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.