Some books say eight, others say nine. Both are reliable sources, so I don’t know what’s right.
Some websites even mention there being ten essential amino acids.
– Richard (Last name withheld)
New York, NY
Wonderful question. There does appear to be quite a bit of confusion on this issue.
There are eight truly essential amino acids:
Isoleucine
Leucine
Lysine
Methionine (chemistry fans: its structure is pictured alongside this post)
Phenylalanine
Threonine
Tryptophan
Valine
There are four “conditionally essential” amino acids:
Arginine
Cysteine
Histidine
Tyrosine
Some people erroneously consider one or two of them essential (which is where figures or “nine” or “ten” essential amino acids come from).
Arginine and histidine are conditionally essential because they are only essential for infants.
Tyrosine is produced from phenylalanine, an essential amino acid. People with phenylketoneuria (PKU) must strictly restrict their phenylalanine intake, thereby making tyrosine an essential amino acid.
Cysteine is produced from the essential amino acid methionine. Therefore, some people argue that cysteine is “conditionally essential”, since a diet lacking methionine is also void of cysteine.
Essential amino acid insufficiency is extremely rare in developed nations. Even in developing nations, it’s only really seen it with populations that do not eat animal products largely subsist on one crop.
Some books say eight, others say nine. Both are reliable sources, so I don’t know what’s right.
Some websites even mention there being ten essential amino acids.
– Richard (Last name withheld)
New York, NY
Wonderful question. There does appear to be quite a bit of confusion on this issue.
There are eight truly essential amino acids:
There are four “conditionally essential” amino acids:
Some people erroneously consider one or two of them essential (which is where figures or “nine” or “ten” essential amino acids come from).
Arginine and histidine are conditionally essential because they are only essential for infants.
Tyrosine is produced from phenylalanine, an essential amino acid. People with phenylketoneuria (PKU) must strictly restrict their phenylalanine intake, thereby making tyrosine an essential amino acid.
Cysteine is produced from the essential amino acid methionine. Therefore, some people argue that cysteine is “conditionally essential”, since a diet lacking methionine is also void of cysteine.
Essential amino acid insufficiency is extremely rare in developed nations. Even in developing nations, it’s only really seen it with populations that do not eat animal products largely subsist on one crop.