Essential amino acids refer to amino acids that cannot be synthesized by human body (or other vertebrates) or whose synthesis speed is far from meeting the needs of the body and must be supplied by food protein.For example, lysine, leucine, etc.[1]
Essential amino acids must be obtained directly from food, otherwise they cannot maintain the nitrogen balance of the body and affect health.[3]canMaintain normal metabolism, body stability and the health of the whole body.[20]The nutritional value of protein in food mainly depends on whether the type, content and proportion of essential amino acids are similar to those required by human body.Therefore,animal protein Quality andVegetable proteinThe nutritional value of plant protein can be improved by mixing different plant proteins.[2]
Chinese name
essential amino acid
Foreign name
essential amino acid EAA
Features
It cannot be synthesized or the synthesis speed cannot meet the needs of the body, and it must be supplied by food
Category
8 for adults, and histidine for infants
Discipline
Nutrition
Value
Maintain normal metabolism, body stability and the health of the whole body[20]
Amino acid is the basic unit of protein.[4]From the perspective of human nutrition, the 20 amino acids that constitute human protein can be divided into essential amino acids, conditional essential amino acids andNonessential amino acid。[3]
Essential amino acids refer to 9 kinds of essential amino acids that are needed by the human body but cannot be synthesized by itself or the synthesis speed cannot meet the needs of the body, namely lysine, tryptophan, phenylalaninemethionine, threonine, isoleucine, leucine, valine and histidine, of which histidine is essential for infants.In addition, arginine, cystine, tyrosine and taurine are essential amino acids for preterm infants.[3]
Transport and distribution
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Different amino acids have different transport mechanisms to maintain different concentration gradients.The gradient of essential amino acids inside and outside the cell is lower than that of nonessential amino acids.The transport of amino acids into and out of cells is completed by membrane binding proteins.The transport mechanism of amino acids through membrane carriers not only exists in intestinal mucosal cells, but also in renal tubular cells, muscle cellsfat cells, white blood cellsReticulocyteOn fibroblasts, it has universal significance for intracellular accumulation of amino acids.However, the nature of the vector may be different in different cells.[5]
It exists in human tissues, organs and body fluidsfree amino acid They are collectively called amino acid pools. In the intracellular and extracellular free amino acid pools, the concentration of different amino acids varies greatly.Basic amino acid(Arginine andglutamine）The concentration is very low in plasma, but highest in cells (skeletal muscle cells).[5]
In addition to food, most of the free amino acids in the amino acid pool come from protein decomposition products in the body.A small number of these amino acids are used to synthesize nitrogen containing compounds in the body, and they are mainly used to re synthesize human proteins to achieve continuous renewal and repair of body proteins.The unutilized nitrogen containing part is metabolized into urea, ammonia and creatinine, which are discharged from the body by urine, and the carbon containing part is converted into glycogen and fat.Therefore, the nitrogen excreted from urine includes food nitrogen and endogenous nitrogen.Normal people have about 55 mg/L of amino acid nitrogen outside the cell and 800 mg/L of amino acid nitrogen inside the cell, but the total amount of free amino acid nitrogen is less than that of protein bound amino acid nitrogen. The total amount of free amino acid nitrogen is 0.33 g/kg body weight, while the amount of body nitrogen is 24 g/kg body weight.[5]
Synthesis and degradation
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The protein in the body is always in the dynamic change of decomposition and synthesis.Different proteins have different renewal rates. If proteins are signal molecules, their renewal rates are relatively high.On the contrary, structural proteins (collagen and cardiac fibrin) have a relatively long life span.Presence in the bodySynthetic proteinThe special metabolic pathway of amino acid required also exists the metabolic pathway of amino acid degradation.[5]
20 amino acids that make up the human body
Various amino acids can be degraded according to specific chemical reactions.Most essential amino acids are mainly degraded in liver, while isoleucine, leucine and valine are mainly degraded in muscle, kidney and brain.On the one hand, the products after amino acid degradation can generate glucose through the gluconeogenesis process, such as the metabolic pathway of glucose alanine cycle, which is an effective amino acid gluconeogenesis pathway, and also provide energy for the body through the oxidation of amino acids, such as the oxidation of branched chain amino acids (leucine, isoleucine, valine),It can provide energy for long-term continuous movement.In addition, amino acid degradation products are also other nitrogen containing substances, such asglutathione, creatinine, creatinecarnitine, pyridine, etc.[5]
Species effect
