Editing Essential amino acid (section)

==Recommended daily intake==
{{Main|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.
{| class="wikitable"
! rowspan="2" | Essential (+ conditional) amino acid(s)
! colspan="3" | Daily intake in mg per kg body mass
|-
! WHO<ref name="WHO"/>
! US [[National Academy of Medicine|NAM]]<ref name="DRItext">{{cite book |last1=Institute of Medicine |title=Dietary Reference Intakes for Energy, Carbohydrates, Fiber, Fat, Fatty Acids, Cholesterol, Protein, and Amino Acids |chapter=Protein and Amino Acids |publisher=The National Academies Press |year=2002 |location=Washington, DC |page=680 |doi=10.17226/10490 |isbn=978-0-309-08525-0 |chapter-url=https://www.nap.edu/read/10490/chapter/12|author1-link=Institute of Medicine }}</ref>
!FAO (2018) young children catch-up growth<ref>{{Cite book |title=Publication card {{!}} FAO {{!}} Food and Agriculture Organization of the United Nations |url=https://www.fao.org/publications/card/en/c/CA2487EN |access-date=2023-03-06 |website=www.fao.org |page=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|isbn=978-92-5-131120-2 }}</ref>  
|-
| [[Histidine]] (H)
| 10
| 14
|66
|-
| [[Isoleucine]] (I)
| 20
| 19
|95
|-
| [[Leucine]] (L)
| 39
| 42
|198
|-
| [[Lysine]] (K)
| 30
| 38
|183
|-
| [[Methionine]] (M)<br />+ [[Cysteine]] (C)
| 10.4 + 4.1<br />(14.5 total)
| 19 total
|88
|-
| [[Phenylalanine]] (F)<br />+ [[Tyrosine]] (Y)
| 25 (total)
| 33 total
|177
|-
| [[Threonine]] (T)
| 15
| 20
|103
|-
| [[Tryptophan]] (W)
| 4
| 5
|29
|-
| [[Valine]] (V)
| 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.<ref name="WHO">{{cite book |url=https://apps.who.int/iris/bitstream/handle/10665/43411/WHO_TRS_935_eng.pdf |title=Protein and amino acid requirements in human nutrition: report of a joint FAO/WHO/UNU expert consultation|author=FAO/WHO/UNU |publisher=WHO Press |year=2007 |isbn=978-9241209359}}, page 150</ref><ref>{{cite journal |vauthors=Imura K, Okada A |title=Amino acid metabolism in pediatric patients |journal=Nutrition |volume=14 |issue=1 |pages=143–8 |year=1998 |pmid=9437700 |doi=10.1016/S0899-9007(97)00230-X}}</ref> [[Methionine]] and [[cysteine]] are grouped together because one of them can be synthesized from the other using the enzyme [[Methionine S-methyltransferase|methionine ''S''-methyltransferase]] and the catalyst [[methionine synthase]].<ref>{{cite web |title=Methionine and Cysteine metabolism |url=https://pubchem.ncbi.nlm.nih.gov/pathway/INOH:MI0036050 |publisher=National Center for Biotechnology Information PubChem |date=18 May 2022 |access-date=21 Sep 2022 }}</ref> [[Phenylalanine]] and [[tyrosine]] are grouped together because tyrosine can be synthesized from phenylalanine using the enzyme [[phenylalanine hydroxylase]].<ref>{{cite web |title=Phenylalanine and Tyrosine Metabolism |url=https://pubchem.ncbi.nlm.nih.gov/pathway/PathBank:SMP0000008 |publisher=National Center for Biotechnology Information PubChem |date=18 May 2022 |access-date=21 Sep 2022 }}</ref>