An ESSENTIAL AMINO ACID, or INDISPENSABLE AMINO ACID, is an amino acid that cannot be synthesized de novo (from scratch) by the organism, and thus must be supplied in its diet. The nine amino acids humans cannot synthesize are phenylalanine , valine , threonine , tryptophan , methionine , leucine , isoleucine , lysine , and histidine (i.e., F V T W M L I K H).
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. These six are arginine , cysteine , glycine , glutamine , proline , and tyrosine (i.e., R C G Q P Y). Five amino acids are DISPENSABLE in humans, meaning they can be synthesized in the body. These five are alanine , aspartic acid , asparagine , glutamic acid and serine (i.e., A D N E S).
* 1 Essentiality in humans
* 2 Recommended daily intake
* 2.1 Relative amino acid composition of protein sources
* 3 Complete proteins in non-human animals * 4 Interchangeability * 5 Effects of deficiency * 6 See also * 7 References * 8 External links
ESSENTIALITY IN HUMANS
Asparagine * (N)
(*) Essential only in certain cases.
RECOMMENDED DAILY INTAKE
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
V Valine 26 1820 4
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.
RELATIVE AMINO ACID COMPOSITION OF PROTEIN SOURCES
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.
Although proteins from plant sources tend to have a relatively lower concentrations of protein by mass in comparison to protein from eggs or milk, they are nevertheless "complete" in that they contain at least trace amounts of all of the amino acids that are essential in human nutrition. Eating various plant foods in combination can provide a protein of higher biological value. Certain native combinations of foods, such as corn and beans, soybeans and rice, or red beans and rice, contain the essential amino acids necessary for humans in adequate amounts.
Additionally, certain types of algae and marine phytoplankton predate the division between animal and plant life on the planet; they have both chlorophyll as do plants, and also all the essential amino acids, as do animal proteins.
PROTEIN PER CALORIE
It can be shown that common vegetable sources contain adequate protein, often more protein per Calorie than the standard reference, whole raw egg, while other plant sources, particularly fruits contain less. For example, while 100 g of raw broccoli only provides 28 kcal and 3 g of protein, it has over 100 mg of protein per kcal. An egg contains five times as many calories (143 kcal) but only four times as much protein, roughly 90 mg of protein per kcal. However, a carrot has only 23 mg protein per kcal or twice the minimum recommendation, a banana meets the minimum, and an apple is below recommendation. It is recommended that adult humans obtain 10–35% of their calories as protein, or roughly 11–39 mg of protein per kcal per day (22–78 g for 2000 kcal). The US FDA daily reference value of 50 g protein per 2000 kcal is 25 mg/kcal per day.
SOURCE PROTEIN (G) CALORIES (KCAL) protein/Calorie (mg / kcal) L (MG) T (MG) W (MG) M+C (MG)
APPLES, RAW (100 G) 0.26 52 5 12 6 1 2
MINIMUM DAILY REFERENCE 22 2000 11
BANANAS, RAW (100 G) 1 89 11 500 28 9 17
CARROT, RAW (100 G) 1 41 24 101 191 12 103
US FDA DAILY /
UPPER DAILY REFERENCE 78 2000 39
PEANUT, VALENCIA, RAW (100 G) 48 570 84 1,627 859 244 630
SOYBEANS, MATURE SEEDS, DRY ROASTED (100 G) 43 449 96 3223 1719 575 1172
EGG, WHOLE, RAW (100 G) 13 143 91 912 556 167 652
BROCCOLI, RAW (100 G) 3 28 107 141 91 29 54
SOY SAUCE, TYPICAL (100 G) 11 60 183 729 403 182 576
BEEF, AUSTRALIAN, IMPORTED, GRASS-FED, GROUND, 85% LEAN / 15% FAT, RAW (100 G) 18 234 77 1430 780 200 690
COMPLETE PROTEINS IN NON-HUMAN ANIMALS
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 . 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.
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.
EFFECTS OF DEFICIENCY
Main article: Protein-energy malnutrition
If one of the essential amino acids is less than needed for an individual the utilization of other amino acids will be hindered and thus protein synthesis will be less than what it usually is, even in the presence of adequate total nitrogen intake.
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 cornstarch, 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.
Essential amino acid deficiency should be distinguished from
protein-energy malnutrition , which can manifest as marasmus or
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. Still, for instance in
Dietary Reference Intakes (DRI) maintained by the
* Biological Value (BV) * Complete protein * Edible protein per unit area of land * 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 acid
* ^ Young VR (1994). "Adult amino acid requirements: the case for a
major revision in current recommendations" (PDF). J. Nutr. 124 (8
Suppl): 1517S–1523S. PMID 8064412 .
* ^ A B C D E F G Dietary Reference Intakes: The Essential Guide to
Nutrient Requirements. Institute of Medicine's Food and Nutrition
* ^ 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. PMID
* ^ Reeds PJ (1 July 2000). "Dispensable and indispensable amino
acids for humans". J. Nutr. 130 (7): 1835S–40S. PMID 10867060 .
* ^ Richard Cammack. "Newsletter 2009, Biochemical Nomenclature
Committee of IUPAC and NC-IUBMB".
* ^ A B FAO/WHO/UNU (2007). "PROTEIN AND AMINO ACID REQUIREMENTS IN
HUMAN NUTRITION" (PDF).
* ^ 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. PMC 301830 . PMID 1123426 . doi :10.1172/JCI108016 . * ^ 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. PMID 14907749 . Retrieved 15 Dec 2012. * ^ Ahmed T, Rahman S, Cravioto A (2009). "Oedematous malnutrition". The Indian journal of medical research. 130 (5): 651–4. PMID 20090122 .