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Proportion of amino acids in human body
There are 8 essential amino acids for adults:isoleucine、leucine、Lysine, methionine, phenylalanine, threonine, tryptophan, valine.Histidine synthesis in infants can not meet the needs, so infants (under 4 years old) need 9 essential amino acids.The remaining amino acids are nonessential amino acids, which can be obtained from food or synthesized from other nutrients in the body.Cysteine and tyrosine can be synthesized by methionine and phenylalanine respectively in the body. If these two amino acids are abundant in the diet, they can save methionine andPhenylalanineThe action of two essential amino acids, therefore, it is calledConditionally essential amino acid。[4]
Lys
essential amino acid
The structural formula of lysine is CsixHfourteenNtwoOtwo, one of the eight essential amino acids for adults, can regulate the metabolic balance of the human body and provide structural components for the synthesis of carnitine, which in turn can promote the synthesis of fatty acids in cells.Lysine can also improve the secretion of gastric juice, improve appetite and promote the growth and development of children.Lysine can improve calcium absorption and accelerate bone growth.Lysine deficiency may lead to anorexia, nutritional anemia, central nervous system damage, and dysplasiaprotein metabolism Obstacles, resulting inGrowth disorders。L-lysineIt has physiological activity,d-lysine No physiological activity.Lysine isHuman essential amino acidsOne, low content in cerealsFirst restricted amino acid。Lysine has an important physiological function in the human body. It is used to synthesize regenerative cells and nucleoprotein of brain nervehemoglobinIt is also an essential amino acid for important proteins, especially for infants and pregnant women.[6]
For infants in the development stage, because all organs are in the growth and development stage, they have high requirements for protein nutrition, especially for quality. If lysine is deficient, it will cause a serious lack of protein, affect the growth and development of infants, and even lead to mental development disorders and vulnerable to infection with various diseases.The best way to avoid lysine deficiency is to complement proteins and promote food diversification, especially with beans and animal foods.[6]
Phenylalanine (Phe)
Structural formula CnineHelevenNO2，Participate in eliminating the loss of kidney and bladder functions.[1]
Threonine
Structural formula CfourHnineNO3，It has the function of transforming some amino acids to achieve balance.[1]
Methionine
Structural formula CfiveHelevenNOtwoS. Also called methionine, it is involved in the formation of hemoglobin, tissue and serum, and has the function of promoting the metabolism of spleen, pancreas and lymph.[1]In human metabolism, choline and creatine can be synthesized. Choline is a substance against fatty liver.The methionine pair consists of arsenic agentBarbitalDrugscarbon tetrachlorideCaused by organic substancesToxic hepatitisIt has therapeutic and protective effects on liver function.[6]
Methionine is one of the essential amino acids for human body and the only one among themSulfur-containing amino acid。L-methionine is directly utilized by animal metabolic reactionActive methionine，D-methionineIt must be converted to L-methionine for biological utilization.L-methionine is a methyl donor of biochemical reactions in the human body, participating in variousmethylation, closely related to the metabolism of sulfur compounds, phosphorus metabolism andadrenaline、cholineandcreatineThe synthesis of is also related to it.The methyl group it carries can also detoxify toxic substances or drugs by methylation.[7]
essential amino acid
The US joint research team led by Jason W. Localale of Duke University School of Medicine has made new progress.Their latest research has proved that dietary methionine affects the treatment of cancer models in mice and changes human metabolism.Relevant papers were published in Nature on August 15, 2019.The research team proved that the reduction of the essential amino acid methionine (commonly known as methionine) of diet restriction has the characteristics of anti-aging and anti obesity through controlling and reproducible changes in single carbon metabolism, which will affect the prognosis of cancer.[8]
Tryptophan (Trp)
Tryptophan (CelevenHtwelveNtwoOtwo）It is an essential amino acid, which can be transformed into many physiologically important active substances in the body, such as5-hydroxytryptamineAnd the precursor of nicotinic acid, 5-hydroxytryptamine is an important neurotransmitter in the human body.In clinical practice, tryptophan can be used to treat bronchial asthma, especially for adolescents with identified antigens, and also for non infectious asthma.Tryptophan can also resist allergySeasonal rhinitis, acute and chronic allergic conjunctivitis and vernal keratoconjunctivitisAllergic eczemaAnd food induced intestinal anaphylaxis have good curative effect.[6]Tryptophan can promote the production of gastric juice and pancreatic juice.[1]
Val
Structural formula CfiveHelevenNOtwoIt acts on corpus luteum, breast and ovary.[1]
Leucine (Leu)
Structural formula CsixHthirteenNO2，It acts on the balance of isoleucine.[1]
Ile
