Complete protein
Encyclopedia
A complete protein is a source of protein
that contains an adequate proportion of all nine of the essential amino acid
s necessary for the dietary needs of humans or other animals. Some incomplete protein sources may contain all essential amino acids, but a complete protein contains them in correct proportions for supporting biological functions in the human body.
The following table lists the optimal profile of the essential amino acids, which comprises a complete protein:
Nearly all whole foods
contain protein, and nearly all forms of protein contain all twenty protein-forming amino acids in some quantity. However, proportions vary, and some forms of protein are partly lacking in one or more of the essential amino acids. Meals prepared with a mix of protein foods can provide a better balance of the essential amino acids and therefore a more complete protein source. Apart from some exceptions such as quinoa
or soybeans, vegetable sources of protein are more often lower in one or more essential amino acids than animal sources, especially lysine
, and to a lesser extent methionine
and threonine
. Nonetheless, although cereal protein is particularly low in lysine compared to animal protein, even the lysine in cereals is adequate for adult needs. Because of growth, children and infants have a greater requirement for complete protein than adults.
A variety of proteins in the diet is one way of assuring that the body's amino acid needs are met. All the essential amino acids can be obtained on their own from various everyday plant sources, which, contrary to popular belief, do not need to be combined in the same meal (see Protein combining
).
Protein
Proteins are biochemical compounds consisting of one or more polypeptides typically folded into a globular or fibrous form, facilitating a biological function. A polypeptide is a single linear polymer chain of amino acids bonded together by peptide bonds between the carboxyl and amino groups of...
that contains an adequate proportion of all nine of the essential amino acid
Essential amino acid
An essential amino acid or indispensable amino acid is an amino acid that cannot be synthesized de novo by the organism , and therefore must be supplied in the diet.-Essentiality vs. conditional essentiality in humans:...
s necessary for the dietary needs of humans or other animals. Some incomplete protein sources may contain all essential amino acids, but a complete protein contains them in correct proportions for supporting biological functions in the human body.
The following table lists the optimal profile of the essential amino acids, which comprises a complete protein:
| Essential Amino Acid | mg/g of Protein |
|---|---|
| Tryptophan Tryptophan Tryptophan is one of the 20 standard amino acids, as well as an essential amino acid in the human diet. It is encoded in the standard genetic code as the codon UGG... |
7 |
| Threonine Threonine Threonine is an α-amino acid with the chemical formula HO2CCHCHCH3. Its codons are ACU, ACA, ACC, and ACG. This essential amino acid is classified as polar... |
27 |
| Isoleucine Isoleucine Isoleucine is an α-amino acid with the chemical formula HO2CCHCHCH2CH3. It is an essential amino acid, which means that humans cannot synthesize it, so it must be ingested. Its codons are AUU, AUC and AUA.... |
25 |
| Leucine Leucine Leucine is a branched-chain α-amino acid with the chemical formula HO2CCHCH2CH2. Leucine is classified as a hydrophobic amino acid due to its aliphatic isobutyl side chain. It is encoded by six codons and is a major component of the subunits in ferritin, astacin and other 'buffer' proteins... |
55 |
| Lysine Lysine Lysine is an α-amino acid with the chemical formula HO2CCH4NH2. It is an essential amino acid, which means that the human body cannot synthesize it. Its codons are AAA and AAG.... |
51 |
| Methionine Methionine Methionine is an α-amino acid with the chemical formula HO2CCHCH2CH2SCH3. This essential amino acid is classified as nonpolar. This amino-acid is coded by the codon AUG, also known as the initiation codon, since it indicates mRNA's coding region where translation into protein... +Cystine Cystine Cystine is a dimeric amino acid formed by the oxidation of two cysteine residues that covalently link to make a disulfide bond. This organosulfur compound has the formula 2. It is a white solid, and melts at 247-249 °C... |
25 |
| Phenylalanine Phenylalanine Phenylalanine is an α-amino acid with the formula C6H5CH2CHCOOH. This essential amino acid is classified as nonpolar because of the hydrophobic nature of the benzyl side chain. L-Phenylalanine is an electrically neutral amino acid, one of the twenty common amino acids used to biochemically form... +Tyrosine Tyrosine Tyrosine or 4-hydroxyphenylalanine, is one of the 22 amino acids that are used by cells to synthesize proteins. Its codons are UAC and UAU. It is a non-essential amino acid with a polar side group... |
47 |
| Valine Valine Valine is an α-amino acid with the chemical formula HO2CCHCH2. L-Valine is one of 20 proteinogenic amino acids. Its codons are GUU, GUC, GUA, and GUG. This essential amino acid is classified as nonpolar... |
32 |
| Histidine Histidine Histidine Histidine, an essential amino acid, has a positively charged imidazole functional group. It is one of the 22 proteinogenic amino acids. Its codons are CAU and CAC. Histidine was first isolated by German physician Albrecht Kossel in 1896. Histidine is an essential amino acid in humans... |
18 |
Nearly all whole foods
Whole foods
Whole foods are foods that are unprocessed and unrefined, or processed and refined as little as possible, before being consumed. Whole foods typically do not contain added ingredients, such as salt, carbohydrates, or fat. Examples of whole foods include unpolished grains, beans, fruits, vegetables...
contain protein, and nearly all forms of protein contain all twenty protein-forming amino acids in some quantity. However, proportions vary, and some forms of protein are partly lacking in one or more of the essential amino acids. Meals prepared with a mix of protein foods can provide a better balance of the essential amino acids and therefore a more complete protein source. Apart from some exceptions such as quinoa
Quinoa
Quinoa , a species of goosefoot , is a grain-like crop grown primarily for its edible seeds. It is a pseudocereal rather than a true cereal, or grain, as it is not a member of the grass family...
or soybeans, vegetable sources of protein are more often lower in one or more essential amino acids than animal sources, especially lysine
Lysine
Lysine is an α-amino acid with the chemical formula HO2CCH4NH2. It is an essential amino acid, which means that the human body cannot synthesize it. Its codons are AAA and AAG....
