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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, the nine amino acids humans cannot synthesize are valine, isoleucine, leucine, methionine, phenylalanine, tryptophan, threonine, histidine, and lysine.[1][2]

Six other amino acids are considered conditionally essential in the human diet, meaning their synthesis can be limited under special pathophysiological conditions, such as prematurity in the infant or individuals in severe catabolic distress.[2] These six are arginine, cysteine, glycine, glutamine, proline, and tyrosine. Six amino acids are non-essential (dispensable) in humans, meaning they can be synthesized in sufficient quantities in the body. These six are alanine, aspartic acid, asparagine, glutamic acid, serine,[2] and selenocysteine (considered the 21st amino acid). Pyrrolysine (considered the 22nd amino acid),[3] which is proteinogenic only in certain microorganisms, is not used by and therefore non-essential for most organisms, including humans.

The limiting amino acid is the essential amino acid which is furthest from meeting nutritional requirements.[4] This concept is important when determining the selection, number, and amount of foods to consume because even when total protein and all other essential amino acids are satisfied if the limiting amino acid is not satisfied then the meal is considered to be nutritionally limited by that amino acid.[3]

Essentiality in humans Edit

Of the twenty amino acids common to all life forms (not counting selenocysteine), humans cannot synthesize nine: histidine, isoleucine, leucine, lysine, methionine, phenylalanine, threonine, tryptophan and valine. Additionally, the amino acids arginine, cysteine, glutamine, glycine, proline and tyrosine are considered conditionally essential,[5] which means that specific populations who do not synthesize it in adequate amounts, such as new born infants and people with diseased livers who are unable to synthesize cysteine, must obtain one or more of these conditionally essential amino acids from their diet.[6][7] For example, enough arginine is synthesized by the urea cycle to meet the needs of an adult but perhaps not those of a growing child. Amino acids that must be obtained from the diet are called essential amino acids.

Essential Conditionally essential[8][9] Non-essential
Histidine (H) Arginine (R) Alanine (A)
Isoleucine (I) Cysteine (C) Aspartic acid (D)
Leucine (L) Glutamine (Q) Asparagine (N)
Lysine (K) Glycine (G) Glutamic acid (E)
Methionine (M) Proline (P) Serine (S)
Phenylalanine (F) Tyrosine (Y) Selenocysteine (U)
Threonine (T)
Pyrrolysine* (O)
Tryptophan (W)
Valine (V)

(*) Pyrrolysine, sometimes considered the "22nd amino acid", is not used by the human body.[10]

Eukaryotes can synthesize some of the amino acids from other substrates. Consequently, only a subset of the amino acids used in protein synthesis are essential nutrients.

From intermediates of the citric acid cycle and other pathways Edit

Nonessential amino acids are produced in the body. The pathways for the synthesis of nonessential amino acids come from basic metabolic pathways. Glutamate dehydrogenase catalyzes the reductive amination of α-ketoglutarate to glutamate. A transamination reaction takes place in the synthesis of most amino acids. At this step, the chirality of the amino acid is established. Alanine and aspartate are synthesized by the transamination of pyruvate and oxaloacetate, respectively. Glutamine is synthesized from NH4+ and glutamate, and asparagine is synthesized similarly. Proline and arginine are both derived from glutamate. Serine, formed from 3-phosphoglycerate, which comes from glycolysis, is the precursor of glycine and cysteine. Tyrosine is synthesized by the hydroxylation of phenylalanine, which is an essential amino acid.

Recommended daily intake Edit

Estimating the daily requirement for the indispensable amino acids has proven to be difficult; these numbers have undergone considerable revision over the last 20 years. The following table lists the recommended daily amounts currently in use for essential amino acids in adult humans (unless specified otherwise), together with their standard one-letter abbreviations.

Amino acid(s) Daily intake in mg per kg body mass
WHO[11] US NAM[12] FAO (2018) young children catch-up growth[13]
H Histidine 10 14 66
I Isoleucine 20 19 95
L Leucine 39 42 198
K Lysine 30 38 183
M Methionine
+ C Cysteine
10.4 + 4.1
(14.5 total)
19 total 88
F Phenylalanine
+ Y Tyrosine
25 (total) 33 total 177
T Threonine 15 20 103
W Tryptophan 4 5 29
V Valine 26 24 130

The recommended daily intakes for children aged three years and older is 10% to 20% higher than adult levels and those for infants can be as much as 150% higher in the first year of life. Cysteine (or sulfur-containing amino acids), tyrosine (or aromatic amino acids), and arginine are always required by infants and growing children.[11][14] Methionine and cysteine are grouped together because one of them can be synthesized from the other using the enzyme methionine S-methyltransferase and the catalyst methionine synthase.[15] Phenylalanine and tyrosine are grouped together because one of them can be synthesized from the other using the enzyme phenylalanine/tyrosine ammonia-lyase.[16]


