Monday, April 03, 2006

Essential Amino Acids: 8 or 9?

For as long as I can recall, textbooks have indicated that there are eight essential amino acids required for proper nutrition in human adults and ten in growing children.  Recently, however, I have seen two texts that indicate the number of essential amino acids is nine.

Is this the current thinking and when did this change take place?  What research led to this decision?  What is the ninth essential amino acid?   Histidine?

I appreciate any information you can provide.



  • At 7:53 AM, Anonymous Michael G. Kurilla said…

    Histidine was not recognized originally as an essential amino acid. It was referred to as a conditional amino acid because it was thought to only be necessary during childhood growth.

    This oversight calls into question alot of the early nitrogen balance studies that are now considered inadequate. Histidine is complexed in tissues to alot of other minor components. In the absence of intake, the body can draw on these sources for quite some time and so any balance study that isn't long enough won't pick up the deficiency and the actual daily requirement.

    Mike Kurilla


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