is called a Protein Efficiency Ratio (PER).  Whey protein also has a very high PER.

To summarize:  In order for the human body to use proteins with maximum efficiency, the proteins must contain the essential amino acids, must be digestible, and must be consumed with sufficient energy from other sources such as complex carbohydrates, so the amino acids will not be used for energy (proteins are a reliable, sustainable source of energy -- much to some peoples disbelief).  If that is accomplished then the proteins will be available to build and repair lean body mass (blood, hair, skin, bones, connective tissues, organs, and muscle tissue).   If a sufficient amount of complex carbohydrates are denied the body it will automatically begin to use the amino acids for energy, thereby placing the body in a state of lean body mass "catabolism."  The proteins must also be accompanied by the vitamins and minerals needed to facilitate their use, and must be received by a healthy body able to use them.

Jenni Ross-Wilkinson, author of
"NUTRITION - THE MISSING LINK:   Personalizing Optimum Performance"


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