Amino acid requirements and the amino acid content of food Edit

Historically, amino acid requirements were determined by calculating the balance between dietary Nitrogen intake and nitrogen excreted in the liquid and solid wastes because proteins represent the largest nitrogen content in a body. A positive balance is where more nitrogen is consumed than is excreted which indicates that some of the nitrogen is being used by the body to build proteins. A negative nitrogen balance is where more nitrogen is excreted than is consumed which indicates that there is insufficient intake for the body to maintain its health. Graduate students at the University of Illinois were fed an artificial diet so that there was a slightly positive nitrogen balance. Then one amino acid was omitted and the nitrogen balance recorded. If a positive balance continued then that amino acid was deemed not essential. If a negative balance occurred then that amino acid was slowly restored until a slightly positive nitrogen balance stabilized and the minimum amount recorded.[17][18]

A similar method was used to determine the protein content of foods. Test subjects were fed a diet containing no protein and the nitrogen losses recorded. During the first week or more there is a rapid loss of labile proteins. Once the nitrogen losses stabilized this baseline is determined to be the minimum required for maintenance. Then the test subjects were fed a measured amount of the food being tested. The difference between the nitrogen in that food and the nitrogen losses above baseline was the amount the body retained to rebuild proteins. The amount of nitrogen retained divided by the total nitrogen intake is called net protein utilization. The amount of nitrogen retained divided by the (nitrogen intake minus nitrogen loss above baseline) is called Biological Value and is usually given as a percentage.[18]

Modern techniques make use of Ion Exchange Chromatography to determine the actual amino acid content of foods. The USDA used this technique in their own labs to determine the content of 7793 foods across 28 categories and published the final database in 2018 to the public.[19]

The limiting amino acid depends on the human requirements and there are currently two sets of human requirements from authoritative sources: one published by WHO[11] and the other published by USDA.[12]

This table displays the number of Items in each Category with the same limiting Essential Amino Acid [11] [12] [19]
Based on WHO Requirements Based on USDA Requirements
Category
Tryptophan
Threonine
Isoleucine
Leucine
Lysine
Methionine+Cystine
Phenylalanine+Tyrosine
Valine
Histidine
Tryptophan
Threonine
Isoleucine
Leucine
Lysine
Methionine+Cystine
Phenylalanine+Tyrosine
Valine
Histidine
American Indian/Alaska Native Foods 4 0 0 10 4 0 0 15 0 7 2 0 3 6 5 0 0 10
Baby Foods 2 1 0 7 35 8 0 11 1 5 1 0 5 34 13 0 0 7
Baked Products 0 1 0 5 338 1 0 5 1 0 1 0 0 339 2 0 0 9
Beef Products 276 0 6 2 0 0 0 649 2 289 1 0 176 6 300 0 159 4
Beverages 0 0 0 2 11 5 0 1 1 0 0 0 1 12 5 0 0 2
Breakfast Cereals 0 0 1 1 40 1 0 0 0 0 0 1 1 40 1 0 0 0
Cereal Grains and Pasta 0 0 0 9 143 0 0 3 1 2 1 0 4 148 0 0 0 1
Dairy and Egg Products 19 6 4 21 16 122 0 12 3 19 19 0 0 11 122 0 0 32
Fast Foods 4 3 0 9 39 8 0 62 1 6 4 0 10 82 15 0 1 8
Fats and Oils 0 0 0 4 4 4 0 0 0 0 0 0 0 2 4 0 0 6
Finfish and Shellfish Products 3 3 0 15 0 0 0 228 0 5 3 0 174 0 0 0 0 67
Fruits and Fruit Juices 15 0 9 54 12 31 3 3 14 15 1 7 40 11 35 3 1 28
Lamb 10 0 5 254 3 2 0 155 0 10 0 2 207 9 112 0 2 87
Legumes and Legume Products 0 0 0 1 26 154 0 22 0 0 0 0 1 27 175 0 0 0
Meals 1 0 0 1 15 0 0 14 0 2 2 0 2 24 0 0 1 0
Nut and Seed Products 0 0 1 24 96 8 0 0 0 0 0 1 13 103 10 0 0 2
Pork Products 11 0 1 54 0 2 0 249 0 20 0 0 197 0 73 0 15 12
Poultry Products 6 12 6 58 1 0 0 287 0 36 22 0 167 5 8 0 99 33
Restaurant Foods 0 9 3 14 24 3 0 41 1 1 25 0 9 33 12 0 0 15
Sausages and Luncheon Meats 5 0 1 31 0 2 0 78 0 14 11 1 68 1 11 0 4 7
Snacks 2 0 0 6 83 6 0 4 1 2 1 0 6 81 9 0 0 3
Soups 0 0 2 7 10 28 0 7 0 0 0 0 1 21 31 0 0 1
Spices and Herbs 3 0 0 6 11 3 0 1 1 3 2 0 3 12 4 0 0 1
Sweets 0 1 0 3 17 47 0 1 2 0 1 0 1 17 47 0 0 5
Vegetables and Vegetable Products 7 0 8 238 114 199 0 18 19 13 28 0 112 144 246 0 2 58

Protein quality Edit

Various attempts have been made to express the "quality" or "value" of various kinds of protein. Measures include the biological value, net protein utilization, protein efficiency ratio, protein digestibility-corrected amino acid score and complete proteins concept. These concepts are important in the livestock industry, because the relative lack of one or more of the essential amino acids in animal feeds would have a limiting effect on growth and thus on feed conversion ratio. Thus, various feedstuffs may be fed in combination to increase net protein utilization, or a supplement of an individual amino acid (methionine, lysine, threonine, or tryptophan) can be added to the feed.

