A complete protein or whole protein is a food source of
protein
Proteins are large biomolecules and macromolecules that comprise one or more long chains of amino acid residue (biochemistry), residues. Proteins perform a vast array of functions within organisms, including Enzyme catalysis, catalysing metab ...
that contains an adequate proportion of each of the nine
essential amino acid
An essential amino acid, or indispensable amino acid, is an amino acid that cannot be synthesized from scratch by the organism fast enough to supply its demand, and must therefore come from the diet. Of the 21 amino acids common to all life forms ...
s necessary in the human
diet.
Concept
Protein nutrition is complex because any
proteinogenic amino acid
Proteinogenic amino acids are amino acids that are incorporated biosynthetically into proteins during translation from RNA. The word "proteinogenic" means "protein creating". Throughout known life, there are 22 genetically encoded (proteinogenic) ...
may be the
limiting factor
A limiting factor is a variable of a system that causes a noticeable change in output or another measure of a type of system. The limiting factor is in a pyramid shape of organisms going up from the producers to consumers and so on. A factor not l ...
in
metabolism
Metabolism (, from ''metabolē'', "change") is the set of life-sustaining chemical reactions in organisms. The three main functions of metabolism are: the conversion of the energy in food to energy available to run cellular processes; the co ...
. Mixing
livestock feed
Fodder (), also called provender (), is any agriculture, agricultural foodstuff used specifically to feed domesticated livestock, such as cattle, domestic rabbit, rabbits, sheep, horses, chickens and pigs. "Fodder" refers particularly to food ...
s can optimize for growth, or minimize cost while maintaining adequate growth. Similarly,
human nutrition
Human nutrition deals with the provision of essential nutrients in food that are necessary to support human life and good health. Poor nutrition is a chronic problem often linked to poverty, food security, or a poor understanding of nutrition ...
is subject to
Liebig's law of the minimum: The lowest level of one of the essential amino acids will be the limiting factor in metabolism.
:If the content of a single indispensable amino acid in the diet is less than the individual's requirement, then it will limit the utilization of other amino acids and thus prevent the normal rates of synthesis even when the total nitrogen intake level is adequate. Thus the "limiting amino acid" will determine the nutritional value of the total nitrogen or protein in the diet.
Protein sources are thus rated by their
limiting amino acids.
Most people eat a varied diet with multiple sources of protein. Incomplete sources can
complement each other and become complete when combined. Combining does not need to happen for every single meal: so long as the diet is varied and meets caloric needs, even vegans and vegetarians – people who tend to have more "incomplete protein" in their diet – can easily meet their amino acid needs. In other words, most people do not need to consider the completeness of proteins of single foods.
Amino acid profile
The following table lists the optimal profile of the nine essential amino acids in the human diet, which comprises complete protein, as recommended by the US
Institute of Medicine's Food and Nutrition Board. The foodstuffs listed for comparison show the essential amino acid content per unit of the total protein of the food; 100g of spinach, for example, only contains 2.9g of protein (6%
Daily Value
In the U.S. and Canada, the Reference Daily Intake (RDI) is used in nutrition labeling on food and dietary supplement products to indicate the daily intake level of a nutrient that is considered to be sufficient to meet the requirements of 97� ...
), and of that protein 1.36% is
tryptophan
Tryptophan (symbol Trp or W)
is an α-amino acid that is used in the biosynthesis of proteins. Tryptophan contains an α-amino group, an α-carboxylic acid group, and a side chain indole, making it a polar molecule with a non-polar aromat ...
.
Total adult daily intake
The second column in the following table shows the amino acid requirements of adults as recommended by the
World Health Organization
The World Health Organization (WHO) is a list of specialized agencies of the United Nations, specialized agency of the United Nations which coordinates responses to international public health issues and emergencies. It is headquartered in Gen ...
calculated for a adult. Recommended Daily Intake is based on per day,
which could be appropriate for a adult.
See also
*
Protein quality
Protein quality is the Digestion#Protein digestion, digestibility and quantity of essential amino acids for providing the proteins in correct ratios for human consumption. There are various methods that rank the quality of different types of prote ...
*
Protein Digestibility Corrected Amino Acid Score
Protein digestibility-corrected amino acid score (PDCAAS) is a method of evaluating the quality of a protein based on both the amino acid requirements of humans and their ability to digest it.
The PDCAAS rating was recommended by Food and Agric ...
References
{{Reflist
Nutrition
Proteins as nutrients