Structural formula CsixHthirteenNO2，It is involved in the regulation and metabolism of thymus, spleen and sub brain gland.[1]
essential amino acid
Leucine, isoleucine and valine have the same branched side chains in structure, so they are calledBranched chain amino acid。Branched chain amino acids are the only amino acids metabolized outside the liver, mainly in skeletal muscle, accounting for about 35% of the essential amino acids of skeletal muscle protein, and are the main energy supply amino acids in the body.[6]
Its physiological functions are as follows:
① Save muscle consumption and reduce negative nitrogen balance: because branched chain amino acids are mainly catabolized in skeletal muscles, when the body is injured, seriously infected, burned and other diseases, the metabolism in the body is in a high catabolic state, especially when muscle proteins are largely decomposed to produce branched chain amino acids, which are consumed as the main source of maintaining body energy.The plasma level of branched chain amino acids decreased, and the human body gradually lost weight. This phenomenon is called "self cannibalism".Therefore, for diseases similar to the above hypercatabolism, we should pay attention to the supplement of branched chain amino acids while giving high energy.[6]
② Yeshepatic encephalopathyTreatment of liver cirrhosis or hepatic encephalopathy:Amino acid metabolismIt is characterized by a decrease in the content of plasma branched chain amino acids and an increase in the content of aromatic amino acids (phenylalanine, tyrosine).Aromatic amino acids can release an inhibitory neurotransmitter after entering the brain tissue. This neurotransmitter inhibits the cerebral cortex and leads to hepatic coma of hepatic encephalopathy.It is precisely that branched chain amino acids and aromatic amino acids are transported through the blood-brain barrier by one carrier, and they compete with each other to combine with the carrier. When the concentration of branched chain amino acids is high, they inhibitAromatic amino acidIt enters the brain tissue, so it is clinically used to treat liver coma with branched chain amino acids.It is often measured by the ratio of branched chain amino acids to aromatic amino acids. The ratio of normal people is 3.0-3.5, while that of patients with cirrhosis and hepatic coma is often reduced to below 1.5.After the patient is given BCAA, the liver coma will be relieved quickly, which is impossible for other anti coma drugs.[6]
Histidine (His)
Histidine (CsixHsevenNOtwo）It is an essential amino acid for infants during their growth and development.[9]
Key values
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Without these essential amino acids, the body cannot successfully synthesize the required proteins.[10]It can also be used as the basis for the division of protein nutritional value.[3]
Ingestion guidelines
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Food source
Animal foods, such as lean meat, milk, eggs, and fish, contain 8 essential amino acids in large quantities. The proportions of various amino acids are appropriate. Their biological characteristics are close to those of human beings, that is, they are similar to human protein structure and easy to be digested and absorbed by human beings.
In vegetable food, the protein in soybeans and oats isHigh quality proteinOthers, such as rice, noodles, fruits, beans and vegetablesVegetable proteinQuality is not a high-quality protein, and its amino acid composition is not comprehensive enough.Even the high quality protein in soybeans and oats still lags behind the protein in eggs, milk, fish and meat.[11]
In daily life, a series of cereal foods such as rice, white flour and corn lack lysine, which is an essential amino acid. However, beans (red beans, yellow beanskidney beanEtc.) contains a large amount of lysine.When we eat cereal and beans together, the amino acids in cereal shortboard are just supplemented by the superfluous amino acids in beans, forming a protein combination with high nutritional value.Therefore, for vegetarians or those who need to control their protein intake, cereal and beans can be eaten together in one meal, which can increase the value of protein.[12]
Represent food
essential amino acid
Laminaria japonica is a lower plant of brown algae between bacteria and higher plants.The algal body is a long, flat, brownish green thallus.Its chemical composition is mainly: sugar 57%, protein 8.2%, fat 0.1%, crude fiber 9.8%, inorganic elements calcium, iron, manganese, zinc, boron, iodine, selenium, potassium, vitamins, etc.The amino acids in kelp protein are complete and appropriate in proportion, especially the eight amino acids necessary for human body, whose content is very close to the content pattern of essential amino acids in ideal protein.[13]
The amino acid composition of protein in eggs is better, and its essential amino acid composition is basically similar to that of human body. Its biological value is also the best of all foods.[14]
Silkworm chrysalis is rich in protein and various amino acids, which is equivalent to pork loin, and does not have too much saturated fat.At the same time, the essential amino acids in the silkworm pupa protein are complete in variety, appropriate in proportion, easy to digest and absorb, and have a high utilization rate in the human body. It is a high-quality source of animal protein, which can be made intoAmino acid oral liquidas well asNutritional fortifierEtc.[15]