Protein per calorie Edit

Protein content in foods is often measured in protein per serving rather than protein per calorie. For instance, the USDA lists 6 grams of protein per large whole egg (a 50-gram serving) rather than 84 mg of protein per calorie (71 calories total).[20] For comparison, there are 2.8 grams of protein in a serving of raw broccoli (100 grams) or 82 mg of protein per calorie (34 calories total), or the Daily Value of 47.67g of protein after eating 1,690g of raw broccoli a day at 574 cal.[21] An egg contains 12.5g of protein per 100g, but 4 mg more protein per calorie, or the protein DV after 381g of egg, which is 545 cal.[22] The ratio of essential amino acids (the quality of protein) is not taken into account, one would actually need to eat more than 3 kg of broccoli a day to have a healthy protein profile, and almost 6 kg to get enough calories.[21] It is recommended that adult humans obtain between 10–35% of their 2000 calories a day as protein.[23]

Complete proteins in non-human animals Edit

Scientists had known since the early 20th century that rats could not survive on a diet whose only protein source was zein, which comes from maize (corn), but recovered if they were fed casein from cow's milk. This led William Cumming Rose to the discovery of the essential amino acid threonine.[24] Through manipulation of rodent diets, Rose was able to show that ten amino acids are essential for rats: lysine, tryptophan, histidine, phenylalanine, leucine, isoleucine, methionine, valine, and arginine, in addition to threonine. Rose's later work showed that eight amino acids are essential for adult human beings, with histidine also being essential for infants. Longer-term studies established histidine as also essential for adult humans.[25]

Interchangeability Edit

The distinction between essential and non-essential amino acids is somewhat unclear, as some amino acids can be produced from others. The sulfur-containing amino acids, methionine and homocysteine, can be converted into each other but neither can be synthesized de novo in humans. Likewise, cysteine can be made from homocysteine but cannot be synthesized on its own. So, for convenience, sulfur-containing amino acids are sometimes considered a single pool of nutritionally equivalent amino acids as are the aromatic amino acid pair, phenylalanine and tyrosine. Likewise arginine, ornithine, and citrulline, which are interconvertible by the urea cycle, are considered a single group.[citation needed]

Effects of deficiency Edit

If one of the essential amino acids is not available in the required quantities, protein synthesis will be inhibited, irrespective of the availability of the other amino acids.[2] Protein deficiency has been shown to affect all of the body's organs and many of its systems, for example affecting brain development in infants and young children; inhibiting upkeep of the immune system, increasing risk of infection; affecting gut mucosal function and permeability, thereby reducing absorption and increasing vulnerability to systemic disease; and impacting kidney function.[2] The physical signs of protein deficiency include edema, failure to thrive in infants and children, poor musculature, dull skin, and thin and fragile hair. Biochemical changes reflecting protein deficiency include low serum albumin and low serum transferrin.[2]

The amino acids that are essential in the human diet were established in a series of experiments led by William Cumming Rose. The experiments involved elemental diets to healthy male graduate students. These diets consisted of corn starch, sucrose, butterfat without protein, corn oil, inorganic salts, the known vitamins, a large brown "candy" made of liver extract flavored with peppermint oil (to supply any unknown vitamins), and mixtures of highly purified individual amino acids. The main outcome measure was nitrogen balance. Rose noted that the symptoms of nervousness, exhaustion, and dizziness were encountered to a greater or lesser extent whenever human subjects were deprived of an essential amino acid.[17]

Essential amino acid deficiency should be distinguished from protein-energy malnutrition, which can manifest as marasmus or kwashiorkor. Kwashiorkor was once attributed to pure protein deficiency in individuals who were consuming enough calories ("sugar baby syndrome"). However, this theory has been challenged by the finding that there is no difference in the diets of children developing marasmus as opposed to kwashiorkor.[26] Still, for instance in Dietary Reference Intakes (DRI) maintained by the USDA, lack of one or more of the essential amino acids is described as protein-energy malnutrition.[2]

