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March 5, 2009 5:13 PM

What are the essential amino acids necessary to human growth and development?

I'm fact-checking and have conflicting information from two sources, and I haven't been able to determine which is the most current and commonly-held belief. Are there eight or nine essential amino acids? I've read in one source that only 8 of the 20 amino acids are essential, while another says that 9 of the 20 are essential.

Is this just a situation where no one can agree? Someone, please tell me there is a right answer. And then give it to me.

posted by Felicity Rilke to Science & Nature (6 answers total)

It's 8 amino acids that are essential, meaning they can't be sympathized by the body. I've never heard of there being 9.
posted by royalsong at 5:19 PM on March 5, 2009

pvt tim hall?
posted by rux at 5:23 PM on March 5, 2009

According to wikipedia, there are essential amino acids, and then there are conditional essential amino acids, particularly for growth.

That may be the discrepancy that you were referring to.
posted by NucleophilicAttack at 5:29 PM on March 5, 2009

Best answer: More than you wanted to know on the topic (PDF).
posted by 517 at 9:43 PM on March 5, 2009

There are 22. And yes, you need them all but there were 8 now 9 (which science will soon discover) that are essential.
posted by watercarrier at 1:53 AM on March 6, 2009

Best answer: Amino acid requirements vary with age and relative health, so there is no definitive answer to the question. The 8 amino acids that can't be synthesized in the human body -- leucine, isoleucine, lysine, methionine, phenylalanine, threonine, tryptophan, and valine -- are unquestionably essential, but others such as arginine and histidine are sometimes included in the list because the amount made by the body may not be adequate during childhood, illness, etc.
posted by purplemonkie at 6:23 AM on March 6, 2009