, and to a lesser extent methionine
Methionine
Methionine is an α-amino acid with the chemical formula HO2CCHCH2CH2SCH3. This essential amino acid is classified as nonpolar. This amino-acid is coded by the codon AUG, also known as the initiation codon, since it indicates mRNA's coding region where translation into protein...
and threonine
Threonine
Threonine is an α-amino acid with the chemical formula HO2CCHCHCH3. Its codons are ACU, ACA, ACC, and ACG. This essential amino acid is classified as polar...
. Nonetheless, although cereal protein is particularly low in lysine compared to animal protein, even the lysine in cereals is adequate for adult needs. Because of growth, children and infants have a greater requirement for complete protein than adults.
A variety of proteins in the diet is one way of assuring that the body's amino acid needs are met. All the essential amino acids can be obtained on their own from various everyday plant sources, which, contrary to popular belief, do not need to be combined in the same meal (see Protein combining
Protein combining
Protein combining is the outdated theory that vegetarians, particularly vegans, must eat certain complementary foods like beans and rice together in the same meal, so that plant foods with incomplete essential amino acid content combine to form a complete protein, meeting all amino acid...
).
Sources of complete protein
- Generally, proteins derived from animal foods (meats, fish, poultry, cheese, eggs, yogurt, and milk) are complete, though gelatinGelatinGelatin is a translucent, colorless, brittle , flavorless solid substance, derived from the collagen inside animals' skin and bones. It is commonly used as a gelling agent in food, pharmaceuticals, photography, and cosmetic manufacturing. Substances containing gelatin or functioning in a similar...
is an exception. Proteins derived from plant foods (legumes, grains, and vegetables) tend to be limited in essential amino acids. Some are notably low, such as corn protein, which is low in lysine and tryptophan. - Some foods contain all the essential amino acids on their own in a sufficient amount to qualify as a "complete protein". Complete protein foods that also obtain the highest possible PDCAASPDCAASProtein Digestibility Corrected Amino Acid Score is a method of evaluating the protein quality based on both the amino acid requirements of humans and their ability to digest it...
score of 1.0 are certain dairy products (including wheyWhey proteinWhey protein is a mixture of globular proteins isolated from whey, the liquid material created as a by-product of cheese production. Some preclinical studies in rodents have suggested that whey protein may possess anti-inflammatory or anti-cancer properties; however, human data is lacking...
), egg whiteEgg whiteEgg white is the common name for the clear liquid contained within an egg. In chickens it is formed from the layers of secretions of the anterior section of the hen's oviduct during the passage of the egg. It forms around either fertilized or unfertilized egg yolks...
s, and soy protein isolate. Other foods, such as amaranthAmaranthAmaranthus, collectively known as amaranth, is a cosmopolitan genus of herbs. Approximately 60 species are recognized, with inflorescences and foliage ranging from purple and red to gold...
, Aphanizomenon flos-aquaeAphanizomenon flos-aquaeAphanizomenon flos-aquae is a freshwater species of cyanobacteria. Cyanobacteria are an ancient clade of bacterial microphyte, part of the cyanobacteria phylum.AFA as a species has both toxic and nontoxic forms...
, buckwheatBuckwheatBuckwheat refers to a variety of plants in the dicot family Polygonaceae: the Eurasian genus Fagopyrum, the North American genus Eriogonum, and the Northern Hemisphere genus Fallopia. Either of the latter two may be referred to as "wild buckwheat"...
, hempHempHemp is mostly used as a name for low tetrahydrocannabinol strains of the plant Cannabis sativa, of fiber and/or oilseed varieties. In modern times, hemp has been used for industrial purposes including paper, textiles, biodegradable plastics, construction, health food and fuel with modest...
seed, meat, poultry, Salvia hispanicaSalvia hispanicaSalvia hispanica, commonly known as chia, is a species of flowering plant in the mint family, Lamiaceae, native to central and southern Mexico and Guatemala. The 16th century Codex Mendoza provides evidence that it was cultivated by the Aztec in pre-Columbian times; it has been said that it was an...
, soybeanSoybeanThe soybean or soya bean is a species of legume native to East Asia, widely grown for its edible bean which has numerous uses...
s, quinoaQuinoaQuinoa , a species of goosefoot , is a grain-like crop grown primarily for its edible seeds. It is a pseudocereal rather than a true cereal, or grain, as it is not a member of the grass family...
, seafoodSeafoodSeafood is any form of marine life regarded as food by humans. Seafoods include fish, molluscs , crustaceans , echinoderms . Edible sea plants, such as some seaweeds and microalgae, are also seafood, and are widely eaten around the world, especially in Asia...
, and spirulina also are complete protein foods, but may not obtain a PDCAAS score of 1.0.