See also Edit

References Edit

  1. ^ Young VR (1994). "Adult amino acid requirements: the case for a major revision in current recommendations". J. Nutr. 124 (8 Suppl): 1517S–1523S. doi:10.1093/jn/124.suppl_8.1517S. PMID 8064412.
  2. ^ a b c d e f g Otten, Jennifer J.; Hellwig, Jennifer Pitzi; Meyers, Linda D., eds. (2006) [1943]. Dietary Reference Intakes: The Essential Guide to Nutrient Requirements (Technical report). doi:10.17226/11537. ISBN 978-0-309-15742-1.
  3. ^ a b Lopez, Michael J.; Mohluddin, Shamim S. (18 March 2022). Biochemistry, Essential Amino Acids (Technical report).
  4. ^ "Limiting Amino Acids". National Agricultural Library. 30 November 2012. Retrieved 19 September 2022.
  5. ^ "PROTEIN AND AMINO ACID REQUIREMENTS IN HUMAN NUTRITION". 2007. p. 29.
  6. ^ Fürst P, Stehle P (1 June 2004). "What are the essential elements needed for the determination of amino acid requirements in humans?". J. Nutr. 134 (6 Suppl): 1558S–1565S. doi:10.1093/jn/134.6.1558S. PMID 15173430.
  7. ^ Reeds PJ (1 July 2000). "Dispensable and indispensable amino acids for humans". J. Nutr. 130 (7): 1835S–40S. doi:10.1093/jn/130.7.1835S. PMID 10867060.
  8. ^ Fürst P, Stehle P (1 June 2004). "What are the essential elements needed for the determination of amino acid requirements in humans?". Journal of Nutrition. 134 (6 Suppl): 1558S–1565S. doi:10.1093/jn/134.6.1558S. PMID 15173430.
  9. ^ Reeds PJ (1 July 2000). "Dispensable and indispensable amino acids for humans". J. Nutr. 130 (7): 1835S–40S. doi:10.1093/jn/130.7.1835S. PMID 10867060.
  10. ^ Richard Cammack. . Archived from the original on 12 September 2017. Retrieved 16 July 2012.
  11. ^ a b c d FAO/WHO/UNU (2007). Protein and amino acid requirements in human nutrition: report of a joint FAO/WHO/UNU expert consultation (PDF). WHO Press. ISBN 978-9241209359., page 150
  12. ^ a b c Institute of Medicine (2002). "Protein and Amino Acids". Dietary Reference Intakes for Energy, Carbohydrates, Fiber, Fat, Fatty Acids, Cholesterol, Protein, and Amino Acids. Washington, DC: The National Academies Press. p. 680. doi:10.17226/10490. ISBN 978-0-309-08525-0.
  13. ^ "Publication card | FAO | Food and Agriculture Organization of the United Nations". www.fao.org. p. x, Table 1 - Protein and amino acid requirement and amino acid reference pattern proposed for FUF-YC (1–2 year) and for RUTF (target weight gain value of 10 g/kg/d), in infants and children, 6 months to 5 years. Retrieved 6 March 2023.
  14. ^ Imura K, Okada A (1998). "Amino acid metabolism in pediatric patients". Nutrition. 14 (1): 143–8. doi:10.1016/S0899-9007(97)00230-X. PMID 9437700.
  15. ^ "Methionine and Cysteine metabolism". National Center for Biotechnology Information PubChem. 18 May 2022. Retrieved 21 September 2022.
  16. ^ "Phenylalanine and Tyrosine Metabolism". National Center for Biotechnology Information PubChem. 18 May 2022. Retrieved 21 September 2022.
  17. ^ a b Rose, WC; Haines, WJ; Warner, DT (1951). "The amino acid requirements of man. III. The role of isoleucine; additional evidence concerning histidine" (PDF). J Biol Chem. 193 (2): 605–612. doi:10.1016/S0021-9258(18)50916-9. PMID 14907749. Retrieved 15 December 2012.
  18. ^ a b McGilvery, Robert W. Ph.D.; et al. (Gerald Goldstein M.D.) (1979) [1970]. "Chapter 41 Nutrition: The Nitrogen Economy". Biochemistry, a Functional Approach (2nd ed.). W. B. Saunders Company. pp. 785–796. ISBN 0-7216-5912-8.
  19. ^ a b "FoodData Central Standard Reference (SR) Legacy Foods". U.S. Department of Agriculture, Agricultural Research Service. April 2019.
  20. ^ SDA National Nutrient Database for Standard Reference (Release 21 ed.). U.S. Department of Agriculture, Agricultural Research Service. 2008.
  21. ^ a b Vanovschi, Vitalii. "Broccoli, raw: nutritional value and analysis". www.nutritionvalue.org. Retrieved 4 November 2019.
  22. ^ Vanovschi, Vitalii. "Egg, poached, cooked, whole: nutritional value and analysis". www.nutritionvalue.org. Retrieved 4 November 2019.
  23. ^ "Web MD Protein: Are You Getting Enough?". webmd.com. 5 September 2014. Retrieved 31 March 2015.
  24. ^ Rose WC, Haines WJ, Warner DT, Johnson JE (1951). "The amino acid requirements of man. II. The role of threonine and histidine". The Journal of Biological Chemistry. 188 (1): 49–58. doi:10.1016/S0021-9258(18)56144-5. PMID 14814112.
  25. ^ Kopple JD, Swendseid ME (May 1975). "Evidence that histidine is an essential amino acid in normal and chronically uremic man". J Clin Invest. 55 (5): 881–891. doi:10.1172/JCI108016. PMC 301830. PMID 1123426.
  26. ^ Ahmed T, Rahman S, Cravioto A (2009). "Oedematous malnutrition". The Indian Journal of Medical Research. 130 (5): 651–4. PMID 20090122.