matters needing attention
Each kind of amino acid has important physiological functions. Only by comprehensively and evenly ingesting, can we maintain normal life activities of the human body.[16]
Non essential amino acids are also amino acids needed for human health, but relatively speaking, they do not have to be completely provided by food.Since essential amino acids can only come from food, the nutritional value of food protein depends to a large extent on the type and quantity of essential amino acids contained therein.[17]
Related concepts
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Conditionally essential amino acid
Sometimes under special conditions such as insufficient food sources or diseases, some nonessential amino acids will also be converted into essential amino acids, which are called conditionally essential amino acids (CEAA) orSemiessential amino acid(SEAA), such asCysteineMethionine and tyrosine are converted from methionine and phenylalanine respectively in human body. Therefore, methionine and cysteine, phenylalanine and tyrosine are often combined to calculate the content of essential amino acids.[10]
Nonessential amino acid
It is an amino acid that can be synthesized in animals and does not need to be supplemented externally as a nutrient source.Non essential amino acids are not unnecessary to the body, but can be synthesized by the body itself, or can be transformed from other amino acids to meet the needs of the body, and can not be supplied by food.There are usually 9 kinds of nonessential amino acids, including alanine, arginineAspartate、AsparagineGlutamic acid, glutamine, glycine, proline and serine.[3]
Essential amino acid pattern
Amino acid composition pattern of protein from different populations and high-quality animals[17]
Generally, the body needs and uses each essential amino acid within a certain range in the process of protein metabolism.To meetprotein synthesisThere should be an appropriate ratio between various essential amino acids.This proportion of the essential amino acids is calledEssential amino acid patternOr amino acid scoring mode.[3]
The calculation method of essential amino acid mode is to set the tryptophan content in the protein as 1, and then calculate the corresponding ratios of other essential amino acids respectively. This series of ratios is the amino acid mode of the protein.[3]
When food proteinAmino acid patternThe closer to human protein, the more essential amino acids can be fully absorbed and utilized in the body, and the higher their nutritional value is. Such proteins are called high-quality proteins. The main food sources of high-quality proteins are animal foods such as eggs, milk, meat, fish, and soybeans and their products.[3]
Restricted amino acid
If one or several essential amino acids in food protein are relatively low in content, other essential amino acids cannot be fully utilized in the body and are wasted, resulting in the reduction of protein nutritional value. These essential amino acids with relatively low content are calledRestricted amino acid, which can be called the first and second restricted amino acids according to the severity of their deficiency.[3]
Protein complementation
Meat protein
In order to improve the nutritional value of plant protein, two or more kinds of food are often mixed to eat, so as to supplement essential amino acids between different foods and improve the nutritional value of dietary protein.This kind of complementary action between different foods is called protein complementary action.Such as meat andsoybean protein It can make up for the lack of lysine in rice flour protein, and rice flour protein can make up for the lack of methionine in beans.[3]
Lysine and methionine are the main limiting amino acids in food.Generally, lysine is the first limiting amino acid of cereal protein, while methionine is the first limiting amino acid of most non cereal plant proteins.In addition, wheat, oats and rice are also deficient in threonine, and corn is deficient in tryptophan, which is their second limiting amino acid.Therefore, an appropriate amount of lysine is often added to some baked products, especially cereal based infant food to strengthen them.[3]
Complete protein
The essential amino acids contained are complete in variety, sufficient in quantity and appropriate in proportion to each other, which can not only maintain the health of adults, but also promote the growth and development of human body, such ascasein, in eggsovalbumin、Soy globulin, wheat glutenin, etc.[3]
Semi complete protein
It contains all kinds of essential amino acids, but the content of various amino acids is uneven and the proportion between them is not appropriate.As the only source of protein in the diet,Semi complete proteinIt can only maintain life, but cannot promote growth and development, such as glutenin in wheat and barley, in which lysine is the limiting amino acid.[3]
Incomplete protein
The essential amino acids contained are incomplete. When such proteins are used as the only source of protein in the diet, they can neither promote growth and development nor sustain life, such as corn gluten protein in corn and pea globulin.[3]