External links Edit

  • Amino acid content of some vegetarian foods at veganhealth.org.
  • at Virginia Tech.
  • Molecular Expressions: The Amino Acid Collection at Florida State University. Features detailed information and crystal photographs of each amino acid.
  • , an online software tool to analyze the essential amino acid profiles of single and pairs of plant based foods based on human requirements.

essential, amino, acid, also, protein, nutrient, protein, quality, essential, amino, acid, indispensable, amino, acid, amino, acid, that, cannot, synthesized, from, scratch, organism, fast, enough, supply, demand, must, therefore, come, from, diet, amino, acid. See also Protein nutrient and Protein quality 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 the nine amino acids humans cannot synthesize are valine isoleucine leucine methionine phenylalanine tryptophan threonine histidine and lysine 1 2 Six other amino acids are considered conditionally essential in the human diet meaning their synthesis can be limited under special pathophysiological conditions such as prematurity in the infant or individuals in severe catabolic distress 2 These six are arginine cysteine glycine glutamine proline and tyrosine Six amino acids are non essential dispensable in humans meaning they can be synthesized in sufficient quantities in the body These six are alanine aspartic acid asparagine glutamic acid serine 2 and selenocysteine considered the 21st amino acid Pyrrolysine considered the 22nd amino acid 3 which is proteinogenic only in certain microorganisms is not used by and therefore non essential for most organisms including humans The limiting amino acid is the essential amino acid which is furthest from meeting nutritional requirements 4 This concept is important when determining the selection number and amount of foods to consume because even when total protein and all other essential amino acids are satisfied if the limiting amino acid is not satisfied then the meal is considered to be nutritionally limited by that amino acid 3 Contents 1 Essentiality in humans 2 From intermediates of the citric acid cycle and other pathways 3 Recommended daily intake 4 Amino acid requirements and the amino acid content of food 4 1 Protein quality 4 2 Protein per calorie 5 Complete proteins in non human animals 6 Interchangeability 7 Effects of deficiency 8 See also 9 References 10 External linksEssentiality in humans EditOf the twenty amino acids common to all life forms not counting selenocysteine humans cannot synthesize nine histidine isoleucine leucine lysine methionine phenylalanine threonine tryptophan and valine Additionally the amino acids arginine cysteine glutamine glycine proline and tyrosine are considered conditionally essential 5 which means that specific populations who do not synthesize it in adequate amounts such as new born infants and people with diseased livers who are unable to synthesize cysteine must obtain one or more of these conditionally essential amino acids from their diet 6 7 For example enough arginine is synthesized by the urea cycle to meet the needs of an adult but perhaps not those of a growing child Amino acids that must be obtained from the diet are called essential amino acids Essential Conditionally essential 8 9 Non essentialHistidine H Arginine R Alanine A Isoleucine I Cysteine C Aspartic acid D Leucine L Glutamine Q Asparagine N Lysine K Glycine G Glutamic acid E Methionine M Proline P Serine S Phenylalanine F Tyrosine Y Selenocysteine U Threonine T Pyrrolysine O Tryptophan W Valine V Pyrrolysine sometimes considered the 22nd amino acid is not used by the human body 10 Eukaryotes can synthesize some of the amino acids from other substrates Consequently only a subset of the amino acids used in protein synthesis are essential nutrients From intermediates of the citric acid cycle and other pathways EditNonessential amino acids are produced in the body The pathways for the synthesis of nonessential amino acids come from basic metabolic pathways Glutamate dehydrogenase catalyzes the reductive amination of a ketoglutarate to glutamate A transamination reaction takes place in the synthesis of most amino acids At this step the chirality of the amino acid is established Alanine and aspartate are synthesized by the transamination of pyruvate and oxaloacetate respectively Glutamine is synthesized from NH4 and glutamate and asparagine is synthesized similarly Proline and arginine are both derived from glutamate Serine formed from 3 phosphoglycerate which comes from glycolysis is the precursor of glycine and cysteine Tyrosine is synthesized by the hydroxylation of phenylalanine which is an essential amino acid Recommended daily intake EditMain article Protein nutrient Estimating the daily requirement for the indispensable amino acids has proven to be difficult these numbers have undergone considerable revision over the last 20 years The following table lists the recommended daily amounts currently in use for essential amino acids in adult humans unless specified otherwise together with their standard one letter abbreviations Amino acid s Daily intake in mg per kg body massWHO 11 US NAM 12 FAO 2018 young children catch up growth 13 H Histidine 10 14 66I Isoleucine 20 19 95L Leucine 39 42 198K Lysine 30 38 183M Methionine C Cysteine 10 4 4 1 14 5 total 19 total 88F Phenylalanine Y Tyrosine 25 total 33 total 177T Threonine 15 20 103W Tryptophan 4 5 29V Valine 26 24 130The recommended daily intakes for children aged three years and older is 10 to 20 higher than adult levels and those for infants can be as much as 150 higher in the first year of life Cysteine or sulfur containing amino acids tyrosine or aromatic amino acids and arginine are always required by infants and growing children 11 14 Methionine and cysteine are grouped together because one of them can be synthesized from the other using the enzyme methionine S methyltransferase and the catalyst methionine synthase 15 Phenylalanine and tyrosine are grouped together because one of them can be synthesized from the other using the enzyme phenylalanine tyrosine ammonia lyase 16 Amino acid requirements and the amino acid content of food EditHistorically amino acid requirements were determined by calculating the balance between dietary Nitrogen intake and nitrogen excreted in the liquid and solid wastes because proteins represent the largest nitrogen content in a body A positive balance is where more nitrogen is consumed than is excreted which indicates that some of the nitrogen is being used by the body to build proteins A negative nitrogen balance is where more nitrogen is excreted than is consumed which indicates that there is insufficient intake for the body to maintain its health Graduate students at the University of Illinois were fed an artificial diet so that there was a slightly positive nitrogen balance Then one amino acid was omitted and the nitrogen balance recorded If a positive balance continued then that amino acid was deemed not essential If a negative balance occurred then that amino acid was slowly restored until a slightly positive nitrogen balance stabilized and the minimum amount recorded 17 18 A similar method was used to determine the protein content of foods Test subjects were fed a diet containing no protein and the nitrogen losses recorded During the first week or more there is a rapid loss of labile proteins Once the nitrogen losses stabilized this baseline is determined to be the minimum required for maintenance Then the test subjects were fed a measured amount of the food being tested The difference between the nitrogen in that food and the nitrogen losses above baseline was the amount the body retained to rebuild proteins The amount of nitrogen retained divided by the total nitrogen intake is called net protein utilization The amount of nitrogen retained divided by the nitrogen intake minus nitrogen loss above baseline is called Biological Value and is usually given as a percentage 18 Modern techniques make use of Ion Exchange Chromatography to determine the actual amino acid content of foods The USDA used this technique in their own labs to determine the content of 7793 foods across 28 categories and published the final database in 2018 to the public 19 The limiting amino acid depends on the human requirements and there are currently two sets of human requirements from authoritative sources one published by WHO 11 and the other published by USDA 12 This table displays the number of Items in each Category with the same limiting Essential Amino Acid 11 12 19 Based on WHO Requirements Based on USDA RequirementsCategory Tryptophan Threonine Isoleucine Leucine Lysine Methionine Cystine Phenylalanine Tyrosine Valine Histidine Tryptophan Threonine Isoleucine Leucine Lysine Methionine Cystine Phenylalanine Tyrosine Valine HistidineAmerican Indian Alaska Native Foods 4 0 0 10 4 0 0 15 0 7 2 0 3 6 5 0 0 10Baby Foods 2 1 0 7 35 8 0 11 1 5 1 0 5 34 13 0 0 7Baked Products 0 1 0 5 338 1 0 5 1 0 1 0 0 339 2 0 0 9Beef Products 276 0 6 2 0 0 0 649 2 289 1 0 176 6 300 0 159 4Beverages 0 0 0 2 11 5 0 1 1 0 0 0 1 12 5 0 0 2Breakfast Cereals 0 0 1 1 40 1 0 0 0 0 0 1 1 40 1 0 0 0Cereal Grains and Pasta 0 0 0 9 143 0 0 3 1 2 1 0 4 148 0 0 0 1Dairy and Egg Products 19 6 4 21 16 122 0 12 3 19 19 0 0 11 122 0 0 32Fast Foods 4 3 0 9 39 8 0 62 1 6 4 0 10 82 15 0 1 8Fats and Oils 0 0 0 4 4 4 0 0 0 0 0 0 0 2 4 0 0 6Finfish and Shellfish Products 3 3 0 15 0 0 0 228 0 5 3 0 174 0 0 0 0 67Fruits and Fruit Juices 15 0 9 54 12 31 3 3 14 15 1 7 40 11 35 3 1 28Lamb 10 0 5 254 3 2 0 155 0 10 0 2 207 9 112 0 2 87Legumes and Legume Products 0 0 0 1 26 154 0 22 0 0 0 0 1 27 175 0 0 0Meals 1 0 0 1 15 0 0 14 0 2 2 0 2 24 0 0 1 0Nut and Seed Products 0 0 1 24 96 8 0 0 0 0 0 1 13 103 10 0 0 2Pork Products 11 0 1 54 0 2 0 249 0 20 0 0 197 0 73 0 15 12Poultry Products 6 12 6 58 1 0 0 287 0 36 22 0 167 5 8 0 99 33Restaurant Foods 0 9 3 14 24 3 0 41 1 1 25 0 9 33 12 0 0 15Sausages and Luncheon Meats 5 0 1 31 0 2 0 78 0 14 11 1 68 1 11 0 4 7Snacks 2 0 0 6 83 6 0 4 1 2 1 0 6 81 9 0 0 3Soups 0 0 2 7 10 28 0 7 0 0 0 0 1 21 31 0 0 1Spices and Herbs 3 0 0 6 11 3 0 1 1 3 2 0 3 12 4 0 0 1Sweets 0 1 0 3 17 47 0 1 2 0 1 0 1 17 47 0 0 5Vegetables and Vegetable Products 7 0 8 238 114 199 0 18 19 13 28 0 112 144 246 0 2 58Protein quality Edit Main article Protein quality Various attempts have been made to express the quality or value of various kinds of protein Measures include the biological value net protein utilization protein efficiency ratio protein digestibility corrected amino acid score and complete proteins concept These concepts are important in the livestock industry because the relative lack of one or more of the essential amino acids in animal feeds would have a limiting effect on growth and thus on feed conversion ratio Thus various feedstuffs may be fed in combination to increase net protein utilization or a supplement of an individual amino acid methionine lysine threonine or tryptophan can be added to the feed Protein per calorie Edit Protein content in foods is often measured in protein per serving rather than protein per calorie For instance the USDA lists 6 grams of protein per large whole egg a 50 gram serving rather than 84 mg of protein per calorie 71 calories total 20 For comparison there are 2 8 grams of protein in a serving of raw broccoli 100 grams or 82 mg of protein per calorie 34 calories total or the Daily Value of 47 67g of protein after eating 1 690g of raw broccoli a day at 574 cal 21 An egg contains 12 5g of protein per 100g but 4 mg more protein per calorie or the protein DV after 381g of egg which is 545 cal 22 The ratio of essential amino acids the quality of protein is not taken into account one would actually need to eat more than 3 kg of broccoli a day to have a healthy protein profile and almost 6 kg to get enough calories 21 It is recommended that adult humans obtain between 10 35 of their 2000 calories a day as protein 23 Complete proteins in non human animals EditScientists had known since the early 20th century that rats could not survive on a diet whose only protein source was zein which comes from maize corn but recovered if they were fed casein from cow s milk This led William Cumming Rose to the discovery of the essential amino acid threonine 24 Through manipulation of rodent diets Rose was able to show that ten amino acids are essential for rats lysine tryptophan histidine phenylalanine leucine isoleucine methionine valine and arginine in addition to threonine Rose s later work showed that eight amino acids are essential for adult human beings with histidine also being essential for infants Longer term studies established histidine as also essential for adult humans 25 Interchangeability EditThe distinction between essential and non essential amino acids is somewhat unclear as some amino acids can be produced from others The sulfur containing amino acids methionine and homocysteine can be converted into each other but neither can be synthesized de novo in humans Likewise cysteine can be made from homocysteine but cannot be synthesized on its own So for convenience sulfur containing amino acids are sometimes considered a single pool of nutritionally equivalent amino acids as are the aromatic amino acid pair phenylalanine and tyrosine Likewise arginine ornithine and citrulline which are interconvertible by the urea cycle are considered a single group citation needed Effects of deficiency EditMain article Protein energy malnutrition If one of the essential amino acids is not available in the required quantities protein synthesis will be inhibited irrespective of the availability of the other amino acids 2 Protein deficiency has been shown to affect all of the body s organs and many of its systems for example affecting brain development in infants and young children inhibiting upkeep of the immune system increasing risk of infection affecting gut mucosal function and permeability thereby reducing absorption and increasing vulnerability to systemic disease and impacting kidney function 2 The physical signs of protein deficiency include edema failure to thrive in infants and children poor musculature dull skin and thin and fragile hair Biochemical changes reflecting protein deficiency include low serum albumin and low serum transferrin 2 The amino acids that are essential in the human diet were established in a series of experiments led by William Cumming Rose The experiments involved elemental diets to healthy male graduate students These diets consisted of corn starch sucrose butterfat without protein corn oil inorganic salts the known vitamins a large brown candy made of liver extract flavored with peppermint oil to supply any unknown vitamins and mixtures of highly purified individual amino acids The main outcome measure was nitrogen balance Rose noted that the symptoms of nervousness exhaustion and dizziness were encountered to a greater or lesser extent whenever human subjects were deprived of an essential amino acid 17 Essential amino acid deficiency should be distinguished from protein energy malnutrition which can manifest as marasmus or kwashiorkor Kwashiorkor was once attributed to pure protein deficiency in individuals who were consuming enough calories sugar baby syndrome However this theory has been challenged by the finding that there is no difference in the diets of children developing marasmus as opposed to kwashiorkor 26 Still for instance in Dietary Reference Intakes DRI maintained by the USDA lack of one or more of the essential amino acids is described as protein energy malnutrition 2 See also EditBiological Value BV Essential fatty acid Essential genes List of standard amino acids Low protein diet Orthomolecular medicine Protein Digestibility Corrected Amino Acid Score Ketogenic amino acid Glucogenic amino acidReferences Edit Young VR 1994 Adult amino acid requirements the case for a major revision in current recommendations J Nutr 124 8 Suppl 1517S 1523S doi 10 1093 jn 124 suppl 8 1517S PMID 8064412 a b c d e f g Otten Jennifer J Hellwig Jennifer Pitzi Meyers Linda D eds 2006 1943 Dietary Reference Intakes The Essential Guide to Nutrient Requirements Technical report doi 10 17226 11537 ISBN 978 0 309 15742 1 a b Lopez Michael J Mohluddin Shamim S 18 March 2022 Biochemistry Essential Amino Acids Technical report Limiting Amino Acids National Agricultural Library 30 November 2012 Retrieved 19 September 2022 PROTEIN AND AMINO ACID REQUIREMENTS IN HUMAN NUTRITION 2007 p 29 Furst P Stehle P 1 June 2004 What are the essential elements needed for the determination of amino acid requirements in humans J Nutr 134 6 Suppl 1558S 1565S doi 10 1093 jn 134 6 1558S PMID 15173430 Reeds PJ 1 July 2000 Dispensable and indispensable amino acids for humans J Nutr 130 7 1835S 40S doi 10 1093 jn 130 7 1835S PMID 10867060 Furst P Stehle P 1 June 2004 What are the essential elements needed for the determination of amino acid requirements in humans Journal of Nutrition 134 6 Suppl 1558S 1565S doi 10 1093 jn 134 6 1558S PMID 15173430 Reeds PJ 1 July 2000 Dispensable and indispensable amino acids for humans J Nutr 130 7 1835S 40S doi 10 1093 jn 130 7 1835S PMID 10867060 Richard Cammack Newsletter 2009 Biochemical Nomenclature Committee of IUPAC and NC IUBMB Archived from the original on 12 September 2017 Retrieved 16 July 2012 a b c d FAO WHO UNU 2007 Protein and amino acid requirements in human nutrition report of a joint FAO WHO UNU expert consultation PDF WHO Press ISBN 978 9241209359 page 150 a b c Institute of Medicine 2002 Protein and Amino Acids Dietary Reference Intakes for Energy Carbohydrates Fiber Fat Fatty Acids Cholesterol Protein and Amino Acids Washington DC The National Academies Press p 680 doi 10 17226 10490 ISBN 978 0 309 08525 0 Publication card FAO Food and Agriculture Organization of the United Nations www fao org p x Table 1 Protein and amino acid requirement and amino acid reference pattern proposed for FUF YC 1 2 year and for RUTF target weight gain value of 10 g kg d in infants and children 6 months to 5 years Retrieved 6 March 2023 Imura K Okada A 1998 Amino acid metabolism in pediatric patients Nutrition 14 1 143 8 doi 10 1016 S0899 9007 97 00230 X PMID 9437700 Methionine and Cysteine metabolism National Center for Biotechnology Information PubChem 18 May 2022 Retrieved 21 September 2022 Phenylalanine and Tyrosine Metabolism National Center for Biotechnology Information PubChem 18 May 2022 Retrieved 21 September 2022 a b Rose WC Haines WJ Warner DT 1951 The amino acid requirements of man III The role of isoleucine additional evidence concerning histidine PDF J Biol Chem 193 2 605 612 doi 10 1016 S0021 9258 18 50916 9 PMID 14907749 Retrieved 15 December 2012 a b McGilvery Robert W Ph D et al Gerald Goldstein M D 1979 1970 Chapter 41 Nutrition The Nitrogen Economy Biochemistry a Functional Approach 2nd ed W B Saunders Company pp 785 796 ISBN 0 7216 5912 8 a b FoodData Central Standard Reference SR Legacy Foods U S Department of Agriculture Agricultural Research Service April 2019 SDA National Nutrient Database for Standard Reference Release 21 ed U S Department of Agriculture Agricultural Research Service 2008 a b Vanovschi Vitalii Broccoli raw nutritional value and analysis www nutritionvalue org Retrieved 4 November 2019 Vanovschi Vitalii Egg poached cooked whole nutritional value and analysis www nutritionvalue org Retrieved 4 November 2019 Web MD Protein Are You Getting Enough webmd com 5 September 2014 Retrieved 31 March 2015 Rose WC Haines WJ Warner DT Johnson JE 1951 The amino acid requirements of man II The role of threonine and histidine The Journal of Biological Chemistry 188 1 49 58 doi 10 1016 S0021 9258 18 56144 5 PMID 14814112 Kopple JD Swendseid ME May 1975 Evidence that histidine is an essential amino acid in normal and chronically uremic man J Clin Invest 55 5 881 891 doi 10 1172 JCI108016 PMC 301830 PMID 1123426 Ahmed T Rahman S Cravioto A 2009 Oedematous malnutrition The Indian Journal of Medical Research 130 5 651 4 PMID 20090122 External links Edit nbsp Wikimedia Commons has media related to Essential amino acids Amino acid content of some vegetarian foods at veganhealth org Amino Acid Profiles of Some Common Feeds at Virginia Tech Molecular Expressions The Amino Acid Collection at Florida State University Features detailed information and crystal photographs of each amino acid vProtein an online software tool to analyze the essential amino acid profiles of single and pairs of plant based foods based on human requirements Retrieved from https en wikipedia org w index php title Essential amino acid amp oldid 1175067896, wikipedia, wiki, book, books